Thermal rearrangements of cyclic amine ylides. V. Thermolysis of 6-ethynyl-1-methyl-1,2,5,6-tetrahydropyridine N-imides and N-ylides.

Abstract

The thermolysis of the N-imides (14, 15) of 6-ethynyl-1-methyl-1, 2, 5, 6-tetrahydropyridines (11) resulted in [2, 3]-sigmatropic rearrangement with either the triple bond or the double bond in the ring to give the dihydro-1, 2-diazonines (16) presumably via the allenic intermediates (19) and the tetrahydropyrazoles (17, 18). On the other hand, the N-ylides (26) of 11 gave the allenic compounds (27) and the Hofmann elimination products (28). Heating the N-oxides of 11 resulted in decomposition to give no characterizable products. The mechanisms, including stereochemistry, of these thermal reactions are discussed.