Cyclization of tautomeric 1,5-dinitrile systems with hydrogen halides: A definitive mechanistic rationalization?

A new mechanistic rationalization for the cyclization with hydrogen halides of tautomeric 1,5-dinitriles of general structures (10) (Z = N), (14) (Z = C-CN), (16) (Z = N), and (18) (Z = C-CN) is proposed (Scheme 5). In such rationalization, three factors play a major role on the direction of cyclization: Position of the equilibrium of the tautomeric 1,5-dinitrile system, relative basicity of the cyano groups involved, and planarity of the reaction zone.