Recent Developments in the [1,2]‐Wittig Rearrangement

Abstract

The stereochemical features and synthetic potentials of the [1,2]‐Wittig rearrangement are reviewed.

[1,2]- and [1,4]-Wittig rearrangements of α-alkoxysilanes: effect of substitutions at both the migrating benzylic carbon and the terminal sp2 carbon of the allyl moiety

“…The isomerizations of ethers under basic conditions to the corresponding alcohols are known as Wittig rearrangements and can proceed via two main pathways: A stepwise [1,2]-migration involving a radical/radical-anion species 1 or via a concerted symmetry-allowed [2,3]-shift. 2 In addition, during the reorganization of allylic ethers [1,4]-Wittig rearrangements can compete with the [1,2]-migration and give rise to carbonyl compounds.…”

“…1 In cases of limited radical stability of the migrating group, carbanion-stabilizing groups similarly facilitate [1,2]-migrations. 1 In contrast, the yield of [1,4]-Wittig products has been reported to be relatively insensitive to substitution at the α- or γ-position of the allylic moiety, 3 although Schlosser observed that [1,4]-/[1,2]-selectivity is diminished with increasing alkyl substitution about the migrating carbon.…”

“…1 In cases of limited radical stability of the migrating group, carbanion-stabilizing groups similarly facilitate [1,2]-migrations. 1 In contrast, the yield of [1,4]-Wittig products has been reported to be relatively insensitive to substitution at the α- or γ-position of the allylic moiety, 3 although Schlosser observed that [1,4]-/[1,2]-selectivity is diminished with increasing alkyl substitution about the migrating carbon. 8 In the context of these previous findings, we set out to systematically investigate the introduction of alkyl substitution at the benzylic carbon and/or terminal allylic carbon of α-alkoxysilanes so as to gain insight into the steric and stereochemical factors that might control the course of Wittig rearrangements of α-alkoxysilanes.…”

Development of Ar‐BINMOL‐Derived Atropisomeric Ligands with Matched Axial and sp3 Central Chirality for Catalytic Asymmetric Transformations

“…Despite the fact that the Wittig rearrangement is a synthetically useful tool in organic chemistry for the construction of secondary alcohols, the synthetic utilization of the [1,2]‐Wittig rearrangement remains severely limited because of rather low yields and the restricted range of substrates in most cases . Inspired by previous examples of the diastereoselective [1,2]‐Wittig rearrangement, we have successfully developed a facile and practical methodology for the stereoselective construction of the secondary alcohol moiety as well as the highly efficient synthesis of enantiomerically pure BINOL‐derived diols, the aforementioned Ar‐BINMOLs, with axial and sp 3 central chirality through the [1,2]‐Wittig‐rearrangement‐based axial‐to‐central chirality transfer or diastereoselective induction . In this diastereoselective Wittig rearrangement (Scheme ), the stereoselective process exhibited a perfect level of diastereoselectivity, good substrate scope, and excellent yields, thus allowing access to a broad range of chiral Ar‐BINMOLs.…”

The Alkylation of Carbanions

“…This happens frequently when highly enolized aldehydes or ketones (e.g. [1,2]-Wittig (X = O) [190][191][192], Stevens (X = NR 2 + ) [193][194][195], or related rearrangements [195,196]) or a-elimination to yield carbenes (Scheme 5.20). In these circumstances transmetalation (e.g.…”