WITTIG REARRANGEMENT OF AROMATIC ACETALS AND KETALS INDUCED BY REDUCTIVE ELECTRON-TRANSFER

The [1,2]-Wittig rearrangement, i.e., the migration of groups from oxygen to carbon in benzyl and related ethers promoted by alkyl- or aryllithium derivatives to afford alkoxides, is well known. Much effort has been devoted to the study of both its mechanistic aspects1and synthetic usefulness.2 It is generally accepted1-7 that the reaction proceeds through the formation of an intermediate benzylic carbanion, which subsequently rearranges via a noncon-certed radical cleavage-recombination mechanism (Scheme I). This view is supported by the migratory aptitude of substituents R (allyl ≃ benzyl > methyl > ethyl > phenyl), which parallels the order of free radical stabilities,8,9and by the fact that optically active precursors usually lead to partial racemization.1,10Far less studied is the related rearrangement of aromatic acetals or ketals promoted by electron transfer from alkali metals. To the best of our knowledge, nothing further has appeared in the literature since the early report of Schlenk and Bergmann11on. © 1990, American Chemical Society. All rights reserved.