Enantioselective Flow Synthesis of Rolipram Enabled by a Telescoped Asymmetric Conjugate Addition-Oxidative Aldehyde Esterification Sequence Using in Situ -Generated Persulfuric Acid as Oxidant.

A novel approach is reported for the enantioselective flow synthesis of rolipram comprising a telescoped asymmetric conjugate addition-oxidative aldehyde esterification sequence followed by trichlorosilane-mediated nitro group reduction and concomitant lactamization. The telescoped process takes advantage of a polystyrene-supported chiral organocatalyst along with in situ -generated persulfuric acid as a robust and scalable oxidant for direct aldehyde esterification. This approach demonstrates significantly improved productivity compared with earlier methodologies while ensuring environmentally benign metal-free conditions.