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