1,3-DIPOLAR CYCLOADDITION OF NITRONES AND NITRILE OXIDES TO 5,5-DIMETHYL-3-METHYLENEPYRROLIDINE-2-THIONE

A simple synthesis of title compound (3) and a number of different cycloadditions are described. C-Aroyl- and C,N-diphenyl-nitrones react regio- and stereoselectively to the C=C exocyclic double bond of 3, to give only spirocycloadduct (10). On the other hand, C-phenyl-N-methylnitrone gives a mixture of diastereomeric spirocycloadducts (10) and (11). Nitrile oxides undergo 1,3-dipolar cycloaddition both to the exocyclic C=C and C=S double bonds with subsequent cycloreversion and formation of spiro-lactams (6). The appropriate spiro-thiolactams (8) were synthetized by treatment of 6 with Lawesson's reagent.