Selectively aerobic oxidation of C=C and allylic C-H bonds in α-pinene over simple metalloporphyrins

Simple metalloporphyrins (TPPMnCl, TPPCoCl, TPPFeCl, TPPNi, TPPCu or TPPZn) were employed as the catalysts for the aerobic oxidation of alpha-pinene in the absence of co-catalyst and solvents, and the catalytic selectivity of metalloporphyrins for aerobic oxidation of double bond and allylic C-H of a-pinene was investigated. The research results indicate that the reaction temperature, the metal nuclei, and peripheral substituents of the metalloporphyrins influence the catalytic selectivity of metalloporphyrins in the aerobic oxidation of alpha-pinene. Over TPPMnCl catalyst, the selectivity regarding the oxidation of C=C bond increased with decreasing temperature. Among various metalloporphyrins, TPPMnCl presented the largest selectivity regarding the oxidation of C=C bond and TPPFeCl the largest selectivity regarding the oxidation of allylic C-H bonds. With increasing the electron-donating abilities of the peripheral substituents in T(p-X)PPMnCl (X=Cl, CH3, OCH3, OH), the selectivities regarding the oxidation of C=C bond decreased. The results may provide an additional evidence for the stepwise mechanism through a radical intermediate. (C) 2004 Elsevier B.V. All rights reserved.