Ruthenium(II)‐Catalyzed Oppenauer‐Type Oxidation of Secondary Alcohols

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Abstract
Highly efficient ruthenium‐catalyzed Oppenauer‐type oxidations of secondary alcohols to ketones have been developed. The catalytic system consists of [(PPh3)3RuCl2] (1) and K2CO3 or [(C4Ph4COHOCC4Ph4)(μ‐H)(CO)4Ru2] (2) in refluxing acetone. The catalytic reaction is of high efficiency and permits a catalyst: substrate ratio of 1:1000 at 56 °C. In some cases the initial turnover rate exceeds 1500 h‐1. The reaction was found to be general and compatible with double 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 hydrogen transfer to acetone. No primary kinetic isotope effect was observed for the catalytic reaction when α‐deuterated 1‐phenylethanol was employed as substrate (kH/kD=1.1); this shows that β‐hydride elimination from a ruthenium alkoxide intermediate is not the rate‐limiting step.

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