Proton magnetic resonance studies on compounds with bridgehead nitrogen. Part XXXI. Reversible dimerisation of perhydropyrido [1,2-c][1,3]oxazepines; X-ray analysis of a fourteen-membered macrocyclic dimer; conformational analysis of perhydropyrido [1,2-c][1,3]oxazepines

Abstract

Perhydropyrido(1,2-c)[1,3] oxazepine, cis(9-H, 5a-H)-9-methyl-, trans(8-H, 5a-H)-8-ethyl- and 8-methyl-, and cis(7-H, 5a-H)-7-methylperhydropyrido[1,2-c][1,3]oxazepine (6a, h, d, f, and c) undergo an unusual dimerisation from the liquid state; X-ray analysis shows that the crystalline dimer of the 8-ethyl compound contains a 14-membered heterocyclic ring. Epimers of the 8-ethyl and 8-methyl compounds together with cis(6-H, 5a-H)-6-methylperhydropyrido[1,2-c][1,3]oxazepine do not undergo the dimerisation and exist in solution predominantly in the cis-fused ring conformation. Compounds (6c, d, f, and h) prefer the trans-fused ring conformation.