Photo-assisted kinetic resolution of diastereomeric limonene and carvomenthene oxides in methanol in the presence of Lewis acids

Photosolvolysis of diastereomeric R-(+)-limonene oxide and R-(+) carvomenthene oxides in methanol, in the presence of Lewis acid catalysts viz. ZnCl2, ZnBr2 and InCl3 affords resolution of (+)-trans-limonene oxide and (+)-trans-carvomenthene oxide in excellent yield. Also, the photosolvolyzed products (1S, 2S, 4R) trans-1-methoxy-2-hydroxy-p-menthane and (1S, 2S, 4R)-trans-1-methoxy-2-hydroxy-p-menth-8-ene, could be obtained in good purity. The key factor determining the selectivity in solvolysis is the presence of isopropenyl or isopropyl group on the C-4 of limonene or carvomenthene oxides.