2,3-Wittig Rearrangement
The ,3Wittig rearrangement is the transformation of an allylic ether into a homoallylic alcohol via a concerted, pericyclic process. Because the reaction is concerted, it exhibits a high degree of stereocontrol, and can be employed early in a synthetic route to establish stereochemistry. The Wittig rearrangement requires strongly basic conditions, however, as a carbanion intermediate is essential. ,2Wittig rearrangement is a competitive process. Introduction ,3Sigmatropic rearrangements occur for a variety of groups X and Y (see below). When X is a carbanion and Y an alkoxide, the rearrangement is called the ,3Wittig rearrangement and the products are pent-1-en-5-ols. The ,2Wittig rearrangement, which produces isomeric pent-5-en-1-ols, is a competitive process that takes place at high temperatures. Because of the high atom economy and stereoselectivity of the ,3rearrangement, it has gained considerable synthetic utility. The carbanion is generated by direct lithiation of m ...
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Allylic
In organic chemistry, an allyl group is a substituent with the structural formula , where R is the rest of the molecule. It consists of a methylene bridge () attached to a vinyl group (). The name is derived from the scientific name for garlic, . In 1844, Theodor Wertheim isolated an allyl derivative from garlic oil and named it "". The term allyl applies to many compounds related to , some of which are of practical or of everyday importance, for example, allyl chloride. Allylation is any chemical reaction