Phosphoryl-stabilized carbanions

Maryanoff, B.E. and Reitz, A.B. (1989) The Wittig olefination reaction and modifications involving phosphoryl-stabilized carbanions. Stereochemistry, mechanism, and selected synthetic aspects. Chemical Reviews, 89(4), 863-927. 

A convenient route to trivinylphosphine has been developed by thiol elimination from tris[2-(phenylthio)ethyl]phosphine oxide.56 The reaction mechanism involves a phosphoryl-stabilized carbanion, from which benzene thiolate anion is eliminated. 

HWE olefination Stereoselective olefination of aldehydes and ketones using phosphoryl-stabilized carbanions. 212... 

Arlamkina, G.A., Sazonov, P.K., and Beletskaya, I.P., Arylation of phosphoryl-stabilized carbanions with metal Jt-complexes of aryl chlorides and fluorides, Tetrahedron Lett., 42, 4385, 2001. 

Y 22. Maryanoff. B.E. Reitz, A.B. The Wittig Olefination Reaction and Modifications Involving Phosphoryl-Stabilized Carbanions. Stereochemistry, Mechanism, and Selected Synthetic Aspects Chem Rev. 1989, 89, 863-927... 

The Wittig Olefination Reaction and Modifications Involving Phosphoryl-Stabilized Carbanions. Stereochemistry, Mechanism and Selected Synthetic Aspects"... 

The disadvantages of the Wittig reaction described in Section A led to the development of modified olefination methods based on phosphoryl-stabilized carbanions. The most important modification of the Wittig reaction in the field of carotenoid synthesis is olefination by means of phosphonate carbanions, as introduced by Homer [55] and by Wadsworth and Emmons [56]. 

Vedejs, E. Peterson, M. J. The Wittig Reaction Stereoselectivity and a History of Mechanistic Ideas (1953-1995) Advances in Carbanion Chemistry, 1996, 2, 1-85. Vedejs, E. Peterson, M. J. Stereochemistry and Mechanism in the Wittig Reaction Topics in Stereochemistry 1994,21,1-157. Maryanoff, B. E. Reitz, A. B. The Wittig Olefmation Reaction and Modifications Involving Phosphoryl-Stabilized Carbanions. Stereochemistry, Mechanism, and Selected Synthetic Aspects Chemical Reviews 1989, 89, 863-927. 

The mechanism for the HWE reaction is shown in above for an aldehyde condensation. The phosphoryl-stabilized carbanion 15 attacks the carbonyl in a stepwise manner, to give oxyanion intermediate 16, which then decomposes via a transient four-centered intermediate, 17A or 17B, to yield... 

By far the main interest in the reaction of halo [ C] acetates with phosphorus nucleophiles is for the preparation of phosphoryl-stabilized carbanions for use in Wittig and related reactions. The presence of the additional electron-withdrawing ester group provides additional stabilization, significantly modifying the reactivity of the ylide species and the stereochemical course of its reactions. The two phosphorus reagents discussed here include the triphenylphosphonium salt type 158. precursors of Wittig methylenetriphe-nylphosphoranes, and the trialkylphosphonoacetate type 159. applied in the Horner-Wadsworth-Emmons family of reactions . ... 

As was presented above, the nature of the interaction between the carbon center and the metal(s) for groups 1-3 and actinides has been probed by DFT calculations. Because of the energies of the orbitals involved, it can be expected that the orbital overlap, and thus the covalency of the M=C bond, would be better with group 4 metals. Muller et al. have focused on the rotation barrier about the P-C bond in the mixed Ti/Li silyl-phosphonate system (see Scheme 30) in order to compare it to the barrier found in phosphoryl-stabilized carbanions. They obtained a very similar barrier of rotation, meaning that the presence of the Ti center did not enhance the configurational stability at the C center [95]. 

In these a-phosphorylated dithioesters, the electron-withdrawing effect of the phosphono group, which strongly increases the electrophilic character of the thiocarbonyl group, makes the latter more prone to the thiophilic attack of nucleophiles and stabilizes the resulting carbanion. The main reactions of 1 with nucleophiles are summarized in Scheme 2. 

Not only alky] groups, but also aryl [492, 493], vinyl [494], acyl [276, 495—497], alkoxycarbonyl [498], aminocarbonyl [499-501], silyl [502-504], or phosphoryl groups [279, 280] can migrate to a vicinal carbanion (Scheme 5.68). Because some of these groups can be used to stabilize a-heteroatom-substituted carbanions by chelate formation, migration of these groups to the carbanion is a potential side reaction in the generation and alkylation of chelate-stabilized carbanions. 

The ready alkylation of sodium phosphonate carbanions with chloro- or bromoacetates in THF provides a useful access to dialkyl 2-(alkoxycarbonyl)ethylphosphonates bearing a variety of alkyl, aryl, cyano, keto, or phosphoryl groups at the cx-carbon (Scheme 8.43). By using a chiral auxiliary, the alkylation of phosphorus-stabilized benzylic carbanions with bromoacetate proceeds with high diastereoselectivity to provide an easy access to optically active alkylphosphonic acids. ... 

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