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Calcium mediated C–F bond substitution in fluoroarenes towards C–chalcogen bond formation† Pintu Maity,a Sabir Ahammed,b Rabindra Nath Mannac and Brindaban C. Ranu*a

Published on 20 October 2016. Downloaded on 02/11/2016 08:39:02.

A new calcium chloride mediated C–F bond cleavage in electron deficient fluoroarenes followed by Received 6th September 2016, Accepted 18th October 2016

functionalisation via C–Se/Te bond formation has been achieved in the absence of any additive/ligand/

DOI: 10.1039/c6qo00515b

organometallic reagent. A series of functionalised organo-selenides and -tellurides were obtained in high yields by this procedure. The precise role of calcium and the possible mechanism have been proposed

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based on DFT analysis.

Introduction The C–F bond dissociation energy is the largest among all other C–X bonds (X = halogen).1 Moreover, the reluctance of the C–F moiety to co-ordinate with the metal centres makes the C–F bond relatively inert2 and thus cleavage of a C–F bond towards further functionalisation is a challenging task. In practice, the activation of a C–F moiety is initiated either by reductive cleavage of the C–F bond by a low valent transition metal3 or intermolecular hydrogen–fluorine exchange mediated by a trivalent organolanthanide complex.4 Several reports of C–F bond activation in fluoroarenes towards C–C bond formation catalyzed by Pd- and Ni-complexes are also available.3 Besides the transition metals, the use of group 2 alkaline earth metals such as calcium, strontium and barium have also been reported for specific organic transformations. These elements show excellent Lewis acid property because of their large radii and electropositive character. In addition to these, their low toxicity and cost efficiency have made them more attractive to be explored for new reactions. Recently calcium complexes have been reported to be employed for different types of organic reactions such as alkene hydroamination,5 hydrophosphonations,6 Michael reaction,7 aldol condensation,8 epoxidation,9 Tishchenko reactions,10 Sonogashira reaction,11 Pictet Spengler reactions,12 Friedel Crafts alkylation,13 cyclopropanation,14 dynamic multicomponent reaction,15 intermolecular

a Department of Organic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India. E-mail: [email protected] b Department of Chemistry, Aliah University, IIA/27, Action Area II, Newtown, Kolkata 700156, India c Department of Physical Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India † Electronic supplementary information (ESI) available: 1H NMR, 13C NMR spectra of all the synthesized compounds and DFT calculation data. See DOI: 10.1039/c6qo00515b

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carbohydroxylation of alkynes etc.16 Shu Kobayashi and others have applied chiral complexes of calcium in an enantioselective process too.17 Recently Hill and co-workers demonstrated the use of a calcium β-diketiminate complex for C–F bond cleavage via an intermediate heteroleptic calcium fluoride complex.18 To add a simpler procedure we report here a calcium chloride mediated C–F bond cleavage in electron deficient fluoroarenes for C–Se and C–Te functionalisation in the absence of any additive and ligand leading to the synthesis of a series of organoselenides and tellurides (Scheme 1a). Nevertheless, zinc dust has been used to cleave the Se–Se/ Te–Te bond to make the PhSe/PhTe moiety available for the reaction and in no way has any role in C–F bond cleavage. To the best of our knowledge we are not aware of any direct Camediated defluorination of fluoroarenes towards functionalisation in the absence of any additive/ligand/base. However, one report for Sonogashira-type cross-coupling of alkynes with fluoroarenes in the presence of excess sodium, NaOMe, Ca(OH)2 and n-butylmagnesium chloride was found (Scheme 1b).11 Needless to say, the organoselenides are of much importance and of continued interest because of their presence as

Scheme 1

Calcium mediated C–F bond activation.

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structural motifs in a variety of molecules of biological, pharmaceutical and material interest.19 They are used as catalysts for various reactions such as oxyselenation–elimination and valuable intermediates in organic synthesis.20 Thus a number of methods have been developed for their synthesis.21 These include transition metal catalyzed C–Se bond formation through cross coupling of aryl halides (mainly I, Br, Cl), aryl boronic acid, and aryl triflates with selenol/PhSeNa/diphenyl diselenides.22 Recently some metal free procedures23 (microwave irradiation, ball-milling, visible light photocatalysis etc.) have also been developed.


Results and discussion To optimise the reaction conditions, a series of experiments were performed under varying reaction parameters such as different metal salts, solvents, temperature and time for a representative reaction of 4-fluorobenzonitrile and diphenyl diselenide. Among a variety of metal salts and solvents studied, calcium chloride in DMSO is the most effective combination and the best result was observed in a reaction at 110 °C for 12 h in the presence of Zn dust (Table 1, entry 4). A reaction at lower temperature and reduced time decreased the yield (Table 1, entries 1–3). The reaction did not initiate in the presence of other metal salts such as MnCl2, SnCl2, ZnCl2, SbCl5, NiCl2, AgF and AgOAc (Table 1, entries 5–11). Other calcium salts such as CaCO3, Ca(OAc)2 and Ca(NO3)2 have been investigated and none of these is considerably efficient although only Ca(OAc)2 provides 25% yield (Table 1, entries 12–14). DMF and NMP are also effective for the reaction (Table 1, entries 15 and 16). The reaction did not proceed at all in other solvents such as H2O, dimethyl carbonate (DMC) and xylene under similar conditions (Table 1, entries 17, 19 and 20). However a trace amount of the product was observed in CH3CN (Table 1, entry 18). Instead of Zn, the use of KOH and indium as cleaving agents failed to produce the product (Table 1, entries 21 and 22). The reaction did not proceed in the absence of calcium chloride (Table 1, entry 24). A reduction of the amount of CaCl2 decreased the yield (Table 1, entries 25 and 26). The reaction produced lower yields of the product on using group 1 metal salts such as LiCl, NaCl, KCl and CsF instead of CaCl2 (Table 1, entries 27–30). Thus in a general experimental procedure a mixture of fluoroarene (1.0 mmol), diaryl diselenide (0.6 mmol), calcium chloride (3.0 mmol), and Zn dust (1.1 mmol) in DMSO (3 mL) was stirred under an argon atmosphere at 110 °C for 12 h. After evaporation of DMSO, the crude product was extracted with ethyl acetate. The pure product was isolated by column chromatography over silica gel. A wide range of diversely substituted diphenyl selenides have been obtained by this procedure. All the products are summarized in Table 2. Several (ten) of these compounds are reported for the first time. The fluoroarenes containing an electron withdrawing group (–NO2, –CN, –CHO, –COCH3, –COPh) underwent an efficient reaction with substituted diphenyl diselenides (–Me, –Cl,

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Organic Chemistry Frontiers Table 1

Optimisation of reaction conditionsa

Entry

Metal salt

Time (h)

Temp. (°C)

Solvent

Yieldb (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21c 22d 23e 24 25 f 26g 27 28 29 30

CaCl2 CaCl2 CaCl2 CaCl2 MnCl2 SnCl2 ZnCl2 SbCl5 NiCl2 AgF Ag(OAc) CaCO3 Ca(OAc)2 Ca(NO3)2 CaCl2 CaCl2 CaCl2 CaCl2 CaCl2 CaCl2 CaCl2 CaCl2 CaCl2 — CaCl2 CaCl2 LiCl NaCl KCl CsF

8 10 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12

100 100 100 110 110 110 110 110 110 110 110 110 110 110 110 110 110 110 110 110 110 110 110 110 110 110 110 110 110 110

DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMF NMP H2O CH3CN DMC Xylene DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO DMSO

45 57 65 92 — — — — — — — — 25 — 85 81 — Trace — — 11 — Trace — 65 84 31 12 15 38

a Reaction conditions: 4-fluorobenzonitrile (1.0 equiv.), diphenyl diselenide (0.6 equiv.), metal salt (3.0 equiv.), Zn dust (1.1 equiv.), argon atmosphere. b Isolated yield. c KOH (1.1 equiv.). d In (1.1 equiv.). e Without Zn dust. f Calcium salt (1.0 equiv.). g Calcium salt (2.0 equiv.).

–OMe) to afford the corresponding selenides (3a–u). The unsubstituted and electron donating group substituted fluoroarenes are not effective for this reaction. Perfluoroarenes such as hexafluorobenzene and octafluorotoluene also did not produce the corresponding product under standardized conditions. It may be due to the less electrophilic nature of the arenes as well as less nucleophilic nature of PhSe under our experimental conditions. The other halogen (Cl, Br, I) substituted arenes also remained inert under these conditions. The Cl-substituted diphenyl diselenide reacted in the usual way keeping the Cl group unaffected during the reaction (3e and 3s) and it may be used for further functionalisation. In addition, the other functionalities (–NO2, –CN, –CHO, –COCH3, –COPh) present in the selenide products may be of much importance for further derivatisation. For example, 2-nitrophenyl-phenyl selenide obtained from 1-fluoro-2-nitrobenzene was successfully converted to 2-furylphenyl-phenyl selenide 4a by manipulation of nitro functionality (Scheme 2).24a,b The unique feature of this protocol is the use of fluoroarenes for the C–Se bond formation involving diphenyl


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Table 2 Calcium mediated selenylation of fluoroarenes via C–F bond cleavagea,b


Scheme 3

a Reaction conditions: fluoroarenes (1.0 equiv.), diaryl diselenide (0.6 equiv.), calcium chloride (3.0 equiv.), Zn dust (1.1 equiv.), argon atmosphere, 12 h, 110 °C. b Isolated yield.

Scheme 2 Synthesis of 2-furylphenyl-phenyl selenide from 2-fluoronitrobenzene.

diselenide which was not addressed earlier except in one reaction with a specific substrate24c where the selenylation was performed using diphenyl diselenide and sodium borohydride. Notably, our method uses zinc dust and thus is compatible with reducible functionalities. Moreover, this has general applicability with all types of electron deficient fluoroarenes. This strategy is also applied for the synthesis of unsymmetrical diaryl tellurides (Scheme 3). In general we obtained relatively low yield in tellurides. This may be due to the low reactivity of tellurium species probably dictated by the larger size of Te. We then turned our attention to find the mechanism for this Ca-mediated selenylation reaction. To check the involvement of a radical process, the reaction of 4-fluoro benzonitrile and diphenyl diselenide was performed in the presence of TEMPO (radical quencher), THF (electron receptor), and


Calcium mediated C(sp2)–Te bond formation.

nitroarene (electron acceptor) separately. Notably, the reactions remained unaffected. So the possibility of a radical pathway is unlikely for this reaction. In this reaction, zinc dust has been used to cleave the Se–Se/Te–Te bond to make the PhSe/PhTe moiety available. It has been observed that no product was formed in the absence of calcium chloride (Table 1, entry 24). However, if a free nucleophile (PhSe/PhTe−) is available in the medium the reaction is expected to produce some amount of product. Thus the reaction is not likely to follow the classical Nucleophilic Aromatic Substitution (SNAr) pathway. To have a better understanding on the role of Ca in C–F bond cleavage the mechanism of the process has been investigated using quantum mechanical (QM) calculations. For this purpose, we have prepared six different models. Herein, models A, B, C, D and E denote 4-fluorobenzonitrile and Ph–Se–Zn–Se–Ph structures with Ca2+, without any metal cation, with Zn2+, with Ni2+ and with one explicit DMSO molecule ligating with Ca2+, respectively. On the other side, model F is represented by 4-fluorobenzonitrile and the Ph–Se–Ca–Se–Ph structure with a Ca2+ cation. The computational details of QM modeling approaches are described in the ESI.† Cyclic six membered transition state (TSA) structures for the formation of selenides are found more stable with lower activation free energy (ΔG‡ = 32.5 kcal mol−1) in the presence of Ca2+ than the four membered TSB (ΔG‡ = 41.1 kcal mol−1) structure obtained in the absence of metal salts. The C(sp2)–Se and C(sp2)–F bond distances for six membered TS structures for the models A, C, and D in the presence of Zn and metal salts (such as Ca2+, Zn2+, and Ni2+) are in the range of 2.77–2.94 Å and 1.84–2.18 Å, respectively. For the four membered TSB, C(sp2)–Se and C(sp2)–F bond distances are 2.37 and 1.70 Å, respectively, which are significantly shorter than the distances obtained from the six TS structures. On the other side, the predicted activation barriers for the formation of selenides in the presence of Zn2+ and Ni2+ are 37.4 and 35.1 kcal mol−1, respectively, at the SMDDMSO/ B3LYP/6-311+G(d,p) level of theory,25 which are significantly higher than the activation energy barrier (32.5 kcal mol−1) obtained in the presence of calcium metal salts. Moreover, Ca2+ having a vacant d orbital is a hard Lewis acid and possesses a high charge to size ratio whereas Zn2+ and Ni2+ are border line Lewis acids. According to the hard soft acid base principle, the hard Lewis base F− prefers to bind to the hard Lewis acid Ca2+ than other border line Lewis acids. Therefore, Ca2+ makes F− a good leaving group compared to the other metal salts which have been used in our studies. Hence, calcium salt mediated C–F bond cleavage for the formation of

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diaryl selenides is favorable than other metal salts. Our experimental results also showed this trend. However, the possibility of transmetallation during the reaction is also investigated. In the model F, transmetallation leads to a Ph–Se–Ca–Se–Ph type intermediate from Ph–Se–Zn–Se–Ph. Moreover, in the TSF structure, Se–Ca distances are significantly elongated (2.87 and 2.97 Å) compared to those in other TS structures (Fig. 1). The free energy of activation for the model F via TSF for the formation of selenides is 26.6 kcal mol−1 at the SMDDMSO/B3LYP/ 6-311+G(d,p) level of theory which is lower than the value derived from the other models (Fig. 2). Moreover, the C(sp2)–Se and C(sp2)–F bond distances in the TSE are 2.67 and 1.57 Å, respectively, which are slightly shorter than the aforementioned distances in the other TS structures. The computed reaction free energy along the model E is −28.6 kcal mol−1 which indicates that the formation of selenides is energetically favorable. According to our study, transmetallation helps to decrease the free energy barrier from 32.5 (model A) to 26.6 kcal mol−1 (model F). Therefore, our results show that for-


Fig. 2 Computed Gibbs free energy (in kcal mol−1) profiles for the C(sp2)–F bond activation in fluoroarenes via C(sp2)–Se bond formation are obtained using different models at the SMDDMSO/B3LYP/6-311+G(d,p) level of theory at 110 °C. Moreover, RS, TS and PS represented the reactant state, transition state and product state, respectively.

mation of diaryl selenides proceeds via the Ph–Se–Ca–Se–Ph intermediate than Ph–Se–Zn–Se–Ph. Furthermore, we have also explored the role of DMSO in the mechanism using model E, where one DMSO molecule possesses substantial ligating interaction with the Ca2+ metal centre. In the TSE, the DMSO molecule is interacting with the Ca2+ ion (Ca2+–O: 2.15 Å) although, the computed activation free energy for the model E is higher than the value obtained from the model F. Based on the results of the computational study we have proposed a possible reaction pathway (Scheme 4). In the first step diphenyl diselenide reacts with Zn dust to produce (PhSe)2Zn (A). Then the (PhSe)2Zn (A) interacts with calcium to give an intermediate (B) through transmetallation. Subsequently, (PhSe)2Ca reacts with electron deficient fluoroarene in the presence of calcium chloride to form the stable six membered transition state C which ultimately leads to the corresponding diphenyl selenide.

Fig. 1 Key geometrical distances (Å) of the TS structures from different models for the formation of selenides are obtained at the SMD(DMSO)B3LYP/6-311+G(d,p) level of theory at 110 °C.

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Scheme 4

Possible reaction pathway.


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Conclusion In conclusion, we have achieved direct calcium chloride mediated C–F bond activation in electron deficient fluoroarenes towards C–chalcogen bond formation in the absence of any additive/ligand leading to the synthesis of functionalised organo-selenides and tellurides. This protocol provides enormous scope for further manipulation to obtain new selenide derivatives. To the best of our knowledge this is the first report of C–F functionalisation of fluoroarenes using only Ca-salt in the absence of any strong base and organometallic reagent. The role of calcium in the cleavage of the C–F bond and the mechanism of the reaction has been established by using DFT analysis. This work thus opens a new vista for functionalisation of the apparently inert C–F bond by a simple operation using an inexpensive reagent, calcium chloride.

Experimental section General IR spectra were taken as thin films for liquid compounds and as KBr pellets for solids. NMR spectra were recorded at 300, 400 and 500 MHz for 1H NMR spectra and at 75, 100 and 125 MHz for 13C NMR spectra in CDCl3 solutions. HRMS analysis was performed in a Qtof mass analyzer using an ESI ionization method. Elemental analyses are done at our institute using an autoanalyser. The all substituted diaryl diselenides were synthesized using previously reported procedures.26e Representative experimental procedure for the synthesis of (2-nitrophenyl)(m-tolyl)selane (Table 2, 3a) A mixture of 2-fluoronitrobenzene (141 mg, 1.0 mmol), 3-methyl diphenyl diselenide (204 mg, 0.6 mmol), calcium chloride (333 mg, 3.0 mmol), and Zn dust (72 mg, 1.1 mmol) in DMSO (3 mL) was heated at 110 °C (bath temperature) for 12 h (TLC) in an oil bath under an argon atmosphere. The reaction mixture was then allowed to cool and DMSO was evaporated under vacuum. The residue was extracted with EtOAc (3 × 20 mL). The extract was washed with water (10 mL) and brine (10 mL). The organic phase was dried (Na2SO4) and evaporated to afford the crude product, which was purified by column chromatography over silica gel (hexane) to provide the pure (2-nitrophenyl)(m-tolyl)selane as a pale yellow solid (245 mg, 84%), mp 79–82 °C, 1H NMR (CDCl3, 300 MHz) δ 2.40 (s, 3H), 7.01–7.04 (m, 1H), 7.28–7.38 (m, 4H), 7.49–7.53 (m, 2H), 8.28–8.32 (m, 1H); 13C NMR (CDCl3, 75 MHz) δ 21.4, 125.8, 126.1, 127.9, 130.0, 130.4, 130.8, 133.7, 134.5, 136.2, 138.0, 140.1, 145.7; IR (KBr): 2984, 2883, 1587, 1512, 1330 cm−1; anal. calcd for C13H11NO2Se: C 53.44, H 3.79, N 4.79; found: C 53.42, H 3.82, N 4.75%. This procedure was followed for all the reactions listed in Table 2, Schemes 2 and 3. Many of these compounds have not been reported earlier and these unknown compounds were characterized suitably by their spectroscopic and spectrometric


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data (IR, 1H NMR, 13C NMR, HRMS and elemental analysis). The known compounds were identified by comparison of their spectroscopic and spectrometric data with those reported earlier. All these data are provided here. 2-((4-Methoxyphenyl)selanyl)benzonitrile (Table 2, 3b).26a (256 mg, 89%), 1H NMR (CDCl3, 300 MHz) δ 3.83 (s, 3H), 6.90–6.93 (m, 2H), 7.10–7.13 (m, 1H), 7.19–7.34 (m, 2H), 7.56–7.59 (m, 3H); 13C NMR (CDCl3, 75 MHz) δ 55.5, 113.5, 115.7 (2C), 117.5, 117.6, 126.4, 130.8, 133.0, 133.6, 138.1 (2C), 139.4, 160.8. 2-( p-Tolylselanyl)benzaldehyde (Table 2, 3c). Light red liquid (184 mg, 67%), 1H NMR (CDCl3, 300 MHz) δ 2.42 (s, 3H), 7.01–7.04 (m, 1H), 7.22–7.32 (m, 4H), 7.54–7.56 (m, 2H), 7.81–7.84 (m, 1H), 10.19 (s, 1H); 13C NMR (CDCl3, 75 MHz) δ 21.5, 124.5, 125.4, 129.9, 130.8 (2C), 133.9, 135.2, 137.0 (2C), 139.5, 140.3, 192.6; IR (neat): 3016, 2921, 1691, 1672, 1583, 1452, 1218 cm−1; anal. calcd for C14H12OSe: C 61.10, H 4.40; found: C 61.14, H 4.35%. 1-((4-Phenylselanyl)phenyl)ethanone (Table 2, 3d).23a (247.5 mg, 90%), 1H NMR (CDCl3, 300 MHz) δ 2.54 (s, 3H), 7.34–7.39 (m, 5H), 7.57–7.60 (m, 2H), 7.77–7.79 (m, 2H); 13 C NMR (CDCl3, 75 MHz) δ 26.5, 128.7, 128.9 (2C), 129.8 (2C), 130.4 (2C), 133.6, 135.2 (2C), 135.3, 140.3, 197.3. 4-((4-Chlorophenyl)selanyl)benzonitrile (Table 2, 3e).26d (255 mg, 87%), 1H NMR (CDCl3, 500 MHz) δ 7.34–7.37 (m, 4H), 7.48 (d, J = 8.5 Hz, 2H), 7.53 (d, J = 8.5 Hz, 2H); 13 C NMR (CDCl3, 125 MHz) δ 110.2, 118.7, 126.0, 130.3 (2C), 130.6 (2C), 132.6 (2C), 135.7, 136.9 (2C), 140.3. 4-( p-Tolylselanyl)benzonitrile (Table 2, 3f ).26d (247.5 mg, 91%), 1H NMR (CDCl3, 300 MHz) δ 2.39 (s, 3H), 7.20 (d, J = 7.8 Hz, 2H), 7.27–7.31 (m, 2H), 7.40–7.44 (m, 2H), 7.49–7.52 (m, 2H); 13C NMR (CDCl3, 75 MHz) δ 21.4, 109.4, 118.9, 123.6, 129.8 (2C), 130.9 (2C), 132.4 (2C), 136.1 (2C), 139.7, 141.8. 2-( p-Tolylselanyl)benzonitrile (Table 2, 3g).23a (220 mg, 81%), 1H NMR (CDCl3, 300 MHz) δ 2.38 (s, 3H), 7.17–7.34 (m, 4H), 7.50–7.52 (m, 2H), 7.58–7.64 (m, 2H); 13C NMR (CDCl3, 75 MHz) δ 21.4, 114.3, 116.7, 117.7, 124.2, 126.7 (2C), 130.8 (2C), 131.7, 133.0, 133.7, 135.9, 139.5. (2-Nitrophenyl)( phenyl)selane (Table 2, 3h).23d (245 mg, 88%), 1H NMR (CDCl3, 500 MHz) δ 7.00 (d, J = 7.5 Hz, 1H), 7.25–7.32 (m, 2H), 7.45–7.53 (m, 3H), 7.70 (d, J = 7.0 Hz, 2H), 8.30–8.32 (m, 1H); 13C NMR (CDCl3, 100 MHz) δ 125.9, 126.2, 128.3, 130.0, 130.2 (2C), 130.4, 133.7, 136.0, 137.5 (2C), 145.7. (4-Nitrophenyl)( phenyl)selane (Table 2, 3i).23d (256 mg, 92%), 1H NMR (CDCl3, 500 MHz) δ 7.33–7.38 (m, 2H), 7.50 (d, J = 8.5 Hz, 2H), 7.58–7.60 (m, 2H), 7.79 (d, J = 8.0 Hz, 2H); 13 C NMR (CDCl3, 100 MHz) δ 123.7 (2C), 128.3, 129.7, 129.8 (2C), 132.1 (2C), 134.4 (2C), 136.7, 151.5. 1-(2-(Phenylselanyl)phenyl)ethanone (Table 2, 3j).26b (206 mg, 75%), 1H NMR (CDCl3, 500 MHz) δ 2.69 (s, 3H), 6.97–6.99 (m, 1H), 7.19–7.23 (m, 2H), 7.40–7.47 (m, 3H), 7.69–7.70 (m, 2H), 7.94–7.96 (m, 1H); 13C NMR (CDCl3, 100 MHz) δ 27.3, 124.8 (2C), 129.2, 129.7, 129.8 (2C), 131.7, 132.6, 134.2, 137.5, 140.6, 198.8. 4-(Phenylselanyl)benzonitrile (Table 2, 3k).23a (237 mg, 92%), 1H NMR (CDCl3, 500 MHz) δ 7.23 (d, J = 7.5 Hz, 2H),

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7.28–7.36 (m, 5H), 7.51 (d, J = 7.0 Hz, 2H); 13C NMR (CDCl3, 125 MHz) δ 109.7, 118.8, 127.6, 129.2, 130.0 (2C), 130.3 (2C), 132.4 (2C), 135.7 (2C), 141.0. 4-(m-Tolylselanyl)benzonitrile (Table 2, 3l). Pale yellow solid (245 mg, 90%), mp 45–47 °C, 1H NMR (CDCl3, 300 MHz) δ 2.34 (s, 3H), 7.20–7.25 (m, 2H), 7.29–7.33 (m, 2H), 7.37–7.43 (m, 4H); 13C NMR (CDCl3, 75 MHz) δ 21.3, 109.6, 118.9, 127.2, 129.8, 130.1 (2C), 130.2, 132.4 (2C), 132.8, 136.3, 140.0, 141.3; IR (KBr): 3072, 2921, 2852, 2225, 1585, 1477 cm−1; anal. calcd for C14H11NSe: C 61.77, H 4.07, N 5.15; found: C 61.73, H 4.10, N 5.13%. 1-(4-( p-Tolylselanyl)phenyl)ethanone (Table 2, 3m). White solid (246 mg, 85%), mp 103–106 °C, 1H NMR (CDCl3, 500 MHz) δ 2.38 (s, 3H), 2.54 (s, 3H), 7.18 (d, J = 8.0 Hz, 2H), 7.32 (d, J = 8.5 Hz, 2H), 7.50 (d, J = 7.5 Hz, 2H), 7.76 (d, J = 8.5 Hz, 2H); 13C NMR (CDCl3, 125 MHz) δ 21.4, 26.6, 124.5, 129.0 (2C), 129.8 (2C), 130.7 (2C), 135.0, 135.8 (2C), 139.1, 141.3, 197.4; IR (KBr): 3444, 2922, 2852, 1674, 1581, 1271 cm−1; anal. calcd for C15H14OSe: C 62.29, H 4.88; found: C 62.32, H 4.83%. (4-Nitrophenyl)(m-tolyl)selane (Table 2, 3n). Yellow solid (257 mg, 88%), mp 49–51 °C, 1H NMR (CDCl3, 300 MHz) δ 2.36 (s, 3H), 7.23–7.28 (m, 2H), 7.31–7.36 (m, 2H), 7.40–7.45 (m, 2H), 7.99–8.03 (m, 2H); 13C NMR (CDCl3, 75 MHz) δ 21.4, 124.1 (2C), 127.0, 129.7 (2C), 129.9, 130.4, 136.6, 140.2, 144.3, 146.3; IR (KBr): 3053, 2921, 1573, 1508, 1340 cm−1; anal. calcd for C13H11NO2Se: C 53.44, H 3.79, N 4.79; found: C 53.47, H 3.75, N 4.81%. 2-(Phenylselanyl)benzonitrile (Table 2, 3o).23a (214 mg, 83%), 1H NMR (CDCl3, 300 MHz) δ 7.25–7.35 (m, 2H), 7.36–7.39 (m, 4H), 7.56–7.61 (m, 3H); 13C NMR (CDCl3, 75 MHz) δ 114.8, 117.5, 127.1, 128.0, 128.9, 129.8 (2C), 132.3, 133.1, 133.7, 135.2 (2C), 137.5. 4-((4-Methoxyphenyl)selanyl)benzonitrile (Table 2, 3p).23d (262 mg, 91%), 1H NMR (CDCl3, 300 MHz) δ 3.84 (s, 3H), 6.91–6.94 (m, 2H), 7.23–7.26 (m, 2H), 7.39–7.42 (m, 2H), 7.54–7.57 (m, 2H); 13C NMR (CDCl3, 75 MHz) δ 55.5, 109.2, 115.8 (2C), 117.1, 119.0, 129.2 (2C), 32.3 (2C), 138.2 (2C), 142.5, 160.8. Phenyl(4-(m-tolylselanyl)phenyl)methanone (Table 2, 3q). Pale yellow gummy mass (295 mg, 84%), 1H NMR (CDCl3, 300 MHz) δ 2.34 (s, 3H), 7.16–7.24 (m, 2H), 7.36–7.47 (m, 6H), 7.52–7.58 (m, 1H), 7.62–7.66 (m, 2H), 7.73–7.74 (m, 2H); 13 C NMR (CDCl3, 75 MHz) δ 21.4, 128.3 (2C), 128.4, 129.6 (2C), 130.0 (2C), 130.1, 130.9 (2C), 132.4, 132.5, 135.6, 135.9, 137.7, 139.8, 139.9, 196.1; IR (neat): 3055, 2921, 2852, 1655, 1581, 1278 cm−1; HRMS: m/z calcd for C20H17OSe: 353.0439 [M + H]+; found: 353.0469. Phenyl(4-( phenylselanyl)phenyl)methanone (Table 2, 3r).26c (290 mg, 86%), 1H NMR (CDCl3, 500 MHz) δ 7.35–7.42 (m, 5H), 7.45–7.51 (m, 2H), 7.56–7.67 (m, 5H), 7.71–7.78 (m, 2H); 13C NMR (CDCl3, 125 MHz) δ 128.4 (2C), 128.7 (2C), 129.8 (2C), 130.0, 130.3 (2C), 130.9 (2C), 132.5, 135.2 (2C), 135.7, 137.7, 139.6, 196.0. (4-((4-Chlorophenyl)selanyl)phenyl)( phenyl)methanone (Table 2, 3s). Pale yellow solid (290 mg, 78%), mp 114–116 °C,

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H NMR (CDCl3, 300 MHz) δ 7.30–7.39 (m, 2H), 7.40–7.61 (m, 7H), 7.66–7.72 (m, 2H), 7.75–7.78 (m, 2H); 13C NMR (CDCl3, 75 MHz) δ 127.1, 128.4 (2C), 130.0 (2C), 130.5 (2C), 131.0 (2C), 132.6, 135.1, 136.0, 136.3 (2C), 137.6, 138.7, 196.0; IR (KBr): 3064, 2923, 2852, 1649, 1583, 1471, 1276 cm−1; HRMS: m/z calcd for C19H14ClOSe: 372.9893 [M + H]+; found: 372.9890. Phenyl(4-( p-tolylselanyl)phenyl)methanone (Table 2, 3t). White solid (281 mg, 80%), mp 87–89 °C, 1H NMR (CDCl3, 300 MHz) δ 2.38 (s, 3H), 7.18 (d, J = 7.8 Hz, 2H), 7.35–7.38 (m, 2H), 7.43–7.57 (m, 5H), 7.63–7.67 (m, 2H), 7.74–7.78 (m, 2H); 13C NMR (CDCl3, 75 MHz) δ 21.4, 124.6, 128.4 (2C), 129.6 (2C), 130.0 (2C), 130.7 (2C), 130.8 (2C), 132.4, 135.4 (2C), 135.8, 137.8, 139.1, 140.5, 196.1; HRMS: m/z calcd for C20H17OSe: 353.0439 [M + H]+; found: 353.0442. (4-((4-Methoxyphenyl)selanyl)phenyl)( phenyl)methanone (Table 2, 3u). Pale yellow solid (319 mg, 87%), mp 97–100 °C, 1 H NMR (CDCl3, 300 MHz) δ 3.83 (s, 3H), 6.90–6.93 (m, 2H), 7.28–7.32 (m, 2H), 7.42–7.47 (m, 2H), 7.53–7.65 (m, 5H), 7.72–7.74 (m, 2H); 13C NMR (CDCl3, 75 MHz) δ 55.4, 115.6 (2C), 117.9, 128.3 (2C), 128.8 (2C), 129.9 (2C), 130.8 (2C), 132.3, 135.1, 137.8, 138.0 (2C), 141.4, 160.6, 196.0; IR (KBr): 3471, 3055, 2923, 2846, 1647, 1583, 1489, 1280, 1246 cm−1; HRMS: m/z calcd for C20H17O2Se: 369.0388 [M + H]+; found: 369.0387. 2-(2-(Phenylselanyl)phenyl)furan (Scheme 2, 4a). Brown gummy mass (225 mg, 75%), 1H NMR (CDCl3, 300 MHz) δ 6.52–6.54 (m, 1H), 6.84 (d, J = 3.3 Hz, 1H), 7.06–7.11 (m, 1H), 7.16–7.28 (m, 2H), 7.32–7.36 (m, 3H), 7.55–7.59 (m, 3H), 7.66–7.69 (m, 1H); 13C NMR (CDCl3, 75 MHz) δ 109.5, 111.6, 126.6, 128.3, 128.5, 129.7 (2C), 129.9, 131.1, 131.7, 132.1, 135.3 (2C), 142.3, 152.9; IR (neat): 3411, 3055, 1664, 1579, 1461, 1435 cm−1; anal. calcd for C16H12OSe: C 64.22, H 4.04; found: C 64.30, H 4.01%. 1-(4-(Phenyltellanyl)phenyl)ethanone (Scheme 3, 5a).23a (165 mg, 51%), 1H NMR (CDCl3, 300 MHz) δ 2.55 (s, 3H), 7.26–7.38 (m, 3H), 7.60–7.63 (m, 2H), 7.71–7.79 (m, 2H), 7.80–7.83 (m, 2H); 13C NMR (CDCl3, 75 MHz) δ 26.5, 113.4, 124.2, 128.8 (2C), 128.9, 129.9 (2C), 135.9, 136.0 (2C), 139.7 (2C), 197.7. (4-Nitrophenyl)( phenyl)tellane (Scheme 3, 5b).23a (176 mg, 56%), 1H NMR (CDCl3, 300 MHz) δ 7.31–7.36 (m, 2H), 7.42–7.47 (m, 1H), 7.59 (d, J = 9.0 Hz, 2H), 7.85–7.88 (m, 2H), 7.97 (d, J = 8.7 Hz, 2H); 13C NMR (CDCl3, 75 MHz) δ 112.7, 123.9 (2C), 127.9, 129.5, 130.3 (2C), 135.5 (2C), 140.4 (2C), 147.3 1

Acknowledgements We are pleased to acknowledge the financial support from DST, New Delhi through an award of JCB Fellowship to B. C. R. (Grant no. SR/S2/JCB-11/2008). BCR also thanks Indian National Science Academy, New Delhi for the offer of INSA Senior Scientist to him. P. M. thanks CSIR for his fellowship. We thank the supercomputing facility at IACS for computational support.


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