Reaction of l-Aryl-2-hydroxy-l-alkanone Dimethyl Acetal with Dihalotriphenylphosphorane

Abstract

The reactions of l-aryl-2-hydroxy-l-alkanone dimethyl acetal 1 with dibromotriphenyl-phosphorane 2 or dichlorotriphenylphosphorane 3 in the presence of pyridine at reflux temperature gave methyl 2-arylalkanecarboxylate 4. The acetals 1 having an electron-donating group on the aromatic ring gave 4 in 94~95% yield. On the other hand, the reaction of 1 with diiodotriphenylphosphorane 5 gave l-aryl-l-methoxy-2-alkanone 6 in a high yield (84~88%). It is assumed that the reactions of 1 with 2 or 3 proceed through an intermediate formed by the 1,2-migration of aryl group and the elimination of triphenylphosphine oxide from alkoxyphosphonium salt 7, and that the reaction of 1 with 5 proceeds through an oxirane formed by the elimination of methyl iodide and the phbsphine oxide from 7. © 1990, The Chemical Society of Japan. All rights reserved.