Reaction of a wide variety of aldehydes with the easily prepared 2-azadienes, in the presence of BF3 etherate, furnishes the corresponding hetero Diels-Alder adducts which have been converted, mainly, to cis epoxides via N-Boc protection followed by one-pot two-step ring opening and nucleophilic displacement of the halogen atom, resulting in final formation of an oxirane ling. (C) 2004 Elsevier Ltd. All rights reserved.