N-ALKENYL NITRONE DIPOLAR CYCLOADDITION ROUTES TO PIPERIDINES AND INDOLIZIDINES .7. HYDROXYLAMINE ALKYNE CYCLIZATIONS - FORMATION OF CYCLICNITRONES AND APPLICATION TO THE SYNTHESIS OF THE PROPOSED STRUCTURE FOR (+ -)-ACACIALACTAM/

The cyclisation of the alkynylhydroxylamines 2, 13, 14, 19, 27, 34, 39 , 46 and 47 to give five-, six- and seven-membered cyclic nitrones is described. A concerted intramolecular ene-like pathway is proposed for the addition of the N-O-H group across the triple bond. Using the nit rone 48 as the starting material, the seven-membered lactam structure 49 proposed for the natural product acacialactam was prepared and was found to be incorrect.