ASYMMETRIC HYDROGENATION OF OLEFINS WITH APROTIC OXYGEN FUNCTIONALITIES CATALYZED BY BINAP RU(II) COMPLEXES

Cyclic alpha,beta-unsaturated ketones, alkylidene lactones, and alkenyl ethers have been hydrogenated in high enantiomeric excesses by use of BINAP-Ru(II) complexes (BINAP = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl) as catalysts. 2-Alkylidenecyclopentanones were hydrogenated in the presence of [RuCl(BINAP)(benzene)]Cl, Ru2Cl4(BINAP)2(NEt(3)), or Ru(OCO CH3 )(2)(BINAP) in up to 98% ee, while in the case of 2-benzylidene- and 2-(3-phenylpropylidene)cyclopentanones, enantiomeric excesses of the hydrogenation were below 50% under the same conditions. The sense of asymmetric induction as well as the enantioselectivity (95% ee) obtained in the hydrogenation of (E)-2-propylidene-gamma-butyrolactone were the same as those of the (Z)-isomer. Lactones, 2- and 4-alkylidene-gamma-butyrolactones, were converted to the corresponding saturated gamma-butyrolactones in 95% ee. Hydrogenation of diketene with the catalytic system derived from {RuCl[(S)-BINAP](benzene)}Cl and triethylamine or complex Ru2Cl4[(S)-BINAP](2)(NEt(3)) established a new synthetic route to (R)-4-methyl-2-oxetanone, a promising monomer of biodegradable polymers, in up to 97% selectivity and 92% ee. Alkenyl ethers, 2-methylenetetrahydrofuran, and 2-methyl-3,4-dihydrofuran have also been hydrogenated to give 2-methyltetrahydrofuran in 91 and 87% ee, respectively.