The conformational analysis of saturated heterocycles. Part LXI. 1,2,4,5-Tetra-alkylhexahydro-1,2,4,5-tetrazines and polycyclic analogues

Abstract

Variable temperature n.m.r., together with vibrational spectroscopy and dipole moments, allow definition of conformational equilibria of substituted hexahydro-1,2,4,5-tetrazines. The tetramethyl derivative (1) exists as a rapidly interconverting mixture of monoaxial (1Z) 70% and noncentrosymmetric diaxial (1W) 30%. The tetraethyl derivative (2) exists as rapidly interconverting (2Z) 33% and (2W) 2% together with the centrosymmetric diaxial (2X) 65%. The bicyclic dimethyl derivative (5) closely resembles (1). The tricyclic unsaturated compound (4) exists as the monoaxial (4Z) 67%, the centrosymmetric diaxial (4X) 20%, and the tetraequatorial (4Y) 13%. The tricyclic saturated compound (6) exists mainly in the tetraequatorial conformer (6Y).