Phosphine-Catalyzed Stereoselective Tandem Annulation Reaction for the Synthesis of Chromeno[4,3-b]pyrroles.

A phosphine-catalyzed tandem cyclization reaction has been developed to provide a series of chromeno[4,3-b]pyrrole derivatives, which contain three consecutive asymmetric centers. The reaction has a good yield, excellent stereoselectivity, and Z/E selectivity. The new method is simple, requires only mild conditions, and shows tolerance for various functional groups. Similarly, this reaction can be catalyzed by a chiral phosphine catalyst to achieve asymmetric synthesis.