Ruthenium Complex-catalyzed Enantiotopos-differentiating Dehydrogenation from Diols

Abstract

Ru2Cl4((-)-DIOP)3(DIOP=2, 2-dimethyl-4, 5-bis(diphenylphosphinomethyl)-l, 3-dioxolane), in the presence of triethylamine, was found to be an efficient catalyst for the hydrogen transfer to alkenes from 1,4- or 1,5-diols which have the prochiral center or the meso structure to afford optically active γ- δ-lactones with the optical purity up to 16. 9%. This reaction belongs to the enantiotopos-differentiating reaction, in which one of the enantiotopic hydroxymethyl group of prochiral molecules is oxidized to give chiral lactones. This type of reactions has been rarely reported for homogeneous transition metal complex catalysis, whereas the reactions of the similar type have been extensively investigated for enzyme-catalyzed reactions. The chiral induction was directed by the position of the substituent(S) of diol, i.e. 3-substituted 1,5-diols gave (R)-δ-valerolactones and β, β-disubstituted 1,4- or 1,5-diols gave γ- or δ-lactones which have S-configuration at the carbon center adjacent to the carbonyl group. It was also found that the two distinct mechanisms of chiral induction took part in this reaction in a similar manner for the dehydrogenation of diols catalyzed by horse liver alcohol dehydrogenase; the first step is the selective dehydrogenation of one of the enantiotopic hydroxymethyl groups of a diol to give an optically active hemiacetal, and the second one is the subsequent selective dehydrogenation of one of the epimers of the hemiacetal to give the lactone (kinetic resolution). © 1985, The Chemical Society of Japan. All rights reserved.