Syntheses oftrans-Isoflavan-4-ols

The reaction of nitrous acid and three 4-aminoisoflavan hydrochlorides (III, IV, and V) obtained by the catalytic hydrogenation of isoflavanone oximes, and the hydroboration of three isoflavenes (XII, XIII, and VIII), were investigated in the hope of finding a general method of synthesizing trans-isoflavan-4-ols. The reaction of III and IV with nitrous acid afforded the corresponding trans-4-ols, though in a poor yield, but that of V produced no expected compound, the corresponding isoflavene (VIII) being obtained instead. The hydroboration of XII, XIII, and VIII afforded the corresponding trans alcohols (VI, VII, and XIV) in good yields. In addition, it became clear that 4-aminoisoflavans obtained by the catalytic reduction of the oximino compounds possess the 3,4-cis configuration.