The Wittig reaction and its variants produce no sp
3 stereocenter, nevertheless asymmetric transformation from achiral carbonyl compounds can be achieved by using optically active phosphorus reagents. These approaches are based on three different methodologies, kinetic resolution and discrimination of either π-face of carbonyl or enantiotopic carbonyl groups in the symmetrical molecules. A variety of phosphorus reagents has been reported and used for these transformations. Among the Horner-Wadsworth-Emmons (HWE) type reagents, those possessing 8-phenylmenthyl or binaphthyl groups as a chiral auxiliary exert high level of asymmetric induction. For example, the HWE reagent of binaphthyl group effectively discriminated the carbonyl face giving dissymmetric olefins, and differentiated enantiotopic carbonyls of
meso-α-diketones to afford the
Z- and
E-olefins with high optical yield. This discrimination was successfully applied to the practical one-pot procedure for optically active allenic compounds as well as the construction of the fused ring systems through the intramolecular HWE reaction.
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