Synthesis of N-Bridgehead Fused Bicyclic b-Lactams through Organo- metal-mediated Transformations of 1,2-Dialkenylaziridines

Abstract

N-Bridgehead fused bicyclic β-lactams have been synthesized through sequential organometal-mediated transformations of 1,2-dialkenylaziridines, namely Co 2 (CO) 8 -catalysed carbonylation and ring-closing metathesis (RCM). When firstly subjected to RCM conditions, either with Schrock-Hoveyda or Grubbs' catalyst, 1,2-dialkenylaziridines did not afford the expected bicyclic N-bridgehead products. In contrast, however, cis-1,2-dialkenylaziridines were amenable to carbonylative ring expansion, affording trans-1,4-dialkenyl-β-lactams which could be subsequently metathesized to the corresponding fused bicyclic compounds using Grubbs' catalyst. Unexpectedly, carbonylation of trans-1,2-dialkenylaziridines occurred with the unprecedented rearrangement to the 5,6-dihydro-4H-[1,3]oxazine skeleton.