Epoxidation of hydroxy and acetoxy derivatives of dicyclopentadiene with hydrogen peroxide catalyzed by (C5H5N+(CH2)15CH3)3(PMo12O40)3-.

Abstract

Hydroxy and acetoxy derivatives of dicyclopentadiene (DCP) were regio- and stereoselectively epoxidized in good yields with H2O2 in the presence of a quaternary ammonium salt of heteropoly acid, [C5H5N+(CH2)15CH3]3[PMo12O40]3- (CPMP), under mild conditions. In the epoxidation of hydroxy derivatives of DCP, the orientation of the hydroxy group was found to be an essential factor which determined the selectivity of the reaction. The regio- and stereoselectivities in the epoxidations of 1α, 8a and 8s-hydroxydicyclopentadienes were explained by consideration of the transition state geometry between the oxidizing species anchored to the hydroxy group of substrate and the olefinic π-bond. However, the oxidation of 1β-hydroxydicyclopentadiene, in which the molybdenum species is difficult to occupy syn-geometry as a preferred transition state geometry, gave conjugated enone 5 exclusively. The acetoxy substituent introduced to DCP exerted steric hindrance rather than a directing effect in the epoxidation. Therefore, the regioselectivity in the epoxidation of acetoxy derivatives appeared to be the opposite to that of hydroxy derivatives.