Alkenes Made Simple From Biomass Polyols

A hot topic in synthetic organic chemistry these days is creating reactions that more efficiently convert biomass-derived carbohydrates into feedstock chemicals and fuels. One of the latest developments on this front comes from Robert G. Bergman, Jonathan A. Ellman, and coworkers of the University of California, Berkeley, who have devised a new deoxygenation method to convert polyhydroxyl compounds such as glycerol and erythritol into olefins (Chem. Commun., DOI: 10.1039/b907746d). The high oxygen content of cellulose, sugars, and oils derived from plants prevents them from being directly used as chemicals and fuels. The UC Berkeley researchers explored using formic acid as a simple catalyst to remove some of the oxygen by dehydrating a selection of polyols. To the chemists' surprise they discovered a new reaction pathway in which the acid directly removes two adjacent hydroxyl groups via a cyclic carbocation intermediate, replacing the hydroxyl groups with a C–C bond to form an alkene. This didehydroxylation reaction has promise as a mild and inexpensive one-pot, solvent-free procedure that could become standard chemistry in biorefineries, which are ultimately expected to replace oil refineries.