Remarkable activity of the isomerization catalyst [RuCp(PPh 3) 2](OTs) in O-allylation of phenol with allyl alcohol

The highly active isomerization catalyst [RuCp(PPh 3) 2](OTs) changes its catalytic action to the selective O-allylation of phenols with allyl alcohol upon addition of a catalytic amount of a strong acid. It was surprisingly found that the highly active allyl alcohol redox isomerization catalyst [RuCp(PPh 3) 2](OTs) upon addition of a catalytic amount of a strong acid can change its catalytic action fully to the selective O-allylation of phenols with allyl alcohol. High turnover numbers (75,000 based on phenol; 200,000 based on allyl alcohol) are reached, and the catalyst is very stable in the presence of substrate. Addition of triphenylphosphine to the reaction mixture does not lead to further stabilization of the catalyst; instead, the free phosphine is rapidly allylated, thereby consuming the acid, which deactivates the catalytic system for allylation reactions. This catalyst with monodentate phosphine ligands is superior in both activity and selectivity to similar catalysts with bidentate phosphine ligands. Apart from phenols, also thiophenol can be efficiently allylated to form allyl phenyl sulfide.