(R)-3-(3,5-Diphenylimidazolidin-1-yl)oxazolidin-2-one 1a was utilized as the model substance for investigating different reactivities in organic microdroplets and bulk phase. The reactant 1a (5 mmol L -1 ) and sulfuric acid (11 mmol L -1 ) was prepared in acetonitrile. The prepared reaction solution was then introduced into a sonic sprayer to generate organic microdroplets at a flow rate of 15 μL min -1 , and the resulted product from the sprayed microdroplets was collected for 10 min (see the setup in Figure ). After exaction with dichloromethane and washing with aqueous sodium bicarbonate, the organic phase was analyzed by HPLC for estimating reaction yields. As shown in Figure , a vicinal diamine product 2a was generated in the microdroplet reactor due to double C-N bond cleavage of 1a, where formaldehyde was formed from the eliminated methylene group (see a plausible reaction mechanism in Scheme 5). We further carried out this conversion under various reaction conditions 1a concentration (5-100 mmol L -1 ), sulfuric acid equivalent (0.18-36.8 equiv.), spray flow rate (5-300 μL min -1 ), reaction temperature (25-60 °C) and organic solvents, see the details in the following optimization section), and all these microdroplet reactions offered the same product 2a with only difference in reaction yields. In addition, the product 2a formed by organic microdroplet chemistry was in high stereoselectivity (91% ee) (see the chirality estimation in supporting information S9), which is attractive to the discovery of chiral drugs.