RUTHENIUM(II)-CATALYZED OPPENAUER-TYPE OXIDATION OF SECONDARY ALCOHOLS

Highly efficient ruthenium-catalyzed Oppenauer-type oxidations of seco ndary alcohols to ketones have been developed. The catalytic system co nsists of [(PPh(3))(3)RuCl2] (1) and K2CO3 or [(C(4)Ph(4)COHOCC(4)Ph(4 ))(mu-H)(CO)(4)Ru-2] (2) in refluxing acetone. The catalytic reaction is of high efficiency and permits a catalyst:substrate ratio of 1:1000 at 56 degrees C. In some cases the initial turnover rate exceeds 1500 h(-1). The reaction was found to be general and compatible with doubl e bonds and oxidation-sensitive aromatics. With some allylic alcohols, isomerization to saturated ketones took place. The reaction proceeds by ruthenium-catalyzed dehydrogenation of the alcohol and subsequent h ydrogen transfer to acetone. No primary kinetic isotope effect was obs erved for the catalytic reaction when alpha-deuterated 1-phenylethanol was employed as substrate (k(H)/k(D) = 1.1); this shows that beta-hyd ride elimination from a ruthenium alkoxide intermediate is not the rat e-limiting step.