Diels-alder reactions with ethyl 1-benzofuran-3-carboxylates

Substituted salicylaldehydes reacted with ethyl diazoacetate to give ethyl 1-benzofuran-3-carboxylates containing various substituents in the aromatic ring. The Diels-Alder reaction of these compounds with Danishefsky’s diene was regioselective, and it provided an effective method for the construction of the heterocyclic skeleton of hexahydrodibenzo[b,d]furan-7-one or tetrahydrodibenzo[b,d]furan-7-one. The adducts were found to undergo rearrangement to substituted 4′-hydroxybiphenyl-2-yl methyl carbonates during column chromatography on silica gel.