Proton magnetic resonance studies of compounds with bridgehead nitrogen. Part 34. Stereochemistry of 8,9,10,11,11a,11b,12,13-octahydro-7aH-quino[1,2-c][1,3]benzoxazines and 7a,8,9,10,10a,10b,11,12-octahydrocyclopent[5,6][1,3]oxazino[3,4-a]quinolines

Abstract

Four diastereoisomeric 8,9.10,11,11a,11b.12,13-octahydro-7aH-quino[1,2-c][1,3]benzoxazines and two 7a.8,9,10,10a,10b.11,12-octahydrocyclopent[5,6][1,3]oxazino[3,4-a]quinolines have been synthesised and their configurations assigned by ¹H n.m.r. spectroscopy. In the case of the quinobenzoxazines the r-7a,c-11a,c-11b compound adopts the trans-BC conformation, the r-7a,t-11a,c-11b- and the r-7a,c-11a,t-11b-compounds both exist predominantly in the trans-Bc conformations, and the r-7a,t-11a,t-11b-compound predominantly adopts the cis-BC-O-outside conformation. Similar conformational preferences are exhibited by the r-7a,c-l0a,c-10b- and the r-7a,t-10a,c-10b-cyclopenta-analogues. 4,4a,5,6 -Tetrahydro-3H-[1,3]oxazino[3,4-a]quinoline and its 3methyl derivatives all adopt predominantly the trans-fused ring conformations in solution at room temperature.