Authors:Kimitada Terao, Yasuhiro Nishiyama and Kiyomi Kakiuchi
An asymmetric Paternò–Büchi-type photoreaction between 2,3-dimethyl-2-butene and benzoylformic acid ester with a chiral menthyl auxiliary was studied in a continuous-flow microcapillary reactor. The fluorinated ethylene propylene (FEP) microcapillary reactor using normal one-layer flow mode gave oxetane products with better efficiency than the batch system. In addition, the slug flow mode in microcapillary reactor using inactive reagent, N2 gas or H2O, improved the reaction efficiency dramatically because of synergistic light dispersion, stirring and thin layer film effects. The reaction efficiencies under each condition were discussed as energy efficiencies calculated from reactors' parameters.
The diastereodifferentiating [2+2] photocycloaddition of a chiral cyclohexenone with cyclopentene was performed in supercritical carbon dioxide (scCO2) using a flow microreactor. In all cases examined, the microreactor gave higher conversions than the batch system because of the very short path length of the microreactor. Additionally, by using the microreactor, accurate temperature control produced higher diastereoselectivity. These distinguished findings can be attributed to the synergistic effect of superior light penetration in the microreactor and the unique solvent property (clustering effect) of scCO2.