Accelerated photocatalytic [3+2] cycloaddition of phenols and olefins in nESI-MS

Abstract The photocatalytic [3+2] cycloadditions of phenols and olefins are normally limited by the relatively tedious process. Herein, based on accelerated microdroplet reactions, a nano-electrospray ionization (nESI) was constructed for online acceleration of photocatalytic [3+2] cycloaddition between phenols and olefins. As demonstrated, the high reaction rates were obtained by nESI tips with smaller orifice inner diameter and the electrode closed to the nESI tip. These were further confirmed by the calculations on the conversion ratios and apparent acceleration factors. Meanwhile, the important intermediates (especially short-lived radicals) were recorded by virtue of the online monitoring of nESI mass spectrometry (MS). Subsequently, the dynamic information of substrates, intermediates and products were examined. Therefore, the mechanism of photocatalytic [3+2] cycloaddition reactions between phenols and olefins was proposed. This work not only enlarges the application of microdroplet synthesis, but also would provide a possible perspective for accelerating photocatalytic reactions and mechanism examinations.