ORGANIC
LETTERS
2004
Vol. 6, No. 18
3047-3050
Highly Efficient Synthesis of Terminal
Alkenes from Ketones
He´le`ne Lebel,* Danielle Guay, Vale´rie Paquet, and Kim Huard
De´partement de chimie, UniVersite´ de Montre´al, P.O. Box 6128, Station Downtown,
Montre´al, Que´bec, Canada H3C 3J7
Received May 18, 2004
ABSTRACT
The rhodium(I)-catalyzed methylenation of ketones using trimethylsilyldiazomethane proceeds to give the corresponding alkenes in good
yields (60−97%). The use of an excess of 2-propanol and 1,4-dioxane as a solvent were instrumental to obtain the desired alkenes in high
yields. Superior results were achieved with the rhodium(I)-catalyzed methylenation in comparison with the standard Wittig reaction.
The synthesis of terminal alkenes from carbonyl derivatives
is a very important reaction in organic synthesis.1 The Wittig
reaction2 has been quite reliable for this transformation,
although low reactivity with hindered carbonyl derivatives
often required an excess of reagent.3 Conversely, numerous
stoichiometric gem-bimetallic reagents have been shown to
react readily with ketones, leading to the corresponding
alkene in high yields.4 The development of a process using
a catalytic amount of a transition metal complex to achieve
methylenation reaction has been recently accomplished by
our group.5 Indeed, we showed that rhodium(I) complexes
efficiently catalyzed the methylenation of a variety of
aldehydes with trimethylsilyldiazomethane in the presence
of triphenylphosphine and 2-propanol. However, the use of
this strategy with more hindered substrates, such as ketones,
has been so far limited to ketones containing an electron-
withdrawing group, such as fluorine.6 In this communication,
we wish to report our efforts that led to the development of
an efficient procedure for the synthesis of alkenes from
various ketones.
On the basis of our previous work with fluoromethyl
ketones,6 we initially postulated that substitution of methyl
ketones with other electron-withdrawing groups, such as
acetoxy and benzoxy groups, could provide the desired
alkene under our typical reaction conditions. However, allyl
acetate 1 and allyl benzoate 2 were isolated only with
moderate yields, and the formation of a silylated phospho-
nium salt derived from the ketone was also observed (Table
1, entries 1 and 3).7 We hypothesized that increasing the
amount of 2-propanol in the reaction mixture could diminish
the Lewis acid character of the silyl reagent. Indeed, the
presence of 10 equiv of 2-propanol, 1.6 equiv of trimethyl-
(1) Kelly, S. E. Alkene Synthesis. In ComprehensiVe Organic Synthesis;
Trost, B. M., Fleming, I., Eds.; Pergamon Press: Oxford, 1991; Vol. 1, p
729.
(2) (a) Wittig, G.; Geissler, G. Liebigs Ann. Chem. 1953, 580, 44-57.
(b) Wittig, G.; Scho¨llkopf, U. Chem. Ber. 1954, 87, 1318-1330.
(3) For selected examples, see: (a) Noguchi, H.; Aoyama, T.; Shioiri,
T. Tetrahedron 1995, 51, 10531-10544. (b) Mehta, G.; Islam, K. Synlett
2000, 1473-1475. (c) Kim, D.; Lee, J.; Chang, J. Y.; Kim, S. Tetrahedron
2001, 57, 1247-1252. (d) Enders, D.; Voith, M. Synlett 2002, 29-32. (e)
Bailey, W. F.; Daskapan, T.; Rampalli, S. J. Org. Chem. 2002, 68, 1334-
1338. (f) Tanaka, M.; Imai, M.; Yamamoto, Y.; Tanaka, K.; Shimowatari,
M.; Nagumo, S. J.; Kawahara, N.; Suemune, H. Org. Lett. 2003, 5, 1365-
1367. (g) Pirrung, M. C.; Liu, H. Org. Lett. 2003, 5, 1983-1985. (h) Bagal,
S. K.; Adlington, R. M.; Baldwin, J. E.; Marquez, R.; Cowley, A. Org.
Lett. 2003, 5, 3049-3052.
(4) (a) Tebbe, F. N.; Parshall, G. W.; Reddy, G. S. J. Am. Chem. Soc.
1978, 100, 3611-3613. (b) Petasis, N. A.; Bzowej, E. I. J. Am. Chem. Soc.
1990, 112, 6392-6394. See also: (c) Tour, J. M.; Bedworth, P. V.; Wu,
R. L. Tetrahedron Lett. 1989, 30, 3927-3930. (d) Hibino, J.; Okazoe, T.;
Takai, K.; Nozaki, H. Tetrahedron Lett. 1985, 26, 5579-5580. (e)
Lombardo, L. Org. Synth. 1987, 65, 81-89. (f) Takai, K.; Kakiuchi, T.;
Kataoka, Y.; Utimoto, K. J. Org. Chem. 1994, 59, 2668-2670. (g) Nysted,
L. N. U.S. Patent 3,865,848, 1975; Chem. Abstr. 1975, 83, 1406q. (h)
Matsubara, S.; Sugihara, M.; Utimoto, K. Synlett 1998, 313-315.
(5) (a) Lebel, H.; Paquet, V. J. Am. Chem. Soc. 2004, 126, 320-328.
(b) Lebel, H.; Paquet, V. Organometallics 2004, 23, 1187-1190. (c) Grasa,
G. A.; Moore, Z.; Martin, K. L.; Stevens, E. D.; Nolan, S. P.; Paquet, V.;
Lebel, H. J. Organomet. Chem. 2002, 658, 126-131. (d) Lebel, H.; Paquet,
V.; Proulx, C. Angew. Chem., Int. Ed. 2001, 40, 2887-2890.
(6) Lebel, H.; Paquet, V. Org. Lett. 2002, 4, 1671-1674.
(7) This byproduct seems the result of a nucleophilic attack of triph-
enylphosphine onto the ketone, activated with TMSX. For a similar example,
see: Lee, S. W.; Trogler, W. C. J. Org. Chem. 1990, 55, 2644-2648.
10.1021/ol049085p CCC: $27.50 © 2004 American Chemical Society
Published on Web 08/13/2004