Organorhenium Catalysts

The application of rhenium compounds to synthetic organic reactions has progressed rapidly in 1990's while a variety of transition metal compounds, such as Pd, Ru and Ni complexes etc., which have been utilized since the 1950's. Characteristics of the organorhenium reactions are being discovered and applications for rhenium compounds such as 1 and 2¹⁾ are being developed.

The rhenium reagent 1 is used with hydrogen peroxide for catalytic oxidation reactions. For example, oxidation of olefins using a catalytic amount of 1 proceeds smoothly at room temperature and affords the corresponding epoxides in high yields.^2a) It is also applied to oxidizing phenols to quinones,^2b) benzaldehydes to phenols,^2c) sulfide to sulfoxides^2d) and tertiary carbon to tertiary alcohols.^2d)

The rhenium reagent 2, which is different from the homologous premanganates, is not capable of oxidizing alcohols nor olefins. However, 1,3-rearrangement of allylic and propargylic alcohols occurs in the presence of a catalytic amount of 2 and p-toluenesulfonic acid.³⁾ Furthermore, the combined use of 2 and a protic acid is quite effective catalyzing the Beckmann Rearrangement.⁴⁾