The enamine route to 2-morpholinoisoflav-3-ene

Abstract

In contrast to earlier reports, the condensation of N-styrylmorpholine with salicylaldehyde or with 3-methoxysalicylaldehyde gives 2-morpholinoisoflav-3-ene derivatives. 2-Morpholinoisoflav-3-ene can be hydrogenolysed in a useful synthesis of isoflavan; with acids it gives in high yield a remarkably stable di(isoflavenyl) ether (6); with triphenylmethyl perchlorate it gives isoflavylium perchlorate.

A similar condensation with N-(cyclohexenyl)morpholine behaves differently, giving alcohols that are oxidised to chromone (or tetrahydroxanthone) derivatives, in accord with previous reports.