Carbanions lithium carbenoid reactions

Thus, magnesium carbenoid 38, generated from 1-chloroalkyl phenyl sulfoxide (37) in THF at —65°C with 2.8 eq of i-PrMgCl, reacts with a-sulfonyl lithium carbanion to lead to 1,2-di- and 1,1,2-trisubstituted olefins (60). Yields are better in such conditions as compared to the reaction described in equation 14. 

The electrophilic reaction of magnesium alkylidene carbenoids with other nucleophiles than the original Grignard reagent can also be carried out. For example, treatment of magnesium alkylidene carbenoid 157, derived from 147, with a-sulfonyl lithium carbanion afforded allenes 159 in moderated yields (equation 39/. ... 

Hammerschmidt, F. Hanninger, A. Enantioselective deproto nation of benzyl phosphates by homochiral lithium amide bases. Configurational stability of benzyl carbanions with a dialkoxyphosphoryloxy substituent and their rearrangement to optically active a-hydroxy phosphonates. Chem. Ber. 1995, 328, 823-830. Avolio, S. Malan, C. Marek, I. Knochel, P. Preparation and reactions of functionalized magnesium carbenoids. Synlett 1999, 1820-1822. 

The review by Siegel [2] covers most of the halocarbenoid chemistry. The procedures in this chapter exemplify the methods and techniques used in the generation of lithium halocarbenoids and in their subsequent functionalization reactions in accordance with the scope of this volume, only carbenoids in which the carbanionic centre is spMike ( C(Li)Hal) are considered. 

A one-carbcMi ring enlargement approach for the synthesis of 8-lactones has been developed by Satoh and Kurihara [123] (Scheme 76). Reaction of the lithium carbanion of chloromethyl phenyl sulfoxide with lactone 336 afforded a diastereo-meric mixture of the hemiacetal 337. Treatment of this adduct with three equivalents of KH in THF generated potassium enolate 338, which on addition of four equivalents of t-BuLi underwent an alkylidene carbenoid rearrangement to give alkynolate 339. Protonation of 339 by the addition of sulfuric acid facilitated the formation of m-hydroxy ketene 340, which underwent an intramolecular cyclization to afford 8-lactone 341. 

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