The stereochemistry and reactions of some 3,4-disubstituted chromans

Abstract

Hydrolysis of trans-3,4-dihalogenochromans yielded trans-3-halogeno-4-hydroxychromans; borohydride reduction of 3-halogenochroman-4-ones gave cis-3-halogeno-4-hydroxychromans. The ¹H n.m.r. coupling constants of these compounds showed that the hetero-ring exists in the half-chair conformation, with both substituents axial in the trans-isomer, and that the most stable conformation of the cis-isomer is that in which the 4-substituent is pseudo-axial.