Synthesis of Ethers by GaBr3-Catalyzed Reduction of Carboxylic Acid Esters and Lactones by Siloxanes

Ethers were synthesized by reduction of the respective esters catalyzed by gallium bromide (GaBr3) and using siloxanes, preferentially 1,1,3,3-tetramethyldisiloxane, as reductant. Methyl oleate, triglycerides, that is, tributyrine and glyceryl triundec-10-enoate as well as gamma- and delta-lactones were converted into the respective ethers in high to moderate yields. gamma-Lactones were reduced with high selectivity in the presence of a methyl ester functionality. The reduction has been carried out at room temperature or moderately elevated temperature of up to 60 degrees C using stoichiometric amounts of the reductant and 0.005-0.01 equiv of GaBr3 as catalyst per ester functionality without any solvent added. After a reaction time of 1-4 h the conversion of the substrate was 100 %. The product was separated from polymeric siloxanes formed as coupled product by simple distillation.