N-hydroxyphthalimide/cobalt(II) catalyzed low temperature benzylic oxidation using molecular oxygen

A variety of(substituted) aryl glyoxylates is formed in good to excellent y ield under very mild conditions by direct oxidation of the corresponding ar ylacetic esters or mandelic acid esters with molecular oxygen and N-hydroxy phthalimide/cobalt(II) acetate as catalyst. Heteroaromatic analogs are more difficult to oxidize with this system. The effect of substitution in the a romatic ring of N-hydroxyphthalimide on the oxidation of ethylbenzene has b een studied. Electron withdrawing substituents accelerate the oxidation of ethylbenzene and promote the formation of acetophenone. Electron donating s ubstituents lead to decreased rates of oxidation and enhance the selectivit y for 1-phenylethanol. (C) 2000 Elsevier Science Ltd. All rights reserved.