Efficient isomerization of allylic alcohols to saturated carbonyl compounds by activated rhodium and ruthenium complexes

A range of readily available rhodium complexes of the general structures Rh (PPh3)(3)(+) PF6- and RhX(PPh3)(3) (X = H, Me, Ph) have been prepared and u sed in situ for the isomerization of allylic alcohols to their correspondin g saturated carbonyl compounds. The isomerization of octen-3-ol, selected a s a model, yielded octan-3-one in good yield. This reaction has been extend ed to the corresponding ruthenium complexes of the general structures [RuCl (PPh3)(3)](+) PF6-, RuXCl(PPh3)(3) and RuX2(PPh3)(3) (X = H, Me, Ph). It is noteworthy that many of these complexes have not been employed previously for this isomerization. The scope and efficiency of the process has been de monstrated by four representative complexes [RhH(PPh3)(3), RuH2(PPh3)(3), R uPh2(PPh3)(3), RuCl(PPh3)(3)(+) PF6-] with a wide variety of allylic alcoho ls. The reaction of primary allylic alcohols in the presence of RuCl(PPh3)( 3)(+) PF6- in methanol yields aldehydes protected as their methyl acetals. Deuterium labelling experiments are in agreement with a 1,3-hydride shift m echanism.