STEREOSELECTIVITY AND SPINSELECTIVITY OF PRIMARY (SINGLET) AND SECONDARY (TRIPLET) NORRISH TYPE-II REACTIONS

The influence of reactive conformation and substitution pattern on the Norrish Type II reactivity and selectivity of singlet-excited phthali mides was investigated. Only the cis-diasteroisomer of the 4-tert.-but yl cyclohexylamine derivatives 1 underwent Yang cyclization. The phtha loyl leucine esters 3a and 3b both gave primarily Yang cyclization wit h subsequent ring expansion. As a secondary photoreaction, 3a gave Nor rish II cleavage solely, wheras photolysis of the tert.-butyl ester 3b resulted in a 1:1 mixture of Norrish II cleavage and Yang cyclization product 4 and 5. (C) 1998 Elsevier Science Ltd. All rights reserved.