Sulfoxides, vinyl Michael-type

Vinylic sulfoxides have been used successfully in several Michael-type asymmetric syntheses. 

Allyl vinyl ethers have also been obtained by elimination reactions, e.g., intramolecular bromo-etherification/base-catalyzed hydrogen bromide elimination164 166( 0r the phenylseleno etherifi-cation/selenoxide elimination reaction158 167. Tertiary allylic alcohols have been vinylated by a Michael-type addition to a vinyl sulfoxide followed by elimination of benzenesulfenic acid168. 

There are numerous reports of the P-addition of organometallic reagents to racemic a,p-unsaturated sulfoxides [62,63]. For example, the Michael-type reaction of dialkylcuprates with p-chlorophenyl vinyl sulfoxide (65), followed by reaction of the initially formed a-sulfinyl carbanion (66) with electrophiles such as benzophenone, gave the products (67) (Scheme 5.21) [66]. 

Tertiary allylic alcohols can be vinylated by a Michael-type addition to a vinyl sulfoxide 4, followed by eUmination of PhSOH (Eq. 3.1.6) [11]. A solution of the sulfoxide 5 was heated in the presence of both sodium bicarbonate and a-pinene, which is utihzed to scavenge released sulfinic acid and minimizing unwanted side reactions, to give the bicycUc alcohol 6 in 45% yield. 

An intramolecular version of enolate Michael addition to enantiomerically pure vinylic sulfoxides is represented by reaction of a cyclopentenone sulfoxide with dichloroketene (Scheme 5)90 this type of additive Pummerer rearrangement has been developed by Marino and coworkers91 into a highly effective way of constructing variously substituted lactones in very high enantiomeric purity (equation 43). 

Michael-Additions The most important application of this type of reaction is the carbon-carbon bond formation p to a carbonyl function by the addition of carbanion. The asymmetric version of the Michael-addition has been known since 1973. An optically active vinyl sulfoxide served as chiral auxiliary198). 

Pummerer Reaction. The reagent transforms sulfoxides in the presence of catalytic amounts of zinc iodide into the corresponding a-silyloxy sulfides (eq 1). Vinyl sulfoxides undergo a Michael-Pummerer type reaction to give y-silyloxy-y-phenylthio esters (eq 2). ... 

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