ON THE STEREOSELECTIVITY OF NITRONE ADDITION TO ALPHA-DIPHENYLPHOSPHINOYLALKENES

The title reaction was investigated for both achiral and alpha-chiral alkenes 1-3, and for cyclic and acyclic nitrones 4 and 8. In each case , addition to allyldiphenyl phosphine oxide 1 gave a single isoxazolid ine 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 alpha-chiral alpha-di phenylphosphinoyl 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 archiral cases, and also by analogy with the addition of nitrile oxides to the same alkenes. In o ne case (6a) this was confirmed by chemical conversion. This conversio n also demonstrated the potential of this method for the synthesis of 2-(alk-2'-enyl)piperidines, e.g. 17, having defined double-bond geomet ry.