Enantiofacially Selective Binding of Prochiral Olefins to a Chiral Catalyst via Simultaneous Face-Face and Edge-Face Aromatic Interactions

摘要

Small-molecule chiral catalysts are capable of effecting reactions with enzyme-like enantioselectivity, without sacrificing the substrate generality associated with simple synthetic reagents. Synthetic catalysts and enzymes both exert stereoin-ductionthrough molecular recognition events, yet the former are usually analyzed in terms of steric destabilization of the pathway leading to the minor enantiomeric product, while the latter are thought to operate by transition state stabilization in the pathway leading to the major enantiomer. In reality, the basis for selectivity in reactions of these catalysts may not be so different, as several examples of effective synthetic chiral catalysts have been uncovered wherein attractive, noncovalent secondary interactions between substrate and catalyst are suggested or strongly indicated by experiment. The incorporation of enzyme-like recognition elements into simple catalysts is clearly an appealing design feature, since attractive interactions can, in principle, reduce conformational degrees of freedom and enhance chiral discrimination in selectivity-determining transition states.