BETA-LACTAM AND GAMMA-LACTAM BY NICKEL POWDER MEDIATED 4-EXO OR 5-ENDO RADICAL CYCLIZATIONS - A CONCISE CONSTRUCTION OF THE MESEMBRINE SKELETON

N-Alkenyl trichloroacetamides, upon treatment with nickel powder and a cetic acid in refluxing 2-propanol undergo reversible 4-exo radical cy clisation. The cyclised radical can be trapped in different ways leadi ng to B-lactams. When the trap is omitted or not efficient enough, unu sual irreversible 5-endo cyclisation occurs affording functionalised f ive-membered lactams. Synthesis of bicyclic gamma-lactams has also bee n examined providing in few steps an access to the Sceletium alkaloids skeleton. (C) 1998 Elsevier Science Ltd. All rights reserved.