The Azomethine Ylid Strategy in β-Lactam Synthesis. Application to Selenapenams

Using azomethine ylid reactivity available from the β-lactam-based oxazolidinone 1, selenoketones 6a–e react as 1,3-dipolarophiles to give racemic selenapenams 7a–e in a single step. The cycloaddition sequence proceeds with complete control of regiochemistry and the thermodynamically more stable C(3)/C(5) relationship is observed. The selenothiocarboxylate 9a and the selenocarboxylate 9b also function as effective dipolarophiles, but attempts to convert the resulting cycloadducts 10a and 10b to the corresponding selenapenems were unsuccessful. Other selenium-containing dipolarophiles failed to give characterizable cycloadducts.