Electron-deficient olefins phase-transfer catalysis

The catalytic asymmetric epoxidation of electron-deficient olefins, particularly a,P-unsaturated ketones, has been the subject of numerous investigations, and as a result a number of useful methodologies have been elaborated [44], Among these, the method utilizing chiral phase-transfer catalysis occupies a unique position in terms of its practical advantages. Moreover, it also allows the highly enantioselective epoxidation of trans-a,P-unsaturated ketones, particularly chalcone. 

The first organocatalytic asymmetric aziridination reactions of electron-deficient olefins made use of either (i) a chiral tertiary amine combined with a 0-phosphinyl or sulfonyl hydroxylamine for the in situ generation of aminimides as aziridination reagents [133, 134], or (ii) a quaternary salt of cinchona alkaloids in phase-transfer catalysis in combination with ethyl nosyloxycarbamate [135], A-acyl A-aryl... 

Enantioselective oxidation is one of the most important and yet useful transformations in organic synthesis, and the asymmetric phase-transfer catalysis has made notable contributions to this field. The stereoselective epoxidation of electron-deficient olefins with peroxides is a representative example, and Taylor demonstrated the synthetic utility of this system by accomplishing the total syntheses of three natural products of manumycin family, (-l-)-MT 35214 131, (-l-)-manumycin A 132, " and (—)-alisamycin 133 (Scheme 4.31). The syntheses were undertaken by the... 

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