Highly Efficient and Stereoselective N-Vinylation of Oxiranecarboxamides and Unprecedented 8-endo-Epoxy-arene Cyclization: Expedient and Biomimetic Synthesis of Some Clausena Alkaloids

Catalyzed by CuI/N,N-dimethylglycine, oxiranecarboxamides underwent a highly efficient and stereoselective N-vinylation reaction with (Z)-1-aryl-2-bromoethenes to afford the corresponding enamides. The method has been applied to a straightforward synthesis of (−)-(2R,3S)-SB204900, the enantiomer of the natural product. Following a hypothetic biomimetic pathway, both (+)-(5R,6S)-ξ-Clausenamide and (−)-(5R,6S)-balasubramide have been efficiently synthesized for the first time through the unprecedented intramolecular 8-endo-epoxy-arene cyclization of (Z)-N-(phenylvinyl)oxiranecarboxamides.