A convenient and practical route to novel α-allenic ketones through a Wittig reaction

Article abstract of DOI:10.1055/s-1999-2805

A convenient synthesis of novel 5-arylpenta-3,4-diene-2-ones (3a-g) through a Wittig reaction of acetylmethylentriphenylphosphorane (2) with arylketenes is described.

Full text of DOI:10.1055/s-1999-2805

LETTER
1237
A Convenient and Practical Route to Novel a-Allenic Ketones through a Wittig
Reaction
K. Kumar, S. Kaur, M. P. S. Ishar*
Department of Pharmaceutical Sciences, Guru Nanak Dev University, Amritsar- 143 005, Punjab, India.
Fax +91-183-258819-20; E-mail: dcse_gndu@yahoo.com
Received 18 May 1999
gener-ated in situ from the corresponding acid chlorides
Abstract: A convenient synthesis of novel 5-arylpenta-3,4-diene-
(1), with acetyl-methylentriphenylphosphorane (2). Thus,
2-ones (3a-g) through a Wittig reaction of acetylmethylentriphe-
inverse addition of a solution of phosphorane (2) and tri-
nylphosphorane (2) with arylketenes is described.
ethylamine in dichloromethane to acid- chlorides (1a–g)
Key words: a-allenic ketones, Wittig reaction, phosphorane,
at -20 to 0°C, provided allenic ketones (3a–g) in high to
arylketenes
good yields (Table 1)9; a higher yield (90%) of 3c was ob-
tained when diphenylketene, generated from diphenylace-
tylchloride and triethyl- amine and distilled10, was reacted
Many natural products possessing an a-allenic ketone
with acetylmethylentriphenyl- phosphorane. The obtained
moiety display important biological properties.1 Addi-
allenic ketones have been characterized spectroscopical-
tionally allenic ketones are being increasingly involved as
ly.11 In their IR spectra, compounds 3a–g displayed, inter-
key intermediates in organic synthesis.2 A number of
alia,
a
band around 1935-1940 cm-1 which is
methods for the preparation of allenic ketones have been
described1a,2, however, the reported methods are beset
with a number of inherent difficulties and the search for
newer methods is drawing con- siderable attention.2 In
continuation of our research on allenyl carbonyl
compounds3 we were interested in developing an easy
route to variably substituted a-allenic ketones, required
for investigation of their excited state chemistry. It was
observed that, although a variety of substituted allenic es-
ters have been synthesized3,4 through a Wittig reaction of
characterisitic of allenic moiety12; the structures of 3a–g
are also corroborated by NMR spectral data, particularly,
the 13C NMR spectral assignments.12
R2
CH COCl
Et N, Dry CH Cl ,
O
R2
PPh3
-20 to 0°C
2
3
2
H
COCH3
Ph3P=CHCOCH3
2
R1
1
R1
alkoxycarbonylmethylentriphenylphosphorane
with
ketenes, the corres-ponding synthesis of a-allenic ketones
through Wittig reaction of acetylmethylentriphenylphos-
phorane with alkyl-/arylketenes has not been synthetically
exploited, in spite of the known lack of reactivity of the
latter phosphorane towards ketones5, and an earlier report
regarding reaction of acetylmethylentriphenylphospho-
rane with ketene.6 The lack of interest in this reaction was,
probably, due to a reported reaction of the phosphoranes
with allenic ketones through a nucleophilic attack at cen-
tral allenic carbon7 (Scheme 1).
- Ph3P=O
H
R2
5
4
3
1
2
CH3
O
3
R1
Scheme 2
Table 1
CH2
R'
H
CH3
H
R
R'
R
R
H
O
PPh3
O
PPh3
Ph3P=CH-R'
O
Scheme 1
Prompted by some recent reports on the application of a
variety of phosphonium salts for synthesis of allenic
systems8, we have investi-gated the synthesis of a-allenic
ketones through a Wittig reaction. Herein we report a
practical method for the synthesis of novel 5-aryl-penta-
3,4-diene-2-ones through a Wittig reaction of arylketenes,
The reaction failed in the case of alkylketenes and yields
of allenic ketones were relatively lower in cases where the
aryl groups possessed mesomerically electron-donating
Synlett 1999, No. 8, 1237–1238 ISSN 0936-5214 © Thieme Stuttgart · New York

1238
K. Kumar et al.
LETTER
(10) Diphenylketene was prepared and isolated according to proce-
dure described in Organic Synthesis, Coll. Vol. VI, p. 549.
(11) (a) Spectral data for allenic ketones:
substituents (Table 1). The present method is thus a useful
extension of the Wittig reaction to obtain novel aryl sub-
stituted allenyl methyl ketones, in good to high yield,
which have not been obtained by any other known meth-
ods.
3a: Colorless oil, IR (thin film, neat): 1935, 1682, 1601, 1358,
1231, 754, 698 cm-1; 1H NMR(CDCl3, 200 MHz): δ 2.27 (s,
3H, -CH3), 6.13 (d, 1H, J = 6.2 Hz), 6.62 (d, 1H, J = 6.2 Hz),
7.29 (m, 5H, Ar-Hs); 13C NMR(CDCl3, 50 MHz): δ
215.3(C4), 196.6 (C2), 131.8(C), 128.9 (CH), 128.4 (CH),
127.6(CH), 100.6(C5), 98.2(C3), 26.3 (C1); Mass : m/z
159(17, M++1),158 (87, M+), 102(100).
3b: Pale yellow oil, IR (thin film, neat): 1935, 1682, 1609,
1358, 1229, 756, 695 cm-1; 1H NMR(CDCl3, 200 MHz): δ
2.25 (s, 3H), 2.36 (s, 3H), 6.11 (d, 1H, J = 6.2 Hz), 6.59 (d, 1H,
J = 6.2 Hz), 7.27 (m, 4H, Ar-Hs); 13C NMR(CDCl3, 50 MHz):
δ 215.7(C4), 196.9(C2), 138.1(C), 129.7 (CH), 129.20(C),
127.21 (CH), 101.13(C5), 98.39(C3), 26.66(C1), 21.2 (CH3);
Mass:m/z 173(20, M++1), 172 (98, M+), 91(100).
3c: Viscous pale oil, IR (thin film, neat): 1934, 1680, 1606,
1356, 1221, 1121, 749, 702; 1H NMR(CDCl3, 200 MHz): δ
2.34 (s, 3H, CH3), 6.22 (s, 1H), 7.36-7.29 (m, 10H, Ar-Hs);
13C NMR(CDCl3, 50 MHz): δ 214.9(C4), 197.4 (C2),
133.8(C), 128.6(CH), 128.4(CH), 127.0(CH), 113.6 (C5),
99.8(C3), 26.7 (C1); Mass: m/z 235(16, M++1), 234(65, M+),
77(100).
3d: Off-white semisolid, IR (thin film with CHCl3): 1936,
1682 cm-1; 1H NMR(CDCl3, 200 MHz): δ 2.25 (s, 3H, -CH3),
6.11 (d, 1H, J = 6.2 Hz), 6.56 (d, 1H, J = 6.3), 7.16 (br d, 2H,
J = 8.30 Hz), 7.47(br d, 2H, J = 8.3 Hz); 13C NMR(CDCl3, 50
MHz): δ 214.7(C4), 195.7(C2), 132.0(CH), 130.6 (C),
127.8(CH), 124.6(C), 100.3(C5), 96.9 (C3), 26.1(C1) ; Mass:
m/z 238 ( 90, M++2), 236 (100, M+).
Acknowledgement
Financial support from the Department of Science & Technology,
Govt. of India, is gratefully acknowledged. The authors are thankful
to BASF, Germany, for the gift of R3-11 catalyst.
References and Notes
(1) (a) Huche, M. Tetrahedron 1980, 36, 331 and references cited
therein. (b) Robinson, C.H.; Covey, D.F. In The Chemistry of
Ketenes and Related Compounds; Patai, S., Ed.; John Wiley &
Sons: New York, 1980, Part I, pp 451-486.
(2) (a) Marshall, J.A.; Wang, X.-J. J. Org. Chem. 1991, 56, 960
and references cited therein. (b) Nagao,Y.; Lee,W.-S.; Kim,
K. Chem. Lett. 1994, 389. (c) Nagao, Y.; Lee, W.-S.; Komaki,
Y.; Sano, S. Shiro, M. Chem. Lett. 1994, 597. (d) Naham, S.;
Weinreb, S.M. Tetrahedron Lett. 1981, 22, 3815. (e) Santelli-
Rouvier, C.; Lefrere, S.; Santelli, M. J. Org. Chem. 1996, 61,
6678. (f) Reuter, J. M.; Solomon, R. G. Tetrahedron Lett.
1978, 3199. (g) Marshall, J. A.; Tang, Y. J. Org. Chem. 1993,
58, 3233. (h) Gras, J.-L.; Galledou, B.S.; Bertrand, M. Bull.
Soc. Chim. Fr. 1988, 757 and references cited therein. (i)
Hashmi, A. S. K.; Ruppert, T. L.; Knofel, T.; Bats, J. W.
J. Org. Chem. 1997, 62, 7295.
(3) (a) Ishar, M. P. S.; Wali, A.; Gandhi, R. P. J. Chem. Soc.,
Perkin Trans. I 1990, 2185. (b) Ishar, M. P. S.; Gandhi, R. P.
Tetrahedron, 1993, 49, 6729. (c) Ishar, M. P. S.; Kumar, K.
Tetrahedron Lett. 1999, 40, 175.
(4) Lang, R.W.; Hansen, H.-J. Helv. Chim. Acta 1980, 63, 438.
(5) Trippett, S. and Walker, D.M., J. Chem. Soc., 1961, 1266.
(6) Hamlet, Z.; Barker, W.D. Synthesis 1970, 543.
(7) Buono, G.; Peiffer, G.; Guillemonat, A., C. R. Acad. Sci. Paris
1970, 271C, 937.
3e: Pale yellow viscous oil, IR (thin film, neat): 1940, 1688
cm-1; 1H NMR(CDCl3, 200 MHz): δ 2.27(s, 3H, CH3), 6.14(d,
1H, J = 6.0 Hz), 6.59 (d, 2H, J = 6.0 Hz), 7.29 (br d, 2H, J =
8.4 Hz), 7.43 (br d, 2H, J = 8.5 Hz); 13C NMR(CDCl3, 50
MHz): δ 215.4(C4), 196.5(C2), 134.3(C), 129.4 (CH),
128.9(C), 128.5(CH), 101.1(C5), 97.5(C3), 26.7 (C1); Mass:
m/z 194 (3, M++2), 192(8, M+), 112(100).
3f: Pale yellow viscous oil, IR (thin film, neat): 1940, 1688
cm-1; 1H NMR(CDCl3, 200 MHz): δ 2.25(s, 3H, CH3), 3.80(s,
3H, OCH3), 6.11 (d, 1H, J = 6.2 Hz), 6.63( d, 1H, J = 6.2 Hz),
(8) (a) Nagaoka, Y.; Tomioka, K. J. Org. Chem. 1998, 63, 6428.
(b) Reynolds, K. A.; Dopico, P. G.; Brody, M. S.; Finn, M .G.
J. Org. Chem. 1997, 62, 2564. (c) Reynolds, K. A.; Finn, M.
G. J. Org. Chem. 1997, 62, 2574.
(9) General procedure for the synthesis of allenic ketones (3a-
g): To a well stirred solution of arylacetylchloride (24.0
mmol) in dry CH2Cl2 (60 mL) was added, dropwise, a solution
of triethylamine (24.0 mmol.) and
6.86( bd, 2H, J = 8.8 Hz), 7.20(d, 2H, J = 8.9 Hz); 13
C
NMR(CDCl3, 50 MHz): δ 214.1 (C4), 195.4(C2), 157.8(C),
128.7(CH), 124.6 (C),114.2(CH), 101.1(C5), 98.06(C3),
55.1(OCH3), 25.6(C1); Mass: m/z 189(5, M++1), 188(17,M+),
43(100).
3g: Colorless viscous oil; IR (thin film, neat): 1939, 1684 cm-
1; 1H NMR(CDCl3, 200 MHz): δ 2.25 & 2.24 (overlapping
doublet and a singlets, 6H, 2 X CH3), 6.03 (m, 1H, C3-H),
7.25(m, 5H, Ar-Hs); 13C NMR (CDCl3, 50 MHz): δ
214.0(C4), 197.3(C2), 133.2(C), 127.9 (CH), 127.3(CH),
126.3(CH), 104.5(C5), 98.6 (C3), 25.7(C1), 15.4(CH3) );
Mass: m/z 173(3, M++1), 172(14, M+), 105(100).
(b) All compounds gave satisfactory microanalytical data.
Runge, W. in “The Chemistry of the Allenes”; Landor, S.R.,
Ed.; Academic Press, London, 1982, vol. 3, chapter 10, pp
775-874.
acetylmethylentriphenylphos-phorane (20.0 mmol., Merck) in
dry CH2Cl2 (150 mL) at low temperature (Table 1) under
anhydrous conditions, and N2. After the addition was over, the
reaction mixture was stirred for another half an hour. Solvent
was then removed under vacuum and the residue was
extracted by shaking with chilled n-pentane (4 x 50mL). The
pentane solution was dried over anhydrous Na2SO4 and the
solvent was again removed under vacuum to give allenic
ketones as pale yellow oils (more than 85% pure by NMR)
which were purified by flash chromatography (5% diethyl
ether in light petroleum ether as eluent). For spectroscopic
characterization the samples were purified by preparative
layer chromatography.
Article Identifier:
1437-2096,E;1999,0,08,1237,1238,ftx,en;L00699ST.pdf
Synlett 1999, No. 8, 1237–1238 ISSN 0936-5214 © Thieme Stuttgart · New York