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36.12.9.1.3.3 Variation 3: [1,2]-Wittig Rearrangements

DOI: 10.1055/sos-SD-036-00789

Morey, J. V.; Wheatley, A. E. H.Science of Synthesis, (2008361132.

A particularly valuable synthetic tool provided to the chemist by the Wittig rearrangement lies in the potential for utilizing the stereocontrol implicit in the process. This has led to the frequent employment of such rearrangements over a number of years in stereoselective syntheses and the following discussion reflects this emphasis. It stands to reason that the determination of stereochemistry may occur either during or after formation of the metal alcoholate. That is, stereospecific rearrangement of either of the two configurationally stable carbanionic enantiomers formed may follow enantiotopic deprotonation of a prochiral reagent either by a chiral base or in the presence of an external chiral ligand (ECL). Alternatively, interconversion of metalated enantiomers may yield an enantiomeric excess. This might be achieved thermodynamically, though fast interconversion in a system where stereoisomers exhibit significantly different propensities for rearrangement yields kinetically resolved products.

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