Notes on acetal formation in stereoselective hydrogenation of methyl-3-oxobutyrate on Ru-BINAP chiral complex

Performance of the cationic chiral Ru-BINAP complex in asymmetric hydrogenation of methyl-3-oxobutyrate (methylacetoacetate) in methanol was studied. Effects of temperature, pressure and the content of water on its activity and enantioselectivity were discussed. Attention was paid to the role of water in respect of the enhanced acetal formation in the presence of methanol. A simple approach to limit the content of acetal was introduced. The role of water addition was clarified. Tetrahydrofuran as a solvent system (with the addition of methanol or water) was also tested to minimize the acetal presence in the reaction mixture. In parallel the influence of oxygen on the catalyst stability was examined.