New polycyclic 2-azetidinones having fused or not biaryl units are easily prepared by the tin-mediated, intramolecular aryl-aryl radical cyclization of readily available arylsubstituted 2-azetidinones. The regioselectivity and efficiency of the process is determined both by the length of the linking chain through the beta-lactam nucleus and by the number and position of the substituents on the aromatic acceptor ring. (C) 1998 Elsevier Science Ltd. All rights reserved.