Quick execution of [2+2] type photochemical cycloaddition reaction by continuous flow system using a glass-made microreactor

A photochemical [2+2] cycloaddition reaction was executed in a microflow system using glass-made microchannels having 1000-mum width and 500-mum depth. The reaction of cyclohexenones with vinyl acetates in a microflow system under irradiation (300 W, Hg lamp) gave [2+2] cycloaddition products in good yield with a residence time of 2h, which is a remarkably shortened reaction time compared with a batch system using the same light source.