The azomethine ylid strategy in beta-lactam synthesis. Application to selenapenams

Using azomethine ylid reactivity available from the beta-lactam-based oxazo lidinone 1, selenoketones 6a-e react as 1,3-dipolarophiles to give racemic selenapenams 7a-e in a single step. The cycloaddition sequence proceeds wit h complete control of regiochemistry and the thermodynamically more stable C(3)/C(5) relationship is observed. The selenothiocarboxylate 9a and the se lenocarboxylate 9b also function as effective dipolarophiles, but attempts to convert the resulting cycloadducts 10a and 10b to the corresponding sele napenems were unsuccessful. Other selenium-containing dipolarophiles failed to give characterizable cycloadducts. (C) 2000 Elsevier Science Ltd. All r ights reserved.