[2,3]-Sigmatropic rearrangement processes of allylic ylides or their equivalents can be applied to a variety of different substrates and generate products of wide interest/applicability to organic synthesis. This review describes the development and applications of stereoselective [2,3]-rearrangement reactions in which a substoichiometric amount of a catalyst is used in either the formation of the reactive intermediate or the [2,3]-rearrangement step itself.

The tetramisole-promoted catalytic enantioselective [2,3]-sigmatropic rearrangement of quaternary ammonium salts bearing a (Z)-3-fluoro-3-arylprop-2-ene group generates, after addition of benzylamine, a range of β-fluoro-β-aryl-α-aminopentenamides containing a stereogenic tertiary fluorine substituent. Cyclic and acyclic nitrogen substituents as well as various aromatic substituents are tolerated, giving the β-fluoro-β-aryl-α-aminopentenamide products in up to 76% yield, 96:4 dr, and 98:2 er.

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This review covers the enantioselective lithiation–substitution at the α‐position of nitrogen‐containing heterocycles mediated by strong organolithium bases and chiral ligands. The reactions occur by two main mechanistic pathways: asymmetric deprotonation and asymmetric substitution. For N ‐Boc heterocycles, asymmetric deprotonation is the predominant pathway, and s ‐BuLi, in combination with chiral diamines, such as (–)‐sparteine and the (+)‐sparteine surrogate, are used. This approach is highly successful with N ‐Boc pyrrolidines, piperidines, and piperazines. Substrates for asymmetric‐substitution‐mediated reactions include some N ‐Boc heterocycles, but other N ‐substituents, such as N ‐alkyl groups, N ‐alkyl‐BY 3 salts (Y = H, F) and N ‐thioamide groups are also used. With both mechanistic pathways, the lithiated heterocycle can be transmetalated to form an organocopper or organozinc species to widen the scope of the electrophile. The full scope and limitations of this approach to synthesize enantioenriched α‐substituted aziridines, azetidines, pyrrolidines, piperidines, piperazines, azepanes and other five‐/six‐membered‐ring heterocyles are summarized.

Abstract:The cinchona alkaloid-catalysed enantioselective formal [4+2] cycloaddition of ethyl 2,3-butadienoate with a range of 1,1,1-trifluoro-and 4,4,4-trifluorobutenones is investigated for the preparation of stereodefined 6-and 4-trifluoromethyl-