Basic anion-exchange resin catalyzed aldol condensation of aromatic ketones with aldehydes in continuous flow

A general method for the aldol condensation of aromatic ketones with aldehydes was developed under continuous-flow conditions using a commercially available, strongly basic anion-exchange resin (A26) as catalyst. This procedure, in addition to exhibiting a wide substrate scope, promoted carbon–carbon bond formation under mild conditions using a quasi-stoichiometric ratio of starting reagents with good to excellent yields, thereby forming a limited amount of waste and allowing the process to be applied to sequential-flow systems. A proof of concept was developed in the first fully heterogeneously catalyzed two-step flow synthesis of donepezil, which is a blockbuster commercial anti-Alzheimer’s drug.