Thermal rearrangements of cyclic amine ylides. IV. Rearrangement of .BETA.,.GAMMA.-unsaturated 1-alkylpiperidine N-oxides: Formation of 1,2-oxazepine derivatives.

Abstract

The thermolysis of 1-methyl-2-vinylpiperidine N-oxide (13) resulted in Meisenheimer [1, 2] rearrangement to give the hexahydro-1, 2-oxazepine (23) and no [2, 3]-sigmatropic rearrangement product (24). Similarly, the 1-methyl-1, 2, 5, 6-tetrahydropyridine N-oxides (15), on heating, gave only the tetrahydro-1, 2-oxazepines (26, 27), together with the Hofmann-type elimination products (28). The thermolysis of 1-benzyl-2-phenyl-(20a) and 1-benzyl-2-vinyl-piperidine N-oxide (20b) afforded the corresponding 1-benzyloxypiperidines (32) as well as the 1, 2-oxazepines (31). These results are different from those observed for open-chain allylamine N-oxides and 1-alkyl-2-vinylpiperidine N-imides and N-ylides, which are known to undergo only [2, 3]-sigmatropic rearrangement.