Cyclopropanation with isopropylidenetriphenylphosphorane

Two developments in the syntheses involving addition of a Me2C group (with isopropylidenetriphenylphosphorane, Vol. 4, p. 486, Ref. 242) to fumaric acid derivatives have been published, with the idea of synthesizing chiral compounds. De Vos and Krief (whose names were originally attached to the route ) have used the dimenthyl ester 258, and obtained 74% diastereoisomeric excess (optically pure after one crystallization) of the traru-substituted cyclopropane... 

Miscellaneous Reactions of Methylenephosphoranes.—The synthesis of three-membered rings by means of phosphorus ylides has been reviewed and there have been several new reports of this type of reaction. Optically active a,p-un-saturated esters have been converted into cyclopropanes highly stereoselectively by reaction with isopropylidenetriphenylphosphorane as the key step in syntheses of both (li ,3 )-chrysanthemic acid methyl ester (53) and the (IR) cis-gem dibromovinyl analogue (54). The addition of reactive phosphonium ylides to functionalized 1,3-butadienylphosphonates provides a new synthesis of 2-cyclopen ten-1 -ylphosphonates (5 5). ... 

Cyclopropanation of 24 with isopropylidenetriphenylphosphorane and subsequent isolation of the predominant isomer provides 27, which is oxidatively converted to aldehyde 28, the substrate required for preparation of the biologically active insecticide ( S)-bioallethrin (29) [19,20] (Scheme 7). 

The Diels-Alder reaction of 694 with cyclopentadiene is a relatively slow process that proceeds to give in 90% the single product 705, where only one outside face undergoes the cycloaddition reaction. Cyclopropanation of 694 with isopropylidenetriphenylphosphorane does not take place, presumably due to steric crowding [212]. 

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