Oxo-Rhenium-Catalyzed Deoxydehydration of Polyols with Hydroaromatic Reductants

Several dihydroaromatic compounds are shown to be effective reducing agents in the oxo-metal-catalyzed deoxydehydration of diols and polyols to produce olefins and the corresponding arenes. NH4ReO4 and MeReO3 are active catalysts for the reactions. The most effective of the hydroaromatic reductants is indoline, which is oxidized to indole. Yields for a variety of diols and polyols range from 35% to 99%. Two hydrogen donors, 1,3-cyclohexadiene and dihydroanthracene, engage in tandem DODH/cycloaddition reactions. Competition experiments show that indoline is more reactive than representative alcohols in H-transfer. Indoline is shown to reduce MeReO3 to MeReO2 via an isolable adduct, MeReO3(indoline) (4), which has been structurally characterized and is suggested to be an intermediate in the catalytic DODH process.