Allylic heteroatom-stabilized

The intramolecular 4 + 3-, 3 + 3-, 4 + 2-, and 3 + 2-cycloaddition reactions of cyclic and acyclic allylic cations have been reviewed, together with methods for their generation by thermal and photochemical routes.109 The synthetic uses of cycloaddition reactions of oxyallyl cations, generated from polybromo and some other substrates, have also been summarized seven-membered rings result from 4 + 3-cycloadditions of these with dienes.110 The use of heteroatom-stabilized allylic cations in 4 + 3-cycloaddition reactions is also the subject of a new experimental study.111 The one-bond nucleophilicities (N values) of some monomethyl- and dimethyl-substituted buta-1,3-dienes have been estimated from the kinetics of their reactions with benzhydryl cations to form allylic species.112 Calculations on allyl cations have been used in a comparison of empirical force field and ab initio calculational methods.113... 

Heteroatom-Stabilized Allylic Anions i, LiNEij MeCOsH... 

Heteroatom-stabilized Carbanions. Heteroatom-stabilized and allylic carbanions serve as homoenolate anions and acyl anion equivalents, e.g. a-anions of protected cyanohydrins of aldehydes and Q ,/3-unsaturated aldehydes are intermediates in general syntheses of ketones and Q ,/3-unsaturated ketones (eq 36). Allylic anions of cyanohydrin ethers may be a-alkylated (eq 37) or, if warmed to —25°C, may undergo 1,3-silyl migration to cyanoenolates which may be trapped with TMSCl. Metalated Q -aminonitriles of aldehydes are used for the synthesis of ketones and enamines (eq 38). Similarly, allylic anions from 2-morpholino-3-alkenenitriles undergo predominantly a-C-alkyl-ation to give, after hydrolysis, a,/3-unsaturated ketones (eq 39). ... 

The regioselectivity of the reactions of heteroatom-stabilized allylic anions with electrophiles has been thoroughly reviewed. An unsymmetrically substituted allyl anion is an ambident anion, which can react with electrophiles at two sites. The discussion of site selectivity is a major objective of this article. 

The regioselectivity of the reactions of heteroatom-stabilized allyl anions with electrophiles and carbanion stabilization by adjacent sulfur (wifh particular reference to intrinsic rate constants for proton transfer) have been reviewed. 

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