1676 Bull. Chem. Soc. Jpn., 76, No. 8 (2003)
Ó 2003 The Chemical Society of Japan
chromatographed over silica gel by elution from hexane and di-
chloromethane to give 4-chlorostyrene (4c) (114 mg, 0.82 mmol)
and triphenylphosphine oxide (253 mg, 0.91 mmol). 1H NMR
(CDCl3) ꢀ 5.17 (d, 1H, J ¼ 11 Hz, =CH2), 5.62 (d, 1H, J ¼ 17
Hz, =CH2), 6.56 (dd, 1H, J ¼ 11 and 17 Hz, =CH), 7.16–7.26
(m, 4H, Ar). 13C NMR (CDCl3) ꢀ 114.64 (=CH2), 127.63,
128.87, 133.64, 135.88 (=CH), 136.25.
Other reactions were carried out in a similar manner.
Reaction of Benzyltriphenylphosphonium Bromide (2b)
with DBU Followed by the Addition of Benzaldehyde. To a
refluxing solution of 2b (520 mg, 1.2 mmol) in dichloromethane
(10 mL) was added DBU (230 mg, 1.5 mmol). After refluxing
for 30 min, 3a (106 mg, 1.0 mmol) in dichloromethane (3 mL)
was added to this solution. After refluxing for 2 h, the reaction
mixture was washed with water (5 mL ꢁ 3), dried over magnesi-
um sulfate, filtered, and evaporated to afford a pale-yellow oil,
which was chromatographed over silica gel by elution from hex-
ane and dichloromethane to give stilbene 4f (167 mg, 0.93 mmol,
E=Z ¼ 56=44) and triphenylphosphine oxide (250 mg, 0.90
mmol). The mixture of stilbene was recrystallized from ethanol
Scheme 2.
methyltriphenylphosphonium bromide with DBN resulted in
the formation of methoxycarbonylmethylenetriphenylphos-
phorane, which further reacted with benzaldehyde to afford
methyl cinnamate in 76% yield. However, this ylide is well
known as an isolable stabilized ylide. They did not apply
the formation of normal unstabilized ylides. Recently,
Imamoto et al. reported on the synthesis of indoles by an intra-
molecular Wittig reaction by using triethylamine and DBU as
bases.6 The present result is the first example on the formation
of normal unstabilized or semistabilized ylides by using ami-
dine derivatives. Nishizawa et al. reported the indirect synthe-
sis of olefins via the isolation of 1,2-hydroxyphosphonium
salts and subsequent treatment with DBU,9 whereas the present
method does not require the isolation of 1,2-hydroxyphospho-
nium salts.
10
ꢂ
to giꢂve colorless crystals of trans-4f. mp 121–123 C (lit. mp
124 C).
Other reactions were carried out in a similar manner.
10
ꢂ
ꢂ
trans-4-Methylstilbene (4g): mp 116–118 C (lit. mp 119 C).
trans-4-Nitrostilbene (4h): mp 153–155 ꢂC (lit.10 mp 155 ꢂC).
1H NMR (CDCl3) ꢀ 7.13 (d, 2H, J ¼ 16 Hz, =CH), 7.26 (d,
2H, J ¼ 16 Hz, =CH), 7.26–7.57 (m, 5H, Ph), 7.62 (br d, 2H, J ¼
7 Hz, Ar), 8.22 (br d, 2H, J ¼ 7 Hz, Ar). 13C NMR (CDCl3) ꢀ
124.34, 126.48, 127.05, 127.22, 129.04, 129.09, 133.51, 136.37,
144.05, 146.97.
References
1
For a review, see: E. J. Coyne and D. G. Gilheany, ‘‘Com-
In conclusion, we have shown that the Wittig reaction by us-
ing DBU as a base in dichloromethane gave olefins in good
yields.
prehensive Organic Functional Group Transformations,’’ ed by A.
R. Katrinsky, O. Meth-Cohn, and C. W. Rees, Pergamon, Oxford
(1995), Vol. 3, Chapter 3.13, pp. 491–499.
2
For reviews, see ‘‘Reagents for Organic Synthesis,’’ ed by
Experimental
L. S. Fieser and M. Fieser, John Wiley & Sons, New York (1967–
2000), Vol. 1–20.
3
Lett., 1974, 2587; G. Markl and A. Merz, Synthesis, 1973, 295.
General. Flash chromatography was carried out by Merck
Kieselgel 60 (230–400 mesh). Thin layer chromatography
(TLC) was carried out on commercially available pre-coated alu-
minum plates (Merck silica Kieselgel 60F254). All solvents were
distilled before use, and no further treatment was carried out.
NMR spectra were measured on a JEOL GSX-400 (400 MHz
W. Tagaki, I. Inoue,Y. Yano, and T. Okonogi, Tetrahedron
¨
M. A. Baanchette, W. Choy, J. T. Davis, A. P. Essenfeld,
4
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5
Ber., 99, 2012 (1966).
6
2885 (2002).
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1
Materials. Phosphonium salts 2a, b and benzaldehydes 3a–e
were purchased from Wako. Styrenes 4a–e and stilbenes 4f were
identified from authentic samples obtained from Aldrich (4a, 4b,
and 4e) and TCI (4c, 4d, and 4f).
S. Taira, H. Danjo, and T. Imamoto, Tetrahedron Lett., 43,
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K. Okuma, Y. Sato, and H. Ohta, J. Org. Chem., 59, 2390
Reaction of Methyltriphenylphosphonium Bromide 2a with
DBU Followed by the Addition of 4-Chlorobenzaldehyde (3c).
To a refluxing solution of 2a (714 mg, 2 mmol) in dichlorometh-
ane (10 mL) was added DBU (339 mg, 2.2 mmol). After refluxing
for 30 min, 3c (141 mg, 1.0 mmol) in dichloromethane (3 mL) was
added to this solution. After refluxing for 5 h, the reaction mixture
was washed with water (5 mL ꢁ 3), dried over magnesium sulfate,
filtered, and evaporated to afford a pale-yellow oil, which was
(1994); K. Okuma, Y. Sato, H. Ohta, and Y. Yokomori, Bull.
Chem. Soc. Jpn., 67, 1855 (1994).
8
(1987).
9
R. Schwesinger, Angew. Chem., Int. Ed. Engl., 26, 1164
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