RhIIICatalyzed Dehydrogenative Coupling of

FULL PAPER DOI: 10.1002/ejoc.201501246

RhIII-Catalyzed Dehydrogenative Coupling of Quinoline N-Oxides with Alkenes: N-Oxide as Traceless Directing Group for Remote C–H Activation Ritika Sharma,[a,b] Rakesh Kumar,[a,b] Inder Kumar,[a,b] and Upendra Sharma*[a,b] Keywords: C–H activation / Rhodium / Nitrogen heterocycles / Alkenes / Regioselectivity A RhIII-catalyzed dehydrogenative coupling reaction of quinoline N-oxides with alkenes has been developed that provides C-8 olefinated quinoline derivatives by employing a remote C–H activation strategy. Main features of this catalytic method include the use of N-oxide as a traceless directing group, the high selectivity of the reaction for the C-8 po-

sition, and the broad scope of possible substrates. Mechanistic studies have also been performed. A five-membered rhodacycle of quinoline N-oxide, a possible key reaction intermediate, was synthesized and characterized for the first time.

Introduction

of these reactions, an additional step was required to reduce the N-oxide group and afford the corresponding quinoline product. We envision a catalytic method in which the properties of the N-oxide can be combined to achieve the C-8– H activation/functionalization of the quinoline followed by the removal or use the N-oxide DG without an additional step.[14] The alkenylation of arenes (Fujiwara–Moritani reaction)[15] has become an ever fascinating goal for chemists because of the wide availability and cost effectiveness of alkenes.[16] Herein, we describe the first single-step RhIIIcatalyzed C-8 alkenylation of quinolines by using the dehydrogenative coupling of quinoline N-oxides with alkenes. The current approach is orthogonal to the Pd-catalyzed alkenylation of quinoline N-oxides, which provides 2-alkenylated quinolines.[17] Notably, earlier methods for the C-8 olefination of quinoline are limited in their substrate scope and involve the use of prefunctionalized substrates (Scheme 1).[18]

Transition-metal-catalyzed C–H activation reactions have emerged as a powerful approach in organic synthesis by providing efficient retrosynthetic pathways for the preparation of natural products and other important molecules.[1] Among these reactions, remote C–H activations are still in an early stage of development, and their advancement is ongoing.[2] The regioselectivity of these reactions is effectively tackled by employing different directing groups (DGs).[3] However, installation and removal of DGs can affect the step economy of C–H activation reactions. Ideally, this limitation can be overcome either by converting DGs into other desired functional groups or by removing them in succession with the desired C–H activation reaction.[4] Substituted quinolines are frequently encountered in natural products,[5] medicinal,[6] and materials chemistry.[7] Consequently, substantial efforts have been made towards their synthesis[8] and functionalization.[9] The C-2 position of quinoline is comparatively easy to functionalize because of its favorable electronic character and proximity.[10] In contrast, the functionalization of the C-8 position of quinoline is more challenging and remains unexplored.[11] Recently, installation of an N-oxide group into a quinoline moiety for use as a DG has emerged as an alternative approach for the functionalization of quinoline.[12] This strategy has been successfully applied to its C-8 functionalization by using Rh, Ir, and Pd catalysts.[13] However, in all [a] Natural Product Chemistry and Process Development Division, CSIR – Institute of Himalayan Bioresource Technology, Palampur, Himachal Pradesh 176061, India E-mail: [email protected] http://www.ihbt.res.in/php/cv/sctInfo.php?id=34049 [b] Academy of Scientific and Innovative Research, CSIR-IHBT, Palampur, Himachal Pradesh 176061, India Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejoc.201501246. Eur. J. Org. Chem. 2015, 7519–7528

Scheme 1. The C-8 olefination of quinoline (EWG = electron-withdrawing group).

Results and Discussion We commenced our study by treating commercially available quinoline N-oxide (1a) with ethyl acrylate (2a) in the presence of [Cp*RhCl2]2 (Cp* = 1,2,3,4,5-pentamethylcy-

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clopentadienyl), AgSbF6, Cu(OAc)2·H2O, and 1,2-dichloroethane (DCE) as the solvent for 24 h (Table 1, Entry 4) and were pleased to find that the quinoline underwent functionalization at the C-8 position along with the simultaneous removal of the oxygen atom. The product was unambiguously characterized by 1D NMR, 2D NMR, and HRMS analysis.[19] Table 1. Optimization study for olefination of N-oxide 1a with 2a.[a]

Entry

Variation from standard conditions

% Yield 3a[b]

1 2 3 4 5 6 7 8 9 10

none without catalyst no Cu(OAc)2·H2O without CH3CO2H at 80 °C instead of 100 °C DMF[d] instead of DCE TFT[d] as solvent Rh(acac)(nbd)[d] instead of [Cp*RhCl2]2 [Cp*IrCl2]2 instead of [Cp*RhCl2]2 [Ru(p-cymene)Cl2]2 instead of [Cp*RhCl2]2

84 (81)[c] n.d.[d] n.d. 40 51 29 33 trace trace n.d.

stituted quinoline N-oxide substrates afforded both the desired C-8 olefinated product and another unidentified product (Table 2, compound 3g). A fluoro-substituted quinoline N-oxide also yielded its corresponding product in 51 % yield (Table 2, compound 3n). No product was observed in the case of 6-nitro-substituted quinoline N-oxide (Table 2, compound 3o). The quinoline N-oxides that contained either a protected or unprotected alcohol group underwent the olefination at the C-8 position to afford the corresponding product in moderate yield and later oxidized to give the corresponding aldehyde (Table 2, compounds 3p and 3q). Carbonyl functional groups such as –COOMe were well tolerated under the reaction conditions and provided the expected products in good yields (Table 2, compounds 3r and 3s). An inseparable mixture of two products was observed Table 2. Scope of quinoline N-oxides and olefins.[a,19]

[a] Reagents and conditions: 1a (0.10 mmol), 2a (0.15 mmol), [Cp*RhCl2]2 (5 mol-%), AgSbF6 (20 mol-%), Cu(OAc)2·H2O (1 equiv.), acetic acid (1 equiv.), DCE (0.2 m), 100 °C, 24 h. [b] Yield determined by GC analysis of crude reaction mixture using n-heptane as the internal standard. [c] Isolated yield in parentheses. [d] n.d.: not detected, DMF = N,N-dimethylformamide, TFT = α,α,α-trifluorotoluene, acac = acetylacetonate, nbd = norbornadiene.

For control experiments, the reaction was first performed without the RhIII catalyst and then without Cu(OAc)2·H2O, but neither of these provided the desired product, which confirmed the necessity of both (Table 1, Entries 2 and 3). The efficiency of the reaction increased significantly when acetic acid was used as an additive. As a result, the desired product was afforded in 81 % isolated yield (Table 1, Entry 1). Other solvents such as DMF and TFT were less effective (Table 1, Entries 6 and 7). Various other organic and inorganic oxidants, solvents, and additives were also screened.[19] Other rhodium, iridium, and ruthenium catalysts were also explored, but they were unable to catalyze the current reaction (Table 1, Entry 8–10). With the optimal conditions in hand, we investigated the scope of various substituted quinoline N-oxides and acrylates (Table 2). Different acrylates underwent the reaction smoothly and gave the products in moderate to good yields (Table 2, compounds 3a–3f). Fortunately, the nature of the substituents at different positions of the quinoline N-oxide did not affect the outcome of the reaction. Quinoline Noxides with electron-donating groups, such as methyl and methoxy substituents, at different positions of its aromatic ring afforded the desired products in fair yields (Table 2, compounds 3h–3m), and the crystal structure of 3h was obtained by X-ray diffraction analysis.[19] Surprisingly, 2-sub7520

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[a] Reagents and conditions: 1 (0.10 mmol), 2 (0.15 mmol), [Cp*RhCl2]2 (5 mol-%), AgSbF6 (20 mol-%), Cu(OAc)2·H2O (1.0 equiv.), acetic acid (1.0 equiv.), DCE (0.2 m), 100 °C, 24 h. The reduction of quinoline N-oxide to give quinoline was observed as a side reaction. [b] Unidentified product was also observed. [c] (Quinolin-4-yl)methanol N-oxide was used as the reactant. [d] Another product, which corresponded to the unprotected aldehyde (7 %), was also detected by NMR analysis of the crude product.


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(Table 2, compound 3t) as a result of the reaction with the quinoline N-oxide that contained a protected aldehyde. In this case, the free aldehyde was observed along with the desired product. Polyaromatics such as acridine N-oxide and phenanthridine N-oxide smoothly underwent the reaction with ethyl acrylate to provide the desired products in synthetically useful yields (Table 2, compounds 3u and 3v). The crystal structure of 3v was obtained by X-ray diffraction analysis.[19] When styrene was treated with quinoline N-oxide under the optimized reaction conditions, a low yield of the corresponding olefinated product was observed (Table 3). Consequently, we further optimized the reaction conditions. It was interesting that the use of Cu(OAc)2 as the oxidant, DMF as the solvent, and 0.5 equiv. of acetic acid gave the desired product in 78 % isolated yield. The structure of 5a was confirmed by X-ray crystal structure analysis.[19]

The structure of products 5j and 5k were further confirmed by X-ray diffraction analysis.[19] Aliphatic olefins are often considered challenging substrates because of their unreactive nature.[16] Gratifyingly, our current method was also applicable to aliphatic olefins (Table 4). 1-Octene as well as allyl cyclohexane smoothly underwent the reaction with 2-methylquinoline N-oxide to provide the desired products, albeit in low yields (Table 4 compounds 7a and 7b). Table 4. Reaction of quinolines N-oxides with unactivated olefins.[a]

Table 3. Reaction of quinoline N-oxides with styrenes.[a,19]

[a] Reagents and conditions: 1 (0.1 mmol), 4 (0.15 mmol), [Cp*RhCl2]2 (5 mol-%), AgSbF6 (20 mol-%), Cu(OAc)2 (1 equiv.), acetic acid (0.5 equiv.), DMF (0.2 m), 100 °C, 24 h. The reduction of quinoline N-oxide to give quinoline was observed as side reaction.

For a mechanistic understanding, a series of deuteration reactions and other experiments were conducted. An intermolecular competition experiment between 1a and deuterated analogue 1a-d7 demonstrated a kinetic isotope effect of kH/kD ≈ 1.22 (Scheme 2, a). These results indicate that the cleavage of the C–H bond of quinoline N-oxide may not be involved in the rate-limiting step. Under the standard reaction conditions, a significant incorporation of deuterium was observed at both positions of the olefin in the presence of D2O (Scheme 2, b). The deuterium incorporation at the α- and β-positions of the final product might be a result [a] Reagents and conditions: 1 (0.10 mmol), 4 (0.15 mmol), [Cp*RhCl2]2 (5 mol-%), AgSbF6 (20 mol-%), Cu(OAc)2 (1 equiv.), acetic acid (0.5 equiv.), DMF (0.2 m), 100 °C, 24 h. The reduction of quinoline N-oxide to give quinoline was observed as a side reaction. [b] An unidentified product was also observed. [c] 4-Acetoxystyrene was used as the reactant.

In addition, various styrenes that contained different electron-withdrawing (COOMe, NO2, CN, or Ph) and electron-donating groups (Me or OMe) provided the products in moderate to good yields (Table 3). Halogen substituents on either of the reactants were also well tolerated and provided further opportunities for functionalization (Table 3, compounds 5c and 5f). 2-Vinylnaphthalene afforded its corresponding product in 41 % yield (Table 3, compound 5l). In contrast to the acrylates, only olefinated products were observed as a result of the reaction between styrene and a 2substituted quinoline N-oxide (Table 3, compounds 5d–5l). Eur. J. Org. Chem. 2015, 7519–7528

Scheme 2. Deuterium labeling experiments (KIE = kinetic isotope effect).[19]


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of the occurrence of a linear/branched process, in which the branched process is disfavored in the forward direction. In addition, the treatment of 1a under the standard reaction conditions in the absence of 2a but in the presence of D2O led to the recovery of the starting material with ⬎99 % incorporation of deuterium at the C-8 position (Scheme 2, c). These experiments suggest that rhodation at the C-8 position and carbometallation of the olefin are reversible in nature. Competition experiments with butyl acrylate reveal that electron-rich quinoline N-oxides are favored over electron-deficient quinoline N-oxides, which suggests that the electron-rich quinoline N-oxide is kinetically favored (Scheme 3).

Scheme 5. Role of Cu(OAc)2.

Scheme 3. Competition experiments.

The reaction of quinoline with ethyl acrylate under the standard reaction conditions did not provide the desired product, which confirmed the role of the N-oxide as a DG (Scheme 4, a).[19] Control experiments with stoichiometric amounts of [Cp*RhCl2]2 with or without a base in the absence of Cu(OAc)2·H2O showed that the rhodium complex alone was unable to promote the reaction (Scheme 4, b).[19]

Furthermore, we were able to synthesize five-membered rhodacycle A for the first time by treating 1a with [Cp*RhCl2]2 and NaOAc (Scheme 6, a).[13a,20] The structure of complex A was unambiguously confirmed by X-ray crystal structure analysis.[19] This is first report of the synthesis and full characterization of a five-membered rhodacycle with quinoline N-oxide, and we believe that this finding might be helpful with other related C-8 functionalizations of quinoline N-oxide. Although Li et al. have reported the formation of five-membered rhodacycle A, only mass spectrometry data were provided.[14a] Complex A was submitted to the olefination and successfully catalyzed the reaction of 1a with 2a to afford 3a in 45 % yield (Scheme 6, b). These experiments indicate that five-membered rhodacycle A could be an active species in the catalytic cycle of the olefination reaction.

Scheme 4. Control experiments.

Scheme 6. Synthesis of rhodacycle and its use as a catalyst in the olefination reaction.[19,23]

Next, to confirm the role of Cu(OAc)2, the standard reaction was carried out in the presence of acetate salts (i.e., KOAc and NH4OAc), which are unable to participate in a redox reaction (Scheme 5, a). No product was detected with the employment of KOAc, whereas only 10 % of the product was observed when NH4OAc was used. When (E)-ethyl 3(quinolin-8-yl)acrylate N-oxide was treated under the standard reaction conditions but in the absence of the Rh catalyst, the corresponding product was obtained in 42 % yield (Scheme 5, b).

Although a detailed mechanistic study is required, a plausible mechanism is depicted on the basis of preliminary mechanistic experiments and literature reports (Scheme 7).[21] The first step involves the formation of fivemembered rhodacycle A through the N-oxide-directed C–H bond cleavage. The coordination of the olefin by interacting with A followed by an insertion into Rh–C-8 bond afforded seven-membered rhodacycle C, which can undergo a β-hydride elimination to provide the corresponding N-oxide-coordinated intermediate D. Olefin insertion is a reversible

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process and can proceed through both orientations of the olefin to form the two isomeric seven-membered metallacycles C and D. However, the β-hydride elimination can only occur from metallacycle C, which eventually leads to the expected linear product. Intermediate E can undergo the reductive elimination of HCl to provide F and RhI. Under acidic conditions, Cu(OAc)2 probably acts as an oxidant to regenerate the Rh active species[21a] as well as a reductant[22] for the conversion of F into the final product (Scheme 7).

characterized by 1H NMR, 13C NMR, HRMS, and IR analysis. The 1H NMR spectroscopic data are reported in parts per million (ppm) relative to tetramethylsilane (δ = 0 ppm), and the residual protio solvent was used as the internal standard (for CHCl3 δ = 7.26 ppm, for CHD2COCD3 δ = 2.04 ppm). The 13C NMR spectroscopic data were reported in ppm relative to CDCl3 (δ = 77.23 ppm) and (CD3)2CO (δ = 29.35, 205.41 ppm). GC analysis was performed on a GC system that was equipped with a DB-5 fused silica capillary column (30 m, 0.25 μm i.d.), an AOC-20s auto sampler, an AOC-20i auto injector, and a flame ionization detector (FID). n-Heptane or n-decane was used as the internal standard. Preparation of Quinoline N-Oxides: Quinoline N-oxides were prepared according to previously reported procedures.[13a,13b] General Procedure for C-8 Olefination of Quinoline N-Oxides with Acrylates: To an oven-dried screw-cap reaction vial that was charged with a Spinvane magnetic stirring bar were added [Cp*RhCl2]2 (5 mol-%), AgSbF6 (20 mol-%), and Cu(OAc)2·H2O (0.10 mmol). The mode of addition for the quinoline N-oxide (0.10 mmol) and acrylate (0.15 mmol) was determined by their physical state. Solid compounds were weighed along with the other reagents, whereas liquid reagents and AcOH (0.10 mmol) were added by microliter syringe followed by the addition of DCE (0.2 m). The reaction vial was closed with the screw cap, and the reaction mixture was continuously stirred in a preheated oil bath or heating block at 100 °C for 24 h. Upon completion, the mixture was extracted with ethyl acetate. The organic layer was dried with anhydrous Na2SO4 and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel (230– 400 mesh; n-hexane/EtOAc).

Scheme 7. Proposed mechanism.

Conclusions In summary, we have developed a RhIII-catalyzed straightforward atom-economical method for access to C-8 olefinated quinolines. Quinoline N-oxides that contain various labile functional groups were successfully coupled with a number of acrylates, styrenes, and, remarkably, unactivated olefins to provide the corresponding C-8 olefinated quinolines in moderate to good yields. The N-oxide moiety acts as a traceless directing group, as it is removed under the reaction conditions to obviate an additional step. The transformation is operationally simple and requires readily available or easily synthesized starting materials.

Experimental Section General Methods: Unless otherwise stated, all reactions were carried out under air in screw-cap reaction vials. All solvents were purchased from commercial sources. They were contained in sureseal bottles and used as such. All chemicals were purchased from different commercial sources. Column chromatography was performed by using a gradient elution (n-hexane and ethyl acetate) based on Rf values, which were determined by TLC analysis [Merck aluminium sheets (silica gel 60 F254)]. All isolated compounds were Eur. J. Org. Chem. 2015, 7519–7528

Ethyl (E)-3-(Quinolin-8-yl)acrylate: (Table 2, compound 3a).[18b] Pale yellow solid (18.3 mg, 81 %); m.p. 55 °C. 1H NMR (600 MHz, C3D6O): δ = 9.00 (d, J = 1.8 Hz, 1 H), 8.98 (d, J = 16.2 Hz, 1 H), 8.37 (dd, J = 8.4, 1.8 Hz, 1 H), 8.21 (dd, J = 7.2, 0.6 Hz, 1 H), 8.03 (dd, J = 8.4, 1.2 Hz, 1 H), 7.65 (t, J = 7.8 Hz, 1 H), 7.57–7.59 (m, 1 H), 6.89 (d, J = 16.2 Hz, 1 H), 4.25 (q, J = 7.2 Hz, 2 H), 1.32 (t, J = 7.2 Hz, 3 H) ppm. 13C NMR (150 MHz, C3D6O): δ = 166.4, 150.4, 146.0, 140.4, 136.4, 132.5, 130.4, 128.6, 127.8, 126.4, 121.8, 119.9, 59.9, 13.8 ppm. IR (ZnSe): ν˜ = 2926, 2872, 1710, 1633, 1568, 1492, 1382, 1359, 1307, 1247, 1163, 1082, 991, 831, 796, 767, 721 cm–1. HRMS (EI): calcd. for C14H14NO2 [M + H]+ 228.1019; found 228.1002. Methyl (E)-3-(Quinoline-8-yl)acrylate: (Table 2, compound 3b). Brown resin (15.5 mg, 76 %). 1H NMR (600 MHz, C3D6O): δ = 8.98–9.01 (m, 2 H), 8.38 (d, J = 7.8 Hz, 1 H), 8.23 (d, J = 7.2 Hz, 1 H), 8.05 (d, J = 8.4 Hz, 1 H), 7.66 (t, J = 7.8 Hz, 1 H), 7.58–7.60 (m, 1 H), 6.91 (d, J = 16.2 Hz, 1 H), 3.79 (s, 3 H) ppm. 13C NMR (150 MHz, C3D6O): δ = 166.8, 150.4, 146.0, 140.6, 136.4, 132.4, 130.4, 128.6, 127.8, 126.4, 121.8, 119.4, 50.9 ppm. IR (ZnSe): ν˜ = 2951, 1703, 1631, 1570, 1494, 1433, 1386, 1311, 1251, 1163, 1045, 987, 866, 827, 792, 758 cm–1. HRMS (EI): calcd. for C13H12NO2 [M + H]+ 214.0863; found 214.0841. Butyl (E)-3-(Quinoline-8-yl)acrylate: (Table 2, compound 3c). Brown resin (13 mg, 51 %). 1H NMR (600 MHz, C3D6O): δ = 8.99 (d, J = 16.2 Hz, 2 H), 8.38 (d, J = 8.4 Hz, 1 H), 8.24 (d, J = 7.2 Hz, 1 H), 8.05 (d, J = 7.8 Hz, 1 H), 7.66 (t, J = 7.8 Hz, 1 H), 7.59 (dd, J = 8.4, 4.2 Hz, 1 H), 6.91 (d, J = 16.2 Hz, 1 H), 4.22 (m, 2 H), 1.67–1.72 (m, 2 H), 1.42–1.48 (m, 2 H), 0.96 (t, J = 7.2 Hz, 3 H) ppm. 13C NMR (150 MHz, C3D6O): δ = 166.4, 150.4, 146.0, 140.4, 136.4, 132.5, 130.4, 128.6, 127.8, 126.4, 121.8, 119.9, 63.7, 30.7, 18.9, 13.1 ppm. IR (ZnSe): ν˜ = 2956, 2872, 1705, 1631, 1571, 1494, 1467, 1390, 1307, 1284, 1251, 1163, 989, 827, 792 cm–1.


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HRMS (EI): calcd. for C16H18NO2 [M + H]+ 256.1332; found 256.1309. tert-Butyl (E)-3-(Quinolin-8-yl)acrylate: (Table 2, compound 3d). Light yellow resin (11.7 mg, 46 %). 1H NMR (600 MHz, CDCl3): δ = 9.0 (d, J = 3.0 Hz, 1 H), 8.82 (d, J = 18.0 Hz, 1 H), 8.17 (d, J = 6.0 Hz, 1 H), 7.97 (d, J = 9.0 Hz, 1 H), 7.85 (d, J = 6.0 Hz, 1 H), 7.53–7.58 (m, 1 H), 7.44–7.48 (m, 1 H), 6.76 (d, J = 18.0 Hz, 1 H), 1.59 (s, 9 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 166.6, 150.1, 146.2, 140.2, 136.1, 133.4, 129.6, 128.1, 127.6, 125.9, 122.5, 121.2, 80.1, 28.2 ppm. IR (ZnSe): ν˜ = 2976, 2933, 1697, 1631, 1571, 1494, 1388, 1365, 1313, 1288, 1145, 979, 889, 827, 790, 758 cm–1. HRMS (EI): calcd. for C16H18NO2 [M + H]+ 256.1332; found 256.1312. Benzyl (E)-3-(Quinolin-8-yl)acrylate: (Table 2, compound 3e). Orange resin (15.8 mg, 55 %). 1H NMR (600 MHz, CDCl3): δ = 8.98 (d, J = 3.6 Hz, 1 H), 8.95 (d, J = 16.2 Hz, 1 H), 8.17 (d, J = 8.4 Hz, 1 H), 7.98 (d, J = 7.2 Hz, 1 H), 7.86 (d, J = 8.4 Hz, 1 H), 7.56 (t, J = 7.8 Hz, 1 H), 7.46 (t, J = 6.6 Hz, 3 H), 7.38–7.40 (m, 2 H), 7.33–7.35 (m, 1 H), 6.91 (d, J = 16.2 Hz, 1 H), 5.31 (s, 2 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 166.9, 150.2, 146.2, 141.6, 136.2, 133.1, 130.1, 128.5, 128.4, 128.3, 128.2, 128.1, 126.2, 121.5, 120.4, 66.3 ppm. IR (ZnSe): ν˜ = 3034, 2929, 2854, 1708, 1629, 1571, 1494, 1303, 1249, 1153, 987, 827, 792, 750, 734, 694 cm–1. HRMS (EI): calcd. for C19H16NO2 [M + H]+ 290.1176; found 290.1159. Diethyl (E)-2-(Quinolyn-8-yl)vinylphosphonate: (Table 2, compound 3f). Light yellow resin (13.1 mg, 45 %). 1H NMR (600 MHz, CDCl3): δ = 8.96–8.97 (m, 1 H), 8.67 (m, 1 H), 8.15–8.17 (m, 1 H), 7.96 (d, J = 7.2 Hz, 1 H), 7.85 (d, J = 8.4 Hz, 1 H), 7.57 (t, J = 7.8 Hz, 1 H), 7.44–7.46 (m, 1 H), 6.77 (dd, J = 18, 19.8 Hz, 1 H), 4.17–4.22 (m, 4 H), 1.38–1.41 (m, 6 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 150.2, 146.1, 144.9, 136.1, 129.9, 128.4, 127.8, 126.1, 121.5, 117.2, 115.9, 61.9, 61.9, 29.7, 16.4, 16.4 ppm. IR (ZnSe): ν˜ = 2922, 2850, 1726, 1670, 1593, 1467, 1386, 1232, 1195, 1047, 1020, 958, 858, 817, 796, 761 cm–1. HRMS (EI): calcd. for C15H19NO3P [M + H]+ 292.1097; found 292.1065. Ethyl (E)-3-(2-Methylquinolin-8-yl)acrylate: (Table 2, compound 3g). Brown resin (7.2 mg, 30 %). 1H NMR (600 MHz, CDCl3): δ = 8.96 (d, J = 15.0 Hz, 1 H), 8.04 (d, J = 12.0 Hz, 1 H), 7.97 (d, J = 6.0 Hz, 1 H), 7.81 (d, J = 9.0 Hz, 1 H), 7.51 (d, J = 6.0 Hz, 1 H), 7.33 (d, J = 9.0 Hz, 1 H), 6.85 (d, J = 18.0 Hz, 1 H), 4.30–4.37 (m, 2 H), 2.80 (s, 3 H), 1.37–1.42 (m, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 167.1, 159.2, 145.6, 141.3, 136.1, 132.3, 129.5, 127.9, 126.6, 125.1, 122.0, 120.1, 60.1, 25.0, 14.0 ppm. IR (ZnSe): ν˜ = 2956, 2899, 1709, 1631, 1543, 1397, 1367, 1180, 1087, 946, 806, 654 cm–1. HRMS (EI): calcd. for C15H16NO2 [M + H]+ 242.1176; found 242.1195. Ethyl (E)-3-(3-Methylquinoline-8-yl)acrylate: (Table 2, compound 3h). Pale yellow needles (15.4 mg, 64 %); m.p. 70 °C. 1H NMR (600 MHz, CDCl3): δ = 8.88 (d, J = 16.2 Hz, 1 H), 8.83 (s, 1 H), 7.91 (d, J = 7.2 Hz, 2 H), 7.77 (d, J = 7.8 Hz, 1 H), 7.50– 7.53 (m, 1 H), 6.82 (d, J = 16.2 Hz, 1 H), 4.39–4.33 (m, 2 H), 2.53 (s, 3 H), 1.37 (t, J = 7.2 Hz, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 167.1, 152.2, 144.5, 141.1, 134.8, 132.9, 131.0, 129.3, 128.3, 127.1, 126.2, 120.6, 60.4, 18.6, 14.4 ppm. IR (ZnSe): ν˜ = 2920, 2839, 1703, 1631, 1477, 1309, 1265, 1228, 1180, 1087, 995, 956, 866, 767 cm–1. HRMS (EI): calcd. for C15H16NO2 [M + H]+ 242.1176; found 242.1150. Butyl (E)-3-(4-Methylquinolin-8-yl)acrylate: (Table 2, compound 3i). Yellow resin (9.9 mg, 37 %). 1H NMR (600 MHz, CDCl3): δ = 8.93 (d, J = 16.2 Hz, 1 H), 8.83 (d, J = 4.2 Hz, 1 H), 8.04 (d, J = 7.8 Hz, 1 H), 7.97 (d, J = 7.8 Hz, 1 H), 7.56 (t, J = 7524

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7.8 Hz, 1 H), 7.27 (d, J = 4.2 Hz, 1 H), 6.76 (d, J = 16.2 Hz, 1 H), 4.25 (t, J = 6.6 Hz, 2 H), 2.71 (s, 3 H), 1.70–1.75 (m, 2 H), 1.43–1.49 (m, 2 H), 0.96–0.98 (m, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 167.2, 149.8, 146.0, 144.3, 141.4, 133.7, 128.4, 127.5, 125.9, 125.9, 122.3, 120.5, 64.3, 30.8, 19.2, 18.9, 13.7 ppm. IR (ZnSe): ν˜ = 2958, 2929, 2872, 1705, 1631, 1595, 1390, 1305, 1249, 1165, 1145, 837, 759 cm–1. HRMS (EI): calcd. for C17H20NO2 [M + H]+ 270.1489; found 270.1465. Methyl (E)-3-(6-Methylquinoline-8-yl)acrylate: (Table 2, compound 3j). Light orange solid (18.8 mg, 83 %); m.p. 59 °C. 1H NMR (600 MHz, CDCl3): δ = 8.89 (dd, J = 4.2, 1.8 Hz, 1 H), 8.86 (d, J = 16.2 Hz, 1 H), 8.04 (dd, J = 8.4, 1.8 Hz, 1 H), 7.79 (d, J = 1.2 Hz, 1 H), 7.59 (s, 1 H), 7.39 (q, J = 4.2 Hz, 1 H), 6.80 (d, J = 16.2 Hz, 1 H), 3.84 (s, 3 H), 2.53 (s, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 167.5, 149.4, 144.8, 141.2, 136.0, 135.5, 132.6, 130.1, 129.0, 128.5, 121.5, 120.0, 51.6, 21.5 ppm. IR (ZnSe): ν˜ max = 2924, 2850, 1693, 1570, 1435, 1271, 1037, 999, 875, 860, 783 cm–1. HRMS (EI): calcd. for C14H14NO2 [M + H]+ 228.1019; found 228.1009. Ethyl (E)-3-(6-Methylquinoline-8-yl)acrylate: (Table 2, compound 3k). Yellow resin (14.4 mg, 60 %). 1H NMR (600 MHz, CDCl3): δ = 8.91 (s, 1 H), 8.85 (d, J = 16.2 Hz, 1 H), 8.05 (d, J = 8.4 Hz, 1 H), 7.81 (s, 1 H), 7.61 (s, 1 H), 7.39–7.40 (t, J = 4.2 Hz, 1 H), 6.82 (d, J = 16.2 Hz, 1 H), 4.29–4.32 (m, 2 H), 2.54 (s, 3 H), 1.37 (t, J = 6.6 Hz, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 167.1, 149.3, 144.8, 140.9, 135.9, 135.5, 132.7, 130.2, 128.9, 128.5, 121.5, 120.5, 60.4, 21.5, 14.4 ppm. IR (ZnSe): ν˜ = 2978, 2920, 2852, 1703, 1631, 1570, 1489, 1365, 1305, 1247, 1174, 1159, 1035, 1128, 858, 785 cm–1. HRMS (EI): calcd. for C15H16NO2 [M + H]+ 242.1176; found 242.1150. Butyl (E)-3-(6-Methylquinoline-8-yl)acrylate: (Table 2, compound 3l). Dark orange resin (20.7 mg, 77 %). 1H NMR (600 MHz, C3D6O): δ = 8.93 (d, J = 16.2 Hz, 1 H), 8.90 (dd, J = 2.4, 1.8 Hz, 1 H), 8.24 (dd, J = 7.8, 1.8 Hz, 1 H), 8.07 (d, J = 1.2 Hz, 1 H), 7.77 (s, 1 H), 7.51–7.53 (m, 1 H), 6.90 (d, J = 16.2 Hz, 1 H), 4.21 (t, J = 6.6 Hz, 2 H), 2.55 (s, 3 H), 1.67–1.72 (m, 2 H), 1.43–1.47 (m, 2 H), 0.95–0.97 (m, 3 H) ppm. 13C NMR (150 MHz, C3D6O): δ = 166.5, 149.4, 144.7, 140.4, 136.2, 135.7, 132.1, 129.9, 129.2, 128.6, 121.7, 119.8, 63.7, 30.7, 20.5, 18.9, 13.1 ppm. IR (ZnSe): ν˜ = 2956, 2926, 2870, 1705, 1631, 1570, 1386, 1305, 1247, 1172, 1159, 1066, 983, 858 cm–1. HRMS (EI): calcd. for C17H20NO2 [M + H]+ 270.1489; found 270.1471. Butyl (E)-3-(6-Methoxyquinoline-8-yl)acrylate: (Table 2, compound 3m). Yellow resin (16.3 mg, 57 %). 1H NMR (600 MHz, CDCl3): δ = 8.81–8.84 (m, 1 H), 8.04 (d, J = 12 Hz, 1 H), 7.61 (s, 1 H), 7.38–7.40 (m, 1 H), 7.11 (s, 1 H), 6.79 (d, J = 18.0 Hz, 1 H), 4.26 (t, J = 6.0 Hz, 1 H), 3.94 (s, 3 H), 1.71–1.76 (m, 2 H), 1.44–1.50 (m, 2 H), 0.97–1.0 (m, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 167.0, 157.1, 147.7, 142.4, 140.5, 135.0, 134.5, 129.6, 121.8, 121.2, 120.1, 107.5, 64.4, 55.4, 30.8, 19.2, 13.7 ppm. IR (ZnSe): ν˜ = 2958, 2873, 1705, 1633, 1595, 1421, 1371, 1305, 1282, 1159, 1026, 985, 958, 862, 842, 783 cm–1. HRMS (EI): calcd. for C17H20NO3 [M + H]+ 286.1438; found 286.1422. Ethyl (E)-3-(6-Fluoroquinolin-8-yl)acrylate: (Table 2, compound 3n). Yellow resin (12.5 mg, 51 %). 1H NMR (600 MHz, CDCl3): δ = 8.94 (s, 1 H), 8.86 (d, J = 16.8 Hz, 1 H), 8.11 (d, J = 8.4 Hz, 1 H), 7.73 (d, J = 9.0 Hz, 1 H), 7.47 (d, J = 8.4 Hz, 2 H), 6.77 (d, J = 16.2 Hz, 1 H), 4.30–4.33 (m, 2 H), 1.37 (t, J = 7.2 Hz, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 166.6, 159.9 (d, J = 264.0 Hz), 149.5 (d, J = 1.5 Hz), 143.4, 139.6, 136.0 (d, J = 9.0 Hz), 135.6 (d, J = 6.0 Hz), 129.4 (d, J = 9.0 Hz), 122.3 (d, J = 48.0 Hz), 117.4 (d, J = 25.5 Hz), 112.7 (d, J = 21.0 Hz), 60.6, 14.3 ppm. IR


Eur. J. Org. Chem. 2015, 7519–7528

RhIII-Catalyzed Dehydrogenative Coupling of Quinoline N-Oxides (ZnSe): ν˜ = 2950, 1705, 1633, 1604, 1494, 1367, 1307, 1261, 1232, 1172, 1035, 983, 858, 785 cm–1. HRMS (EI): calcd. for C14H13FNO2 [M + H]+ 246.0925; found 246.0912. Ethyl (E)-3-[(4-Acetoxymethyl)quinolin-8-yl]acrylate: (Table 2, compound 3p). Orange semisolid (14.4 mg, 48 %). 1H NMR (300 MHz, CDCl3): δ = 8.93–9.00 (m, 2 H), 8.00–8.04 (m, 2 H), 7.64 (t, J = 7.8 Hz, 1 H), 7.52 (d, J = 3.9 Hz, 1 H), 6.79 (d, J = 16.2 Hz, 1 H), 5.61 (s, 2 H), 4.30–4.37 (m, 2 H), 2.21 (s, 3 H), 1.37–1.42 (m, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 170.4, 166.9, 149.9, 146.1, 141.0, 134.0, 127.7, 126.7, 126.1, 124.9, 120.9, 120.2, 62.5, 60.5, 20.7, 14.3 ppm. IR (ZnSe): ν˜ = 2918, 1741, 1732, 1710, 1631, 1573, 1363, 1307, 1224, 1172, 1047, 1029, 977, 840, 759 cm–1. HRMS (EI): calcd. for C17H18NO4 [M + H]+ 300.1230; found 300.1218. Ethyl (E)-3-(4-Formylquinolin-8-yl)acrylate: (Table 2, compound 3q). White solid (13.5 mg, 53 %); m.p. 72 °C. 1H NMR (600 MHz, CDCl3): δ = 10.53 (s, 1 H), 9.29 (d, J = 3.6 Hz, 1 H), 9.11 (d, J = 8.4 Hz, 1 H), 8.97 (d, J = 16.2 Hz, 1 H), 8.11 (d, J = 7.2 Hz, 1 H), 7.87 (d, J = 3.6 Hz, 1 H), 7.78 (t, J = 7.8 Hz, 1 H), 6.79 (d, J = 16.2 Hz, 1 H), 4.33–4.36 (m, 2 H), 1.41 (t, J = 7.2 Hz, 3 H) ppm. 13C NMR (151 MHz, CDCl3): δ = 192.7, 166.8, 150.1, 147.0, 140.6, 136.8, 133.7, 129.1, 128.1, 126.4, 126.2, 124.0, 121.2, 60.6, 14.4 ppm. IR (ZnSe): ν˜ = 2924, 2850, 1708, 1697, 1629, 1307, 1253, 1172, 1145, 1033, 989, 927, 862, 819, 759 cm–1. HRMS (EI): calcd. for C15H14NO3 [M + H]+ 256.0968; found 256.0955. Methyl (E)-8-(3-Ethoxy-3-oxoprop-1-enyl)quinoline-6-carboxylate: (Table 2, compound 3r). Light yellow solid (18.8 mg, 66 %); m.p. 102 °C. 1H NMR (600 MHz, C3D6O): δ = 9.11 (dd, J = 4.2, 1.8 Hz, 1 H), 8.91 (d, J = 16.2 Hz, 1 H), 8.69 (d, J = 1.8 Hz, 1 H), 8.62 (d, J = 1.2 Hz, 1 H), 8.57 (dd, J = 8.4, 1.8 Hz, 1 H), 7.70 (q, J = 4.2 Hz, 1 H), 6.96 (d, J = 16.8 Hz, 1 H), 4.27 (q, J = 7.2 Hz, 2 H), 3.98 (s, 3 H), 1.33 (t, J = 7.2 Hz, 3 H) ppm. 13C NMR (150 MHz, C3D6O): δ = 166.1, 165.6, 152.6, 147.4, 139.6, 137.9, 133.1, 132.5, 127.9, 127.9, 126.7, 122.7, 121.1, 60.0, 51.9, 13.7 ppm. IR (ZnSe): ν˜ = 3001, 2991, 1716, 1637, 1433, 1382, 1307, 1253, 1172, 1029, 989, 902, 860 cm–1. HRMS (EI): calcd. for C16H16NO4 [M + H]+ 286.1074; found 286.1059. Methyl (E)-8-[3-(Benzyloxy)-3-oxoprop-1-enyl]quinoline-6-carboxylate: (Table 2, compound 3s). Light yellow resin (20.0 mg, 58 %). 1H NMR (600 MHz, CDCl3): δ = 9.08 (s, 1 H), 8.95 (d, J = 16.2 Hz, 1 H), 8.61 (d, J = 16.1 Hz, 2 H), 8.29 (d, J = 8.1 Hz, 1 H), 7.59– 7.50 (m, 1 H), 7.47 (t, J = 17.5 Hz, 3 H), 7.40 (dt, J = 31.5, 7.2 Hz, 3 H), 7.38–7.29 (m, 2 H), 6.99 (d, J = 16.2 Hz, 1 H), 5.34 (s, 2 H), 4.03 (s, 3 H) ppm. 13C NMR (151 MHz, CDCl3): δ = 166.6, 166.1, 152.2, 147.8, 140.8, 137.5, 136.1, 133.6, 132.5, 128.5, 128.3, 128.2, 127.8, 127.7, 127.5, 122.3, 121.4, 66.4, 52.6 ppm. IR (ZnSe): ν˜ = 2954, 2922, 2852, 1708, 1595, 1492, 1454, 1421, 1375, 1213, 1157, 1132, 1045, 1026, 962, 842, 732 cm–1. HRMS (EI): calcd. for C21H18NO4 [M + H]+ 348.1230l; found 348.1251. Ethyl (E)-3-[3-(1,3-Dioxolan-2-yl)quinolin-8-yl]acrylate: (Table 2, compound 3t). Light yellow semisolid (10.2 mg, 41 %). 1H NMR (600 MHz, CDCl3): δ = 10.28 (s, 1 H), 9.42 (s, 1 H), 9.07 (s, 1 H), 8.89 (d, J = 16.2 Hz, 2 H), 8.64 (s, 1 H), 8.24 (s, 1 H), 8.13 (d, J = 7.2 Hz, 1 H), 7.99–8.03 (m, 2 H), 7.88 (d, J = 7.8 Hz, 1 H), 7.67– 7.70 (m, 1 H), 7.58 (t, J = 7.8 Hz, 1 H), 6.82 (d, J = 16.2 Hz, 2 H), 6.06 (s, 1 H), 4.29–4.34 (m, 4 H), 4.17–4.19 (m, 2 H), 4.11–4.13 (m, 2 H), 1.36–1.39 (m, 6 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 190.6, 167.1, 149.0, 148.9, 146.4, 140.8, 140.1, 139.9, 134.1, 133.2, 131.3, 131.2, 130.7, 130.2, 129.7, 128.8, 128.3, 127.6, 127.6, 126.6, 121.6, 120.9, 117.2, 102.0, 65.5, 60.6, 60.5, 14.4, 14.3 ppm. IR (ZnSe): ν˜ = 2927, 2854, 1697, 1633, 1573, 1492, 1365, 1305, 1226, Eur. J. Org. Chem. 2015, 7519–7528

1166, 1087, 1026, 991, 767 cm–1. HRMS (EI): calcd. for C17H18NO4 [M + H]+ 300.1230; found 300.1209. Ethyl (E)-3-(Acridine-4-yl)acrylate: (Table 2, compound 3u). Yellow resin (14.6 mg, 48 %). 1H NMR (600 MHz, CDCl3): δ = 9.04 (d, J = 16.2 Hz, 1 H), 8.69 (s, 1 H), 8.30 (d, J = 8.4 Hz, 1 H), 8.02 (d, J = 6.6 Hz, 1 H), 7.94–7.98 (q, J = 8.4 Hz, 2 H), 7.77–7.79 (m, 1 H), 7.48–7.54 (m, 2 H), 7.05 (d, J = 16.2 Hz, 1 H), 4.29–4.31 (m, 2 H), 1.74–1.79 (m, 2 H), 1.47–1.54 (m, 2 H), 1.00–1.02 (m, 3 H) ppm. 13 C NMR (150 MHz, CDCl3): δ = 167.5, 148.7, 146.8, 141.5, 136.2, 132.9, 130.4, 130.1, 129.2, 127.9, 126.5, 126.1, 125.2, 120.7, 64.4, 30.9, 19.3, 13.8 ppm. IR (ZnSe): ν˜ = 2968, 2872, 1705, 1629, 1519, 1327, 1303, 1166, 1028, 856, 773, 738 cm–1. HRMS (EI): calcd. for C20H20NO2 [M + H]+ 306.1489; found 306.1455. Ethyl (E)-3-(Phenanthridin-4-yl)acrylate: (Table 2, compound 3v). Pale yellow needles (14.9 mg, 54 %); m.p. 136 °C. 1H NMR (600 MHz, CDCl3): δ = 9.35 (s, 1 H), 9.09 (d, J = 16.2 Hz, 1 H), 8.62–8.65 (m, 2 H), 8.09 (d, J = 8.4 Hz, 1 H), 8.02 (d, J = 7.2 Hz, 1 H), 7.88–7.90 (m, 1 H), 7.74–7.76 (m, 1 H), 7.69–7.71 (m, 1 H), 6.74 (d, J = 16.2 Hz, 1 H), 4.33 (q, J = 7.2 Hz, 2 H), 1.38–1.40 (t, J = 7.2 Hz, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 167.1, 153.2, 153.1, 141.5, 133.8, 132.4, 131.1, 128.8, 127.8, 126.7, 126.3, 124.4, 124.2, 124.1, 122.0, 120.4, 60.5, 14.4 ppm. IR (ZnSe): ν˜ = 2950, 1710, 1633, 1309, 1267, 1226, 1170, 1151, 1029, 993, 862, 758, 738 cm–1. HRMS (EI): calcd. for C18H16NO2 [M + H]+ 278.1176; found 278.1141. General Procedure for C-8 Olefination of Quinoline N-Oxides with Styrenes and Aliphatic Olefins: To an oven-dried screw-cap reaction vial that was charged with a Spinvane magnetic stirring bar were added [Cp*RhCl2]2 (5 mol-%), AgSbF6 (20 mol-%), and Cu(OAc)2 (0.10 mmol). The mode of the addition for the quinoline N-oxide (0.10 mmol) and olefin (0.15 mmol) was determined by their physical state. Solid compounds were weighed along with the other reagents, whereas the liquid reagents and AcOH (0.05 mmol) were added by microliter syringe followed by the addition of DMF (0.2 m). The reaction vial was closed with a screw cap, and the reaction mixture was continuously stirred in a preheated oil bath or heating block at 100 °C for 24 h. Upon completion, the reaction mixture was extracted with ethyl acetate. The organic layer was dried with anhydrous Na2SO4 and concentrated under reduced pressure. The residue was purified by flash chromatography on silica gel (230–400 mesh; n-hexane/EtOAc). (E)-8-Styrylquinoline: (Table 3, compound 5a).[18c] Yellow needles (18.0 mg, 78 %); m.p. 97 °C. 1H NMR (300 MHz, CDCl3): δ = 8.98 (d, J = 3.6 Hz, 1 H), 8.51 (d, J = 16.5 Hz, 1 H), 8.15 (d, J = 8.1 Hz, 1 H), 8.06 (d, J = 7.2 Hz, 1 H), 7.68–7.76 (m, 3 H), 7.54–7.59 (m, 1 H), 7.28–7.45 (m, 5 H) ppm. 13C NMR (75 MHz, CDCl3): δ = 149.4, 146.0, 137.8, 136.2, 136.1, 130.6, 129.0, 128.5, 128.0, 127.6, 127.2, 126.9, 126.4, 125.2, 124.7, 121.1 ppm. IR (ZnSe): ν˜ = 2918, 2850, 1726, 1593, 1568, 1492, 1381, 1155, 964, 821, 786, 748, 690 cm–1. HRMS (EI): calcd. for C17H14N [M + H]+ 232.1121; found 232.1109. (E)-6-Methyl-8-(4-methylstyryl)quinoline: (Table 3, compound 5b). Yellow resin (16.6 mg, 64 %). 1H NMR (600 MHz, CDCl3): δ = 8.88 (d, J = 3.6 Hz, 1 H), 8.38 (d, J = 16.8 Hz, 1 H), 8.04 (d, J = 7.8 Hz, 1 H), 7.87 (s, 1 H), 7.56 (d, J = 7.8 Hz, 2 H), 7.48 (s, 1 H), 7.36 (q, J = 4.2 Hz, 1 H), 7.31 (d, J = 16.2 Hz, 1 H), 7.17 (d, J = 7.8 Hz, 2 H), 2.55 (s, 3 H), 2.35 (s, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 148.6, 144.6, 137.4, 136.1, 135.7, 135.6, 135.0, 130.3, 129.3, 128.6, 127.2, 126.9, 126.1, 123.5, 121.1, 21.7, 21.3. IR (ZnSe): ν˜ = 2922, 2854, 1593, 1512, 1489, 1365, 1180, 968, 850, 777 cm–1. HRMS (EI): calcd. for C19H18N [M + H]+ 260.1434; found 260.1461.


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(E)-6-Chloro-8-(4-methylstyryl)quinoline: (Table 3, compound 5c). Orange semisolid (11.5, 41 %). 1H NMR (600 MHz, CDCl3): δ = 8.94 (t, J = 1.8 Hz, 1 H), 8.37 (d, J = 16.8 Hz, 1 H), 8.05 (d, J = 8.4 Hz, 1 H), 7.97 (s, 1 H), 7.69 (s, 1 H), 7.58 (d, J = 7.8 Hz, 2 H), 7.43–7.45 (m, 1 H), 7.33 (d, J = 16.2 Hz, 1 H), 7.20 (d, J = 7.8 Hz, 2 H), 2.38 (s, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 149.5, 144.3, 138.2, 138.0, 135.3, 134.5, 131.8, 129.4, 129.3, 127.0, 125.5, 125.2, 122.2, 122.0, 21.3 ppm. IR (ZnSe): ν˜ = 2958, 1587, 1512, 1483, 1363, 1271, 1259, 1072, 1031, 970, 864, 779 cm–1. HRMS (EI): calcd. for C18H15ClN [M + H]+ 280.0888; found 280.0863.

(E)-2-Methyl-8-(4-nitrostyryl)quinoline: (Table 3, compound 5i). Green solid (18.9 mg, 65 %); m.p. 133 °C. 1H NMR (600 MHz, CDCl3): δ = 8.70 (d, J = 16.8 Hz, 1 H), 8.24 (d, J = 8.4 Hz, 2 H), 8.04 (t, J = 9.0 Hz, 2 H), 7.76–7.78 (m, 3 H), 7.50–7.53 (m, 1 H), 7.43 (d, J = 16.2 Hz, 1 H), 7.34 (d, J = 8.4 Hz, 1 H), 2.80 (s, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 158.7, 146.7, 145.5, 144.6, 136.3, 133.9, 129.8, 128.3, 127.6, 127.2, 126.7, 125.9, 125.4, 124.0, 122.2, 25.7 ppm. IR (ZnSe): ν˜ = 2912, 1589, 1334, 1031, 790, 744 cm–1. HRMS (EI): calcd. for C18H14N2O2 [M + H]+ 291.1128; found 291.1115.

(E)-2-Methyl-8-styrylquinoline: (Table 3, compound 5d). Green solid (10.5 mg, 45 %); m.p. 81 °C. 1H NMR (600 MHz, CDCl3): δ = 8.52 (d, J = 1.8 Hz, 1 H), 8.02 (d, J = 0.6 Hz, 2 H), 7.67–7.69 (m, 3 H), 7.48 (t, J = 0.6 Hz, 1 H), 7.35–7.40 (m, 3 H), 7.25–7.30 (m, 2 H), 2.78 (s, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 158.4, 145.6, 138.2, 136.3, 135.3, 130.2, 128.7, 127.6, 127.1, 127.0, 126.8, 125.6, 125.2, 125.1, 25.8 ppm. IR (ZnSe): ν˜ max = 2922, 2854, 1608, 1498, 1317, 1222, 966, 792, 744 cm–1. HRMS (EI): calcd. for C18H16N [M + H]+ 246.1277; found 246.1256.

(E)-4-[2-(2-Methylquinolin-8-yl)vinyl]benzonitrile: (Table 3, compound 5j). Green solid (18.4 mg, 68 %); m.p. 62 °C. 1H NMR (600 MHz, CDCl3): δ = 8.64 (d, J = 16.2 Hz, 1 H), 8.00–8.04 (m, 2 H), 7.70–7.75 (m, 1 H), 7.64 (d, J = 7.8 Hz, 2 H), 7.49–7.51 (m, 2 H), 7.36 (d, J = 16.8 Hz, 1 H), 7.31 (d, J = 8.4 Hz, 2 H), 2.79 (s, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 158.6, 145.5, 142.5, 136.3, 134.1, 132.4, 128.9, 128.1, 128.0, 127.2, 126.7, 125.7, 125.4, 122.2, 119.2, 110.3, 25.7 ppm. IR (ZnSe): ν˜ = 2945, 1598, 1504, 1031, 970, 835, 758 cm–1. HRMS (EI): calcd. for C19H15N2 [M + H]+ 271.1230; found 271.1214.

(E)-8-(4-Methoxystyryl)-2-methylquinoline: (Table 3, compound 5e). Green solid (12.9 mg, 47 %); m.p. 111 °C. 1H NMR (600 MHz, CDCl3): δ = 8.40 (d, J = 16.8 Hz, 1 H), 7.98–8.02 (m, 2 H), 7.66 (d, J = 8.4 Hz, 1 H), 7.62 (d, J = 7.8 Hz, 2 H), 7.47 (t, J = 7.8 Hz, 1 H), 7.28–7.34 (m, 2 H), 6.94 (d, J = 7.8 Hz, 2 H), 3.05 (s, 3 H), 2.79 (s, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 159.2, 158.1, 145.4, 136.2, 135.5, 131.0, 129.6, 128.1, 126.7, 126.6, 125.4, 124.7, 122.8, 122.0, 121.9, 114.0, 55.3, 25.6 ppm. IR (ZnSe): ν˜ = 2927, 2852, 1726, 1602, 1498, 1454, 1265, 1242, 1172, 1029, 958, 829, 763 cm–1. HRMS (EI): calcd. for C19H18NO [M + H]+ 276.1383; found 276.1365. (E)-8-(4-Bromostyryl)-2-methylquinoline: (Table 3, compound 5f). White solid (11.7 mg, 36 %); m.p. 104 °C. 1H NMR (600 MHz, CDCl3): δ = 8.52 (d, J = 16.8 Hz, 1 H), 7.99–8.03 (m, 1 H), 7.70 (d, J = 7.8 Hz, 1 H), 7.48–7.54 (m, 5 H), 7.29 (d, J = 5.4 Hz, 2 H), 2.79 (s, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 158.4, 145.4, 137.0, 136.2, 134.8, 131.7, 128.7, 128.7, 128.4, 128.0, 127.3, 126.7, 125.7, 125.4, 125.2, 122.0, 121.2, 25.7 ppm. IR (ZnSe): ν˜ = 2999, 2922, 2846, 1597, 1485, 1325, 1070, 1029, 1008, 964, 831, 759 cm–1. HRMS (EI): calcd. for C18H15BrN [M + H]+ 324.0382; found 324.0365. (E)-4-[2-(2-Methylquinoline-8-yl)vinyl]phenol: (Table 3, compound 5g). Green solid (12.3 mg, 47 %); m.p. 174 °C. 1H NMR (600 MHz, CDCl3): δ = 8.27 (d, J = 16.2 Hz, 1 H), 8.05 (d, J = 8.4 Hz, 1 H), 7.96 (d, J = 7.2 Hz, 1 H), 7.68 (d, J = 8.4 Hz, 1 H), 7.48 (t, J = 7.8 Hz, 1 H), 7.44 (d, J = 7.8 Hz, 2 H), 7.31 (d, J = 8.4 Hz, 1 H), 7.23 (d, J = 16.8 Hz, 1 H), 6.83 (d, J = 7.8 Hz, 2 H), 2.81 (s, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 158.4, 155.6, 145.3, 136.6, 135.7, 130.8, 130.2, 128.2, 126.7, 126.6, 125.6, 125.2, 122.9, 122.1, 115.6, 25.4 ppm. IR (ZnSe): ν˜ = 2924, 2854, 1598, 1512, 1433, 1359, 1166, 972, 831, 759 cm–1. HRMS (EI): calcd. for C18H15NO [M + H]+ 262.1226; found 262.1205. (E)-Methyl 4-[2-(2-Methylquinolin-8-yl)vinyl]benzoate: (Table 3, compound 5h). Green solid (16.4 mg, 54 %); m.p. 71 °C. 1H NMR (600 MHz, CDCl3): δ = 8.64 (d, J = 16.2 Hz, 1 H), 8.04 (d, J = 7.8 Hz, 2 H), 8.02–8.03 (m, 2 H), 7.71 (d, J = 7.8 Hz, 3 H), 7.48– 7.50 (m, 1 H), 7.40 (d, J = 16.2 Hz, 1 H), 7.31 (d, J = 8.4 Hz, 1 H), 3.93 (s, 3 H), 2.80 (s, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 167.0, 158.5, 145.5, 142.6, 136.2, 134.6, 129.9, 129.8, 129.4, 128.9, 128.9, 128.7, 127.7, 127.7, 126.7, 125.5, 125.4, 122.1, 52.0, 25.6 ppm. IR (ZnSe): ν˜ = 2912, 2852, 1710, 1600, 1500, 1435, 1276, 1257, 1174, 1109, 989, 827, 750 cm–1. HRMS (EI): calcd. for C20H18NO2 [M + H]+ 304.1332; found 304.1309. 7526

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(E)-8-[2-(Biphenyl-4-yl)vinyl]-2-methylquinoline: (Table 3, compound 5k). Green solid (15.4 mg, 48 %); m.p. 150 °C. 1H NMR (600 MHz, CDCl3): δ = 8.67 (d, J = 16.2 Hz, 1 H), 8.09 (d, J = 7.2 Hz, 1 H), 8.06 (d, J = 8.4 Hz, 1 H), 7.81 (d, J = 7.8 Hz, 2 H), 7.76–7.68 (m, 5 H), 7.56–7.48 (m, 4 H), 7.42 (t, J = 7.2 Hz, 1 H), 7.34 (d, J = 8.4 Hz, 1 H), 2.87 (s, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 158.3, 145.5, 140.8, 140.1, 137.2, 136.3, 135.2, 129.6, 128.8, 127.4, 127.3, 127.1, 126.9, 126.7, 125.5, 125.2, 125.1, 25.7 ppm. IR (ZnSe): ν˜ = 2933, 2864, 1604, 1485, 1467, 1255, 1031, 979, 837, 758 cm–1. HRMS (EI): calcd. for C24H20N [M + H]+ 322.1590; found 322.1581. (E)-2-Methyl-8-[2-(naphthalen-2-yl)vinyl]quinoline: (Table 3, compound 5l). Green solid (15.2 mg, 41 %); m.p. 109 °C. 1H NMR (600 MHz, CDCl3): δ = 8.70 (d, J = 16.2 Hz, 1 H), 8.09 (d, J = 7.2 Hz, 1 H), 8.03 (d, J = 8.4 Hz, 1 H), 7.99–7.97 (m, 2 H), 7.88 (d, J = 8.4 Hz, 2 H), 7.85 (d, J = 7.8 Hz, 1 H), 7.71 (d, J = 6.6 Hz, 1 H), 7.56 (d, J = 16.8 Hz, 1 H), 7.54–7.47 (m, 3 H), 7.32 (d, J = 8.4 Hz, 1 H), 2.84 (s, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 158.35, 145.53, 136.30, 135.70, 135.70, 135.23, 133.82, 133.13, 130.19, 128.21, 128.10, 127.75, 127.16, 126.91, 126.77, 126.23, 125.81, 125.54, 125.37, 125.18, 124.20, 122.05, 25.76 ppm. IR (ZnSe): ν˜ = 2912, 2845, 1598, 1504, 1371, 1319, 1222, 1031, 974, 790, 736 cm–1. HRMS (EI): calcd. for C22H18N [M + H]+ 296.1434; found 296.1421. (E)-2-Methyl-8-(oct-1-enyl)quinoline: (Table 4, compound 7a). Green resin (13.2 mg, 37 %). 1H NMR (600 MHz, CDCl3): δ = 7.99 (d, J = 8.4 Hz, 1 H), 7.84 (d, J = 7.2 Hz, 1 H), 7.73 (d, J = 16.2 Hz, 1 H), 7.62 (d, J = 7.8 Hz, 1 H), 7.42 (t, J = 7.8 Hz, 1 H), 7.25–7.26 (m, 1 H), 6.47–6.52 (m, 1 H), 2.76 (s, 3 H), 2.38 (dd, J = 14.7, 7.2 Hz, 2 H), 1.53–1.58 (m, 2 H), 1.39–1.44 (m, 3 H), 1.33–1.35 (m, 4 H), 0.90–0.93 (m, 3 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 158.0, 145.1, 136.1, 135.7, 132.9, 126.6, 126.2, 125.6, 125.4, 124.9, 121.3, 33.7, 31.9, 29.3, 28.8, 25.5, 22.4, 14.1 ppm. IR (ZnSe): ν˜ = 2954, 2918, 2854, 1612, 1598, 1566, 1500, 1460, 1325, 1224, 972, 758 cm–1. HRMS (EI): calcd. for C18H24N [M + H]+ 254.1903; found 254.1897. (E)-8-(3-Cyclohexylprop-1-enyl)-2-methylquinoline: (Table 4, compound 7b). Green resin (14.7 mg, 40 %). 1H NMR (600 MHz, CDCl3): δ = 7.84 (d, J = 8.4 Hz, 1 H), 7.71 (d, J = 7.2 Hz, 1 H), 7.56 (d, J = 15.6 Hz, 1 H), 7.47 (d, J = 7.8 Hz, 1 H), 7.27 (t, J = 7.8 Hz, 1 H), 7.11 (d, J = 8.4 Hz, 1 H), 6.40–6.32 (m, 1 H), 2.62 (s, 3 H), 2.14 (t, J = 7.2 Hz, 2 H), 1.69 (d, J = 15.0 Hz, 2 H), 1.53


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RhIII-Catalyzed Dehydrogenative Coupling of Quinoline N-Oxides (d, J = 12.6 Hz, 1 H), 1.35 (s, 1 H), 1.13 (d, J = 7.8 Hz, 3 H), 0.91– 0.853 (m, 2 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 158.0, 145.1, 136.1, 135.7, 131.5, 126.6, 126.5, 126.2, 125.4, 124.9, 121.7, 41.5, 38.4, 33.3, 26.6, 26.4, 25.7 ppm. IR (ZnSe): ν˜ = 2916, 2850, 1612, 1598, 1500, 1446, 1431, 1136, 974, 835, 758 cm–1. HRMS (EI): calcd. for C19H24N [M + H]+ 266.1903; found 266.1895. General Procedure for the Synthesis of Rhodacycle A: To a screwcap vial that was charged with a Spinvane triangular stirring bar were added quinoline N-oxide (0.5 mmol), [Cp*RhCl2]2 (0.25 mmol), NaOAc (3 equiv.), and CH3OH (2.5 mL). The reaction mixture was stirred at room temp. for 5 h and then heated at 100 °C for 13 h. Upon completion, the reaction mixture was filtered, and the filter cake was washed with ethyl acetate. The filtrate was concentrated under reduced pressure, and the residue was purified by flash chromatography on silica gel (petroleum ether/ethyl acetate). Rhodacycle A: (Scheme 6, a). Orange needles (33.3 mg, 16 %). 1H NMR (600 MHz, CDCl3): δ = 8.46 (d, J = 6.0 Hz, 1 H), 8.01 (d, J = 6.6 Hz, 1 H), 7.78 (d, J = 8.4 Hz, 1 H), 7.53 (t, J = 7.8 Hz, 1 H), 7.42 (d, J = 8.4 Hz, 1 H), 7.19–7.21 (m, 1 H), 1.70 (s, 15 H) ppm. 13C NMR (150 MHz, CDCl3): δ = 166.2 (d, 1JRh,C = 78.6 Hz), 146.6, 136.3, 133.4, 130.7, 130.4, 129.9, 121.0, 119.4, 94.7 (d, 1JRh,C = 7.35 Hz, 5 C, C5Me5), 9.1 ppm. IR (ZnSe): ν˜ = 2922, 2845, 1737, 1658, 1568, 1442, 1390, 1305, 1265, 1226, 1136, 1026, 918, 881, 796, 767 cm–1. HRMS: calcd. for C19H21NORh [M – Cl] 382.0678; found 382.0645. CCDC-1407132 (for 3h), -1407233 (for 3v), -1407129 (for 5a), -1407128 (for 5j), -1407130 (for 5k), and -1407799 (for rhodacycle A) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/ data_request/cif. Supporting Information (see footnote on the first page of this article): Optimization studies, characterization data of all synthesized compounds including 1H and 13C NMR spectra as well as X-ray data for 3h, 3v, 5a, 5j, 5k, and rhodacycle A; experimental details of the mechanistic study.

Acknowledgments The authors are grateful to the Director of the Council of Scientific and Industrial Research-Institute of Himalayan Bioresource Technology (CSIR-IHBT) and the CSIR, India for providing necessary facilities during this work. This activity was supported by the Science and Engineering Research Board, India (EMR/2014/001023). R. K. and I. K. acknowledge the University Grants Commission (UGC), New Delhi for Junior Research fellowships. The authors thank Mr. Puneet Sood, Indian Institute of Technology (IIT) Mandi, for the X-ray analysis. The CSIR-IHBT communication no. for this manuscript is 3881. [1] a) D. A. Colby, R. G. Bergman, J. A. Ellman, Chem. Rev. 2010, 110, 624–655; b) T. W. Lyons, M. S. Sanford, Chem. Rev. 2010, 110, 1147–1169; c) W. R. Gutekunst, P. S. Baran, Chem. Soc. Rev. 2011, 40, 1976–1991; d) L. Ackermann, Chem. Rev. 2011, 111, 1315–1345; e) J. Wencel-Delord, T. Droge, F. Liu, F. Glorius, Chem. Soc. Rev. 2011, 40, 4740–4761. [2] a) R. J. Phipps, M. J. Gaunt, Science 2009, 323, 1593–1597; b) D. Leow, G. Li, T.-S. Mei, J.-Q. Yu, Nature 2012, 486, 518– 522; c) R.-Y. Tang, G. Li, J.-Q. Yu, Nature 2014, 507, 215–220; d) J. Schranck, A. Tlili, M. Beller, Angew. Chem. Int. Ed. 2014, 53, 9426–9428; e) M. Á. Fernández-Ibáñez, ChemCatChem Eur. J. Org. Chem. 2015, 7519–7528

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