Photochemical [2+2] cycloaddition of cyclic enones to (5R)-5-methyloxy-2[5H]-furanone

The [2+2] Photocycloaddition of different cyclic enones to (5R)-5-menthyloxy-2[5H]-furanone is investigated. The diastereoselectivity relative to the chiral acetal centre and the regio and the eso/endo ratios of the products have been determined. By variation of the structure of cyclic enones, the diastereoselectivity could be optimised to 9/1. The results lead to the conclusion that the photochemically excited cyclopentenone transfer its energy to the (5R)-5-menthyloxy-2[5H]-furanone. The subsequent reaction of the excited furanone with cyclopentenone in its ground state is less stereoselective, as already observed. However, cyclic enones which furnish mixed adducts with (5R)-5-menthyloxy-2[5H]-furanone with high facial diastereoselectivity, react in their T-1 state. (C) 1998 Elsevier Science Ltd. All rights reserved.