Sugar alcohols as templates for photochemical asymmetric synthesis

Efficient asymmetric induction (optical yields ranging from 22 to 85%) is accomplished through the photoaddition reactions of residues linked to sugar alcohols. Benzene solutions of dicinnamate (5,6), tetracinnamate (2,3,4), and hexacinnamate (1) derivatives of d-mannitol were irradiated through Pyrex. Each compound underwent smooth intramolecular (2π+2π) photocycloaddition to yield cyclobutanes having the truxinic acid (head-to-head) constitution. The chiral sugar alcohol derivative used to induce asymmetry was readily removed by ester exchange with methanol, and in addition to other products, optically active dimethyl δ-truxinate (8) was afforded in either dextro- or levo-rotatory form, depending on the starting material. In the course of these studies, evidence was obtained for the photoaddition of a trans- and a cis-cinnamate residue.