ASYMMETRIC INDUCTION IN THE SOLID-STATE PHOTOCHEMISTRY OF AMMONIUM-SALTS

A general approach to using crystal chirality in asymmetric synthesis is described. An example consists of the preparation of crystalline salts of dimethyl 9-amino-9,10-ethenoanthracene-11,12-dicarboxylate (1) with optically active sulfonic acids. Photolysis of the salts in the solid state generates a product that has chiral centers in the amine-containing portion of the molecule (di-pi-methane photorearrangement). The optical activity in the photoproduct was determined by polarimetry and NMR chiral shift reagent analysis, which revealed enantiomeric excesses ranging from 30 to 68% depending on the optically active sulfonic acid employed. In contrast to the results in the crystalline state, irradiation of the salts in acetonitrile gave racemic photoproduct.