Regioselective, cascade [3+2] annulation of β-naphthols (resorcinols) with Z-enoate propargylic alcohols: a novel entry for the synthesis of complex naphtho(benzo)furans

An acid promoted, unprecedented cascade [3+2] annulation strategy for the synthesis of complex naphtho-and benzofurans is reported. An alkoxyfuranylallene intermediate (generated from Z-enoate propargylic alcohols via a Meyer-Schuster rearrangement) was employed as the 1,2-bis-electrophile and b-naphthols ( phenols) as 1,3-bisnucleophiles. This strategy represents the first cascade and metal free process for the synthesis of naphthofurans and benzofurans from propargylic alcohols. A very broad substrate scope was observed. The synthesized naphtho-and benzofuranswere efficiently transformed into the frameworks of the bioactive natural products amycofuran and frondosin B.