Proton magnetic resonance studies of compounds with bridgehead nitrogen. Part XXVII. Configurational and conformational studies with derivatives of perhydro-oxazolo[3,4-d][1,4]oxazine

Abstract

Replacement of the 7-methylene group in perhydro-oxazolo[3,4-a]pyridine by an oxygen atom markedly increases the proportion of cis-fused conformer in the cis ⇌trans-fused ring conformational equilibrium from ca., 30% to ca. 86%. This result is interpreted largely in terms of differences in non-bonded interactions, but changes in ring-fusion strain also appear to be important.