Recently, the pharmaceutical industry has increased interest in continuous flow processes because of drastically shortened reaction time, effective heating with tubular reactors, minimized hazardous chemical exposure to the user, and ultimately, lower production costs. Here we describe a multistep continuous flow synthesis of diphenhydramine, a first-generation antihistamine and active pharmaceutical ingredient of Benadryl<sup>®</sup>. The three-step synthesis was successfully executed using a commercially available flow chemistry system and using an in-house continuous synthesis system. The intermediates between each step were not isolated, and the purity of the product was monitored in-line with optical detectors.

Multi-step continuous flow synthesis of diphenhydramine

253rd National Meeting (2017)

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