N-Hydroxyphthalimide (NHPI) Promoted Aerobic Baeyer-Villiger Oxidation in the Presence of Aldehydes

摘要

Metal-free aerobic Baeyer-Villiger (BV) oxidation of ketones to lactones or esters in the presence of aldehydes promoted by N-hydroxyphthalimide (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.