Synthesis of haginin E, equol, daidzein, and formononetin from resorcinol via an isoflavene intermediate

New syntheses of haginin E, equol, daidzein, and formononetin are described in this Letter. Through a sequence of a Wittig reaction, O-alkylation, and another Wittig reaction, 4-benzyloxysalicylaldehyde, which was prepared from resorcinol in two steps, was converted into the desired diene in one pot. Subsequently, the prepared diene was subjected to ring-closing metathesis using Grubbs’ catalyst (II) to construct the desired isoflavene intermediate. Using the prepared isoflavene, certain isoflavonoids such as haginin E, equol, daidzein, formononetin, and other related compounds were derived smoothly and in good overall yields.