The use of ionic chiral sensitizers in the crystalline state: application to the di-pi-methane photorearrangement of a benzonorbornadiene derivative

Simultaneous asymmetric induction and triplet-triplet energy transfer has been achieved in the di-pi-methane photorearrangement of a benzonorbornadiene derivative through the use of ’ionic chiral sensitizers’. In this approach, salts formed between a reactant carboxylic acid and optically pure sensitizer amines are irradiated and the products monitored for optical activity following removal of the ionic auxiliary. In contrast to the results in solution, where only racemic products are formed, photolysis of the salts in the crystalline state leads to enantiomeric excesses as high as 91% at 100% conversion. (C) 1999 Elsevier Science Ltd. All rights reserved.