Kinetic control Wittig olefination

As mentioned above (see Scheme 1), three main directions of the decomposition of intermediates that formed are possible when phosphorus and arsenic ylides react with compounds bearing C=X bonds 5,6,19,63,64,88 (i) elimination of R3E15=X to form olefins (Wittig type reaction) (ii) retro-Wittig type decomposition and (iii) elimination of R3E15 and formation of three-membered cycles (Corey-Chaykovsky type reaction). According to the data of Erker and coworkers,12,13,51 under kinetic control, the reaction of phosphorus ylides with thiocarbonyl compounds also affords phosphines and thiiranes, whose further transformations lead to olefins and R3PS under thermodynamic control. 

The Wittig reaction is a very important method for olefin formation. The stereochemistry about the new carbon-carbon double bond is the Z (or less stable) isomer. This unusual stereoselectivity indicates that product formation is dominated by kinetic control during formation of the oxaphosphetane. 

The reaction which uses the phosphorus ylide also produces31 35,77 highly stereo-selectively 1 -heterosubstituted-1 -vinylcyclopropanes, but now the (Z)stereoisomers are the major ones (Schemes 61, 62 a, 63 a). It is well-known that in the Wittig reaction the betaines which lead to the (Z)-disubstituted olefins are formed under kinetically controlled conditions and that any feature which favours the elimination of triphenyl-phosphine oxide from these betaines should increase the amount of the (Z)stereoiso-... 

Piers and Morton have reported that lithium (phenylthio)(trimethyl-stannyOcuprate smoothly transfers one trimethylstannyl group to a,/3-acetylenic esters in a conjugate sense to give /3-trimethylstannyl-a,/3-olefinic esters. Importantly, products of almost exclusive E- or Z-geometry are formed under conditions of kinetic or thermodynamic control. Partial reduction followed by Wittig... 

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