On the stereoselectivity of nitrone addition to α-diphenylphosphinoylalkenes

Abstract

The title reaction was investigated for both achiral and α-chiral alkenes 1–3, and for cyclic and acyclic nitrones 4 and 8. In each case, addition to allyldiphenylphosphine oxide 1 gave a single isoxazolidine product. The configurations of these isoxazolidines (5 and 9) were investigated by NMR methods, and found to be consistent with reaction via exo transition states. Nitrone additions to α-chiral α-diphenylphosphinoyl alkenes 2 and 3 gave two diastereoisomeric products in all cases studied. The configurations of these isoxazolidines (6, 7, 10, 11) were assigned by analogy with the achiral cases, and also by analogy with the addition of nitrite oxides to the same alkenes. In one case (6a) this was confirmed by chemical conversion. This conversion also demonstrated the potential of this method for the synthesis of 2-(alk-2′-enyl)piperidines, e.g. 17, having defined double-bond geometry.