The heat of reaction, calculated with the heat flow during the reaction, was 161 kJ/mol (See Supporting Information File 1). The time course of the heat of reaction revealed that this reaction was almost a zero-order reaction as shown by the red line in Figure , which did not depend on the concentration of 1a (Figure ). As shown in entries 3 vs 4 in Table , the rate-determining step is considered to be the catalytic cycle A in Scheme 1, which is consistent with the consideration from the time course of the heat of reaction. The adiabatic heating was calculated to be 138 K (based on the input amount of the starting material 1a) (See Supporting Information File 1). To suppress the increase of the internal temperature, the amount of AcOH was increased by 40 times (from 3 mL/g to 120 mL/g) for the following evaluation of the reaction rate under flow conditions. This dilution suppressed the adiabatic heating to less than 5 K, and the reaction rate could be more precisely evaluated.