Highly regioselective synthesis of 2,3-disubstituted 2H-1-benzopyrans: Brønsted acid catalyzed [4+2] cycloaddition reaction with a variety of arylalkynes via ortho-quinone methides

A highly regioselective one-pot synthesis of 2,3-disubstituted-2H-1-benzopyrans has been developed through Brønsted acid catalyzed [4+2] cycloaddition reaction with a variety of arylalkynes via ortho-quinone methides. A catalytic amount of trifluoromethanesulfonic acid effectively promotes the [4+2] cycloaddition reaction of salicylaldehydes with arylalkynes to afford the corresponding 2H-1-benzopyrans in good yields with high regioselectivities. Treatment of the cycloadduct 2,3-diphenyl-2H-1-benzopyran with some nucleophiles led to 4H-1-benzpyrans and 2H-1-benzopyran according to reagents. The present reactions provide versatile access to functionalized 2,3-disubstituted-2H-1-benzopyrans that would be a useful tool for the synthesis of biologically and photochemically active molecules.