X-Ray crystallographic evidence for a vinylogous anomeric effect in benzotriazole-substituted heterocycles

Structural evidence for the existence of a ‘vinylogous’ anomeric effect is presented for a series of 4H-4-benzotriazolyl-2,6-diarylpyrans 1a,b and for their benzo-fused derivatives 2–5 and nitrogen analogue 6. X-Ray crystal structure analyses reveal changes in the geometry of the central ring and exocyclic C–N bond, which are discussed in terms of an interaction of the benzotriazole fragment with a heteroatom through four bonds.