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dichloroethane (20 mL) were placed into a three-necked round bottom flask (50 mL) equipped with an oxygen balloon and a magnetic stir bar. The mixture was stirred at 40°C for 24 hours. The reaction was monitored by GC instrument. The conversion was calculated on the basis of the peak area ratio of cyclohexane against the internal standard, biphenyl. The product yields were calculated on the basis of the peak area ratio of cyclohexanol, cyclohexanone, and ɛ-caprolactone against the internal standard. Control experiment was conducted in the absence of NHPI.General EPR experiments in different solvents. To a 25 mL Schlenk tube with a magnetic stirrer was added 0.2122 g (2 mmol) of benzaldehyde, 0.0163 g (0.1 mmol) of NHPI and 10 mL of 1,2dichloroethane (DCE). The mixture was stirred at 40°C for 30 min at atmospheric pressure. Thereafter, EPR was measured immediately. The EPR spectra of the reaction solution were obtained by using a computer controlled X-band (9.5 GHz) EPR spectrometer (Bruker A300). The solvent DCE was replaced by CH 3 CN and Toluene. Control experiments were conducted in the absence of benzaldehyde in different solvents. General EPR experiments with NHPI.To a 50 mL three-necked glass flask fitted with a water cooled reflux condenser, a magnetic stir bar and an oxygen balloon was added 0.4245 g (4 mmol) of benzaldehyde and 20 mL of 1,2-dichloroethane (DCE). The mixture was stirred at 40°C for 30 min at atmospheric pressure. Then 0.0326 g (0.2 mmol) of NHPI was added into the mixture and the mixture was stirred for another 30 min. The EPR spectra of the reaction solution (Figure 1(c), green) were obtained by using a computer controlled X-band (9.5GHz) EPR spectrometer (Bruker A300). Thereafter, EPR was measured immediately upon addition of 0.168 g (2 mmol) of cyclohexane into the reaction system (blue). The reaction was continued for 2 h before measuring EPR (red).

Metal-free aerobic Baeyer-Villiger (BV) oxidation of ketones to lactones or esters in the presence of aldehydes promoted by Nhydroxyphthalimide (NHPI) has been developed. The reaction proceeded under mild conditions with excellent selectivity and high yields. Compared with the methods that use metal complexes as catalysts, this strategy not only showed good environmental advantages, but also increased aldehyde efficiency up to 84 %. Control experiments indicated that NHPI accelerated the oxidation of aldehydes to peroxy acids but did not improve the BV oxidation while peroxy acids were already generated. Peroxy acids generated from aldehydes in situ were the key intermediates, and the phthalimide-N-oxyl radical (PINO) contributed to high aldehyde efficiency by stabilizing the radical species, which are necessary for the chain propagation reactions. This study may offer some useful strategies for new transition metal-free catalytic aerobic oxidation reactions in which aldehydes act as sacrificial agents.

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