A series of [2+2]-photocycloadditions of 1,4-naphthoquinone with various alkenes and diphenylacetylene were investigated under batch and continuous-flow conditions. Acetone-sensitization furnished the corresponding photoadducts in good to excellent yields and purities. Compared to batch operations that demanded exhaustive irradiation times of 10-13 h, the flow process generally gave superior conversions and subsequently yields with a residence time of just 60 min. The structures of several photoaddition products were further determined by crystal structure analysis.
Keywords: continuous-flow photochemistry; cyclobutanes; naphthoquinones; photocycloaddition.