NHC-Catalyzed [2 + 4] Annulation of Alkynyl Ester with Chalcone.

An NHC-catalyzed [2 + 4] cyclization of alkynyl ester with α,β-unsaturated ketone to form a pyran scaffold was developed successfully. The cheap and easily available starting materials, mild reaction conditions, moderate to excellent yields, and high atom economy make this strategy attractive for the syntheses of highly substituted 4 H -pyran derivatives.