P number of multi-bridged annulenes have so far been synthesized, especially by Vogel. 1). However, the monomethano-bridged annulenes over 18-.
Tetrahedron Letters,Vo1.27,No.22,pp Printed in Great Britain
2467-2470,1986
0040-4039/86 $3.00 + .OO Pergamon Journals Ltd.
THE SYNTHESIS OF METHANO-BRIDGED BISDEHYDR0[18]-, -[20]-, -[22]-, AND -[24]ANNLJLENES JGro Ojima,*a Emiko Ejiri,a Tadahito Kato,a Shigeyasu Kuroda, and Mitsuo Shibutani b aDept.
Faculty
of Chemistry,
930, Japan and
b
Dept.
Toyama University, Summary:
of Science,
of Industrial
Gofuku,
Toyama
Toyama
Chemistry,
University, Faculty
b
Shuji Hirooka,
b
Gofuku, Toyama
of Engineering,
930, Japan
Title annulenes were synthesized by Wittig reaction of cyclohepta-
1,3,5-triene-1,6-dialdehyde or its vinylogous dialdehydes with 3-methylpenten2-yn-4-yltriphenylphosphonium bromide, followed by intramolecular oxidative couplings of the resulting acyclic compounds, and they proved to be diatropic or paratropic, corresponding to the number of peripheral n-electrons. P number of multi-bridged annulenes have so far been synthesized, especially by Vogel. 1) However, the monomethano-bridged annulenes over 18membered ring have few precedents, ') although the mono;ythano-bridged aza[l7]and [Zllannulenes have been synthesized by Sondheimer.
We now describe a simple, and apparently general, new synthesis of dehydroannulenes which formally have a methano-bridge between 1 and 6 sites on the annulene perimeters. The method has been used for the synthesis of methano-bisdehydro[l8]-, -[221-, and -[24]annulenes. The starting material was cycloheptatriene-1,6-dialdehyde
-[20]-,
(&I,),which was
converted to mono- ;tk [lemon yellow, mp 76-77°C)4) or bis-vinylogue ,I_%') by Wittig condensation with controlled quantities of [(1,3-dioxolan-2-yl)methyl]triphenylphosphonium bromide, 6) and LiOMe or LiOEt in DMF at 75'C, followed by hydrolysis with dilute HCl in THF at room temperature. Then the homologation for ,@ was repeated, giving rise to the bis-vinylogue && (dark yellow, mp 95-
la: m=n=O
3a: m=n=O
4a:m=n=O
b: m=l,n=O
b: m=l,n=O
c: m=n=l
c: m=n=l
b: m=l,n=O c:m=n=l
d: m=2,n=l
d: m=2,n=l
d: m=2,n=l
2467
2468 96°C).
The yields of these condensations from lower homologues were 50-90%.
Reaction of ,&-$ and the salt S7) in THF with BuLi at -70°C afforded the acyclic compounds 22-g in 5-40% yields ($8: red, mp 91-92'C, 'H NMR in CDC13 at 200 MHz T 2.85-3.72 (olefinic and 7-membered ring H), 6.48 (-C-CH), 7.15 (-CH2-), 8.05 (CH3); 3,b,: red, mp 97-98OC, t 2.85-3.73 (olefinic and 7-membered H), 6.35, 6.63 (-C-CH), 7.24 (-CH2-), 8.04 (CH3); ,& (red, mp 116-117'C, T 3.14-3.70 (olefinic and 7-membered H), 6.55 (-CECH), 7.28 (-CH2-), 8.05 (CH3); ,3$: red, mp 95-96'C, 'I 3.08-3.90 (olefinic and 7-membered H), 6.64, 6.66 (-C=CH), 7.29 (-CH2-), 7.99, 8.04 (CH3). Oxidative couplings of ,&-,Q with anhydrous copper(I1) acetate in pyridina-ether
(3:l) under relatively dilute
conditions8) afforded the desired bisdehydroannulenes $2-4 as stable crystals with metallic lustre ($8 [18]-: brown, mp 169-170°C, 'H NMR in CDC13 at 200 MHz t 1.95 (d, J=15 Hz, HA), 2.18 (d, 10, H'), 2.56 (broad s, H1, H2), 7.47 (s, CH3), 7.97 (dd, 15, 10, HB), 10.45 (s, -CH2-), and see Fig. 1; ,4k [20]-: purple, mp 131-132'C, T 0.25 (dd, 16, 10, HD'), 0.35 (dd, 16, 11, HB), 2.20 (dd, 16, 9, HB'), 2.71 (d, 16, HA'), 3.94 (dd, 16, 9, H"),
4.01-4.11 (m, H2, H3), 4.06 (d, 10,
HE'), 4.16-4.22 (m, H1, H4), 4.27 (d, 10, H'), 4.41 (d, 16, HA), 5.36 (s, -CH2-), 8.44 (s, CH3), and see Fig. 1; ,4x [22]-: brown, mp 196-197'C (dec), T 2.50 (d, 16, HA), 2.51 (d, 11, HE), 2.54 (dd, 16, 11, H'), 2.81-2.85 (m, H2), 2.97-3.01 (m, H1), 6.14 (dd, 16, 11, HD), 6.22 (dd, 16, 11, HB), 7.64 (s, CH3), 9.19 (s, -CH2-), and see Fig. 1; $2 [24]-: purple, mp 195-196'C, t 0.76 (dd, 15, 11, HF'), 1.14 (dd, 15, 11, HD), 1.32 (dd, 15, 11, HB), 1.43 (dd, 15, 10, HB'), 1.55 (dd, 15, 11, HD'), 3.86-3.90 (m, H2, H3), 3.94 (d, 11, HG'), 4.06 (d, 16, HA') (dd, 16, 10, H"),
4.09 'A 4.15-4.20 (m, H1, H4) , 4.17 (d, 10, HE), 4.21 (d, 15, H ),
4.26 (dd, 15, 11, HE'), 4.29 (dd, 15, 11, Hc) , 5.88 (s, -CH2-), 8.36 (s, CH3), 8.39 (s, CH3), and see Fig. 1; these assignments of ft$were clarified by examination of two-dimensional spectrum taken at 360 MHz. Comparison of the 'H NMR chemical shifts of the various protons of the bisdehydro[l8]- and -[22]annulenes $2 and ,4~ with those of the corresponding acyclic model compounds 2~ and 2% indicates that both 3% and $I; are diatropic, as expected of peripheral 18~r- and 22Ir-electron systems, respectively. This follows from the fact that all the outer protons including methyl protons in V?J 4a and $a resonate at lower field than the corresponding protons in $2 and &, respectively, whereas the inner protons including methylene protons in $
and
4c resonate at higher field. On the other hand, S'L 4b and $2 are paratropic, as 'L'li expected of ZOIT- and 24n-electron systems, respectively, since the inner protons including methylene protons in $Q and t,d resonate at lower field than the corresponding protons in ,33 and S&
respectively, whereas the outer protons
including methyl protons resonate at higher field. The 'H NMR spectra of the bisdehydroannulenes 4.~4% are illustrated in Fig. 1, which shows that the diatropic or the paratropic nature in $e-$ can be deduced without having to make comparisons with the corresponding acyclic models 3a-d, respectively. As we see from Fig. 1, although the appearance of the sharp SL'L ?J A' B' singlet due to inner methylene protons in the spectra of $$-?I, and the H , H
2469
TM5
H2O
TMS
z
AN
’
2
6
7
10
9
6
:H2CHCl3 /$(
-CH3
t#+
tfl-i%%”
Ld
CHCl3 I
1
proton
signals
4a, $z-,d, %% chemical the
of
require shift
chemical off
in
,Q
> $&. one
decrease
of
flexibility have
us
further
the
of
an unexpected
the
become the
a methano-bridge
less
methylene
as
and as
along
the
the
explain, inner
on the
perimeter.
ring
perimeter,
in
ring albeit
9
CDC13 the
comparison that
the
current
spectra of
of
the
protons
or
of
diatropicity
falls
diamagnetic
increases,
an increase
bisdehydroannulene
with
paratropicity the
8
in
and outer
indicates
paramagnetic size
,Q-$
compared
to
protons
ring
with
of
olefinic
$4 > 4c, while the 11% behaviour that both
system
tropicity of
the
region, the
’ /I 6
5
NMR spectra
investigation between
sequence
Thus,
4
The 200 MHz ‘I!
in
[4n+Z]n-electron
electron
1.
$k
shifts
falls in
3
differences
order
L
2 Fig.
W
ring
off
in
the
current
effect
in
effect [4n]n-
seems to reflect both a size 2) and an increasing the
annulenes
4a-d
2470
In electronic spectra, taken in THF, of the annulenes, the main maximum of the'[l8]annulene $e (343 nm) is in longer wavelength than that of the [20]annulene ,Q (324 nm), and the similar observation is made between the [22]annulene $6 (367 nm) and the [24]annulene $6 (3.55nm). Clearly, this is due to the occurrence of the same sort of alternation between the maxima of [4n-21 and [4n]systems, as has been observed for monocyclic annulenes and dehydroannulenes [(4n-2)n systems absorbing at higher wavelengths than the (4n)T Systems]. 9) In addition, it is noteworthy that these annulenes $%-$ are thermally stable (vide ante) when compared with the corresponding membered, monocyclic, annulenes and dehydroannulenes, 10) presumably due to rigidity of the ring skeleton by methylene bridge. Further progress on methano-bridged annulenes are now in progress. We thank Prof. E. Vogel, University of Kaln, for providing the experimental details of preparing cyclohepta-1,3,5-trien-1,6_dialdehyde,
and Hofmann-La
Roche, Basel, for a gift of cis-3-methylpent-2-en-4-yn-l-01. References 1) For a review, see E. Vogel, Pure AppZ.
Chem.,
54, 1015 (1982).
2) A. Sablijie and N. Trinajstie, J. Org. Chem., 46, 3457 (1981). 3) P. J. Beeby and F. Sondheimer, Angew.
Gem.,
84,
896
(1972); ibid., 85, 404
(1973). 4) All new compounds described in this paper gave IR, 'H NMR, and mass spectral data consistent with the assigned structures and satisfactory elemental analyses were obtained. 5) K. Yamamoto, M. Shibutani, S. Kuroda, E. Ejiri, and J. Ojima, Tetrahedron Lett.,
in press.
6) T. M. Cresp, M. V. Sargent, and P. Vogel, J. Chem. Sot., Perkin Trrans. I, 1974,
37.
7) 0. Isler, L. H. Chopard-did-Jean, M. Montavon, R. Riiegg, and P. Zeller, HeZv.
Chim.
Acta.,
40,
1256 (1957).
8) N. Darby, T. M. Cresp, and F. Sondheimer, J. Org. Chem., 42, 1960 (1977). 9) P. J. Garratt and K. Grohmann, Houben-Weyl, Methoden der Organischen Chemie, Georg Thieme Verlag, Stuttgart, 1972, vol. V, part Id, p. 533. 10) For reviews, see (a) F. Sondheimer, Ace. Chem. Res., 2, 81 (1972); (b) M. Nakagawa, Pure Appl.
Chem.,
44, 885
(Received in Japan 25 February 1986)
(1975).
