Free-radical annelation in the synthesis of bicyclic β-lactams. 2. Alternative use of chloro-, phenylseleno-, and phenylthio-functionalities as free-radical precursors
Free radical annulation in the synthesis of bicyclic .beta.-lactams. 4. Exo vs. endo cyclizations in the construction of the (.+-.)-1-oxacepham and (.+-.)-1-oxahomocepham systems