The [2,3]‐Wittig Rearrangement

Abstract

The [2,3]‐sigmatropic rearrangement, constitutes a versatile type of bond reorganization which encompasses a number of variations in terms of an atom pair (X, Y) and the type of electron pair on Y (anions, nonbonding electron pairs, or ylides). The Sommelet–Hauser rearrangement is representative. This chapter focuses on the special class of [2,3]‐sigmatropic rearrangement that involves an oxycarbanion (X = oxygen, Y = carbanion) as the migrating terminus. This type of rearrangement is now termed the [2,3]‐Wittig (sigmatropic) rearrangement. The reaction name clearly originates from the fact that this rearrangement formally represents a [2,3]‐sigmatropic version of the classic Wittig rearrangement, a well‐known 1,2‐alkyl shift of oxycarbanions. The [2,3]‐Wittig rearrangement has a rather recent history. Perhaps the first observation of the [2,3]‐Wittig shift is the rearrangement of the allyl fluorenyl ether, which was made in 1960 in the context of mechanistic studies on the Wittig rearrangement. The period of the 1960s to the early 1970s witnessed slow progress with a focus on mechanistic studies mainly of allyl benzyl ether systems. The synthetic power of this carbanion rearrangement as a general method was recognized when Still (1978) and Nakai (1981) established the highly stereoselective variants of the genuine [2,3]‐Wittig rearrangement. In recent years the [2,3]‐Wittig rearrangement has enjoyed widespread application in many facets of organic synthesis. Various aspects of the reaction have been reviewed. This chapter deals with the mechanism, scope and limitation, stereochemistry, and synthetic applications of the [2,3]‐Wittig rearrangement with emphasis on the stereochemical aspects and the synthetic utility. Other hetero [2,3]‐Wittig rearrangements such as thio‐[2,3]‐Wittig variants are not covered.

Investigations of the [2,3]-Sigmatropic Rearrangements of Vinylaziridines and Allylic Amines

“…The reaction has received much attention from both synthetic and computational chemists, and its potential has been demonstrated in several natural product syntheses. [1][2][3] With this in mind, it was somewhat surprising to realize that the corresponding aza- [2,3]-Wittig rearrangement (Scheme 1, X = NR 2 ) had received considerably less attention at the outset of this investigation. Only a few attempts had been documented, indicating that these systems tend to be unreactive or are prone to undergo competitive [1,2]-rearrangement.…”

[1,3]‐Transfer of Chirality during the Nicholas Reaction in γ‐Benzyloxy Propargylic Alcohols

“…[4] In this regard, the [2,3]-Wittig rearrangement of ethers has also come under close scrutiny as a carbon-carbon bond-forming reaction of potential application to the stereodirected synthesis of acyclic alcohols. [5] Chirality transfer during [2,3]-sila-Wittig rearrangements allows the stereoselective formation of SiÀC bonds. [6] In the literature, very efficient chirality transfers in acyclic systems have also been achieved from chiral heteroatoms to carbon derivatives, [7] and in chiral metal complexes, [8] palladium(0)-promoted intra-and intermolecular allylation reactions, [9] and [3,3]-sigmatropic rearrangements of allylic acetates catalyzed by palladium(ii).…”

A General Strategy for the Synthesis of P‐Stereogenic Compounds

“…Thus, the present work also provides a general route to Pstereogenic H-phosphinates that is much simpler and cheaper than the desymmetrization of alkyl phosphinates. [9] An example of the exploitation of the CH 2 OH moiety is the Wittig rearrangement [10] (Scheme 5). Allylation of 3 gives Scheme 2.…”