The mechanism of aqueous ruthenium(II)-catalyzed olefin isomerization

Abstract

Olefin isomerization of allylic ethers and alcohols is catalyzed by Ru^(II)(H_2O) (tos = p-toluenesulfonate) (1) under mild conditions in aqueous solution to yield the corresponding carbonyl compounds. Non-allylic olefins are also isomerized, although homoallylic alcohols exhibit stability toward isomerization. An exclusive 1,3-hydrogen shift is observed in the isomerization of allyl-1,1 d_2 alcohol to propionaldehyde-1,3-d_2 and allyl-1,1-d_2 methyl ether to 1-propenyl-1,3-d_2 methyl ether by 1 in aqueous solution. The presence of crossover products from the isomerizations of mixtures of (a) allyl-3-^(13)C alcohol and allyl-1,1-d_2 alcohol and (b) allyl-1 ,1-d_2 methyl ether and allyl ethyl ether demonstrates that the isomerization of both alcohols and ethers occurs via intermolecular hydrogen shifts. A modified metal hydride addition-elimination mechanism involving exclusive Markovnikov addition to the double bond directed by the oxygen functionality of the substrate has been proposed.