Copper-catalyzed [3 + 2 + 1] annulation for functionalized pyridines as potent and dynamic UV absorbers

Abstract

A novel Cu(OTf)₂-catalyzed [3 + 2 + 1] annulation of chromenone carbaldehydes or benzochromenone carbaldehydes with β-enamino substrates and ammonium acetate is developed. This protocol provides a facile and efficient one-pot procedure for the construction of diverse and functionalized pyridines bearing a variety of substituents. This [3 + 2 + 1] annulation proceeds via a cascade aldol-type reaction, deprotonation and protonation, Michael addition and ring opening, and intramolecular Michael addition and heteroaromatization. The synthesized compounds exhibited potent and dynamic UV absorption for broad spectrum coverage.