Synthesis and ring-chain tautomerism of angularly substituted cycloalkane-fused tetrahydro-1,3-oxazines

Starting from 1-methyl-1-cyclopentene and -cyclohexene, regioisomeric 1,3-amino alcohols 6a,b and 7a,b were prepared by regio-and stereospecific reactions. When the amino alcohols were condensed with aromatic aldehydes, well-defined products 8-11 were obtained, which exist as three-component tautomeric mixtures in CDCl3 solution. When equation (1) was applied in all four sets 8-11, good linear correlations were obtained. For regioisomeric compounds, introduction of the methyl group in the bridgehead position resulted in reverse effects on the stability. (C) 1997 Published by Elsevier Science Ltd. All rights reserved.