DBU-catalyzed annulation strategy for modular assembly of 2,3-difunctionalized dihydrobenzofurans

An organocatalytic approach for the construction of 2,3-dihydrobenzofuran scaffold through a formal [4 + 1] annulation of 2-(2-nitrovinyl)phenols and α-bromoacetophenones in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) has been developed. This protocol could be easily performed in one mmol scale, giving a broad range of 2,3-dihydrobenzofuran derivatives in moderate to excellent yields and remarkable diastereoselectivity (>20 : 1 dr in general) with good functional group tolerance.