|
|
|
|
M. Hatanaka, Y. Himeda, and I. Ueda
[J. Chem. Soc. Perkin Trans., Vol.1, p.2269, 1993]
A convenient method for the synthesis of substituted cyclopentadienes has been developed using allylidene(triphenyl)phosphoranes. (3-Ethokycarbonyl-2-substituted-2-propenylidene)triphenylphosphoranes 1 reacted with α-halogenoketones 2 under very mild reaction conditions to undergo a [3+2]-annulation leading to the regioselective formation of tri- or tetra-substituted cyclopentadienes 3 in good to excellent yields. Allylidenephosphoranes 1 also reacted with S-ethyl bromoethanethioate to yield 4-ethylthiocyclopentadienes, which was readily converted into a cyclopentenone.
