Micellar Control of Organic Reactions: Propellane Substrates as Stereochemical Probes for Micellar Binding

Propellanediones and their reduction products have been used to demonstrate that micellar binding can control reaction diastereoselectivity. Borohydride reduction of the propellane carbonyl in an aqueous solution of a cationic surfactant provides clear evidence for this new kind of micellar perturbation of organic reactions. In addition to the expected rate enhancement that cationic micelles provide for the borohydride reduction, they direct the approach of the borohydride to one face of the reduction substrate. The source of this effect and its scope are explored. A correlation of micellar capabilities with substrate shape is presented. An explanation of these results is suggested. It is based on a particular model for the geometry of substrate-micelle binding and on micelle-directed attack of the prebound reagent.