Solvents such as DMSO and DMF are excellent for organic reactions with inorganic salts because of their dipolar, aprotic and inexpensive character. But their high boiling points preclude benign separation and recycle. We report piperylene sulfone, a labile DMSO substitute, which undergoes a retro-cheletropic reaction into volatile species under modest conditions, and which can easily be collected and converted back into piperylene sulfone via a concerted reaction for re-use. This provides the opportunity for facilitating recovery and recycling of both catalyst as well as the solvent itself.

We have investigated the use of piperylene sulfone to couple separation and solvent and catalyst recycle with many reactions. As one example, we compare here its use for catalytic hydrogen transfer reactions with other organic solvents (DMSO, DMF, THF, acetone, toluene) and water. We reduced a series of aromatic ketones to their corresponding alcohols to demonstrate the stability to various functional groups. In all the cases, both a high conversion and enantiomeric excess were observed. The initial rate of the reduction reaction of acetophenone in piperylene sulfone was higher than in the organic solvents studied but lower than in water. This solvent was successful as an immobilization medium for catalyst recycle as well.