The Reaction of 3‐(Dimethylamino)‐2 H ‐azirines with 2,3‐Pyridinedicarboximide

Reaction of 2,2‐dialkyl‐3‐(dimethylamino)‐2 H ‐azirines 1a and 1b with 2,3‐pyridinedicarboximide ( 4 ) in MeCN or DMF at room temperature yielded two regioisomeric tricyclic 1:1 adducts, the azacyclols 11/12 and 16/17 , respectively ( Schemes 3 and 4 ). The structure of 12 was established by X‐ray crystallography. Methanolysis of 11/12 and 16/17 led to mixtures of methyl [4, 4‐dialkyl‐5‐(dimethylamino)‐4 H ‐imidazol‐2‐yl] pyridine carboxylates 13/14 and 18/19 , respectively. The structure of compound 14 is closely related to that of the powerful herbicide 9 ( Scheme 9 ), i.e. the described reactions offer a new synthetic approach to this class of compounds. A mechanistic interpretation for the formation of regioisomeric 1:1 adducts as well as methyl (imidazol‐2‐yl) pyridine carboxylates is depicted in Scheme 5 .