NHC-catalyzed formal [3+3] annulations of -acetoxy allenoates for the synthesis of 4H-pyran derivatives

Herein, an N-heterocyclic carbene (NHC) catalyzed formal [3 + 3] annulation of & delta;-acetoxy allenoates with 1C,3O-bisnucleophiles for the construction of 4H-(fused)pyrans has been developed. This protocol provides a facile method to synthesize highly functionalized 4H-pyrans and has a broad substrate scope (30 examples, up to 77% yield).