Deoxygenation of Epoxides with Hexamethyldigermane Catalyzed by Au Nanoparticles on TiO₂

Abstract

Mono-and disubstituted epoxides undergo quantitative deoxygenation into the corresponding alkenes by hexamethyldigermane (Me 3 GeGeMe 3 ) in the presence of 1 mol% of supported Au nanoparticles on TiO 2 , with digermane being transformed into the corresponding digermoxane. Tri-and tetrasubstituted epoxides react either poorly or remain intact, allowing thus the selective intermolecular deoxygenation of a monosubstituted epoxide in the presence of a highly substituted one. Stereoisotopic studies and Hammett-type kinetics indicate a dipolar transition state of the deoxygenation process, whose degree of polarity profile depends on the substituents. For alkyl-substituted epoxides the deoxygenation is almost stereospecific (retention of configuration), while for the aryl-substituted ones, in which the dipolar character is more profound, substantial loss of stereospecificity is observed.