A new preparative route to substituted dibenzofurans by benzannulation reaction. An application to the synthesis of cannabifuran

A new regioselective pathway to substituted dibenzofuran derivatives is described here. According to this procedure substituted 1-acetoxy-3-alkoxycarbonyl dibenzofurans are obtained by treatment of 6-(2-methoxyaryl)-3-alkoxycarbonylhex-3-en-5-ynoic acids with acetic anhydride in the presence of sodium acetate. The latter acids are prepared from the easily available substituted o-iodo-anisoles by Sonogashira coupling with propargylic alcohol and Wittig reaction as the key steps. The described benzannulation reaction proceeds in regioselective fashion and a range of substituents are tolerated. Its synthetic utility is demonstrated by a new synthesis of cannabifuran, a naturally occurring dibenzofuran.