434200 C-C Coupling through Direct Aldol Condensation Using Lewis Acid Zeolites

Wednesday, November 11, 2015: 9:50 AM
355A (Salt Palace Convention Center)
Jennifer Lewis, Stijn Van de Vyver and Yuriy Roman, Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MA

The development of biomass conversion schemes has led to considerable interest in aldol condensation, a key carbon-carbon (C-C) coupling reaction in organic synthesis. Aldol reactions are particularly important for transforming short-chain oxygenated molecules into fuels and value-added chemicals. Here, we show that Lewis acid zeolites Hf-, Sn-, and Zr-Beta catalyze the cross-aldol condensation of aromatic aldehydes with acetone. NMR studies with isotopically labelled molecules support a soft enolization pathway wherein the α-proton of acetone is transferred to the zeolite lattice, generating a metal enolate intermediate that can readily attack a carbonyl group to form a C-C bond. These C-C coupling reactions were conducted under mild conditions with near quantitative yields of the single cross-aldol condensation product for several substrates including the biomass-derived platform molecule 5-(hydroxymethyl)furan. Sn-Beta was also used to catalyze coupling of 1,3-dihydroxyacetone and formaldehyde through aldol addition followed by isomerization, dehydration, and keto-enol tautomerization to form α-hydroxy-γ-butyrolactone. Importantly, these Lewis acid zeolites maintain C-C coupling activity in the presence of water. Unlike traditional base catalysts, these materials are also active in acidic solutions.

Extended Abstract: File Not Uploaded