In fact, dipolar, aprotic solvents such as DMSO and DMF are excellent for organic reactions with inorganic salts because they are inexpensive and dissolve disparate materials. 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 already investigated the use of piperylene sulfone to couple separation and solvent and catalyst recycle with many reactions. In nucleophilic substitution reactions it gives rates comparable to those in DMSO. We show TEMPO oxidations of alcohols in piperylene sulfone with higher turn over frequency than DMSO and multiple recyles. Other examples include asymmetric transfer hydrogenation in piperylene sulfone and sulfone induced in situ acid catalysis. Here we show new opportunities for this solvent in the pharmaceutical industry.