Imidazo pyridine. base-catalyzed

The imidazo[4,5-J][l, 2]diazepine diribonucleoside (585) upon treatment with methanolic ammonia at room temperature undergoes a base-catalyzed ring contraction of the diazepine ring to give 4-amino-1,3-dihydro-l,3-bis(/ -D-ribofuranosyl)imidazo[4,5-c]pyridin-2-one (586) (58%) (Scheme 74) <86Ti5ii>. 

In the presence of a coupling reagent (POB), the o-arabinohexulosonic acid derivative 220 condensed with 2,3-diaminopyridines to provide the amides 221. The 2-()8-D-pentopyranosyl)imidazo[4,5-h]pyridines 222 were then obtained by mild base-catalyzed cyclodehydration of 221 [80JCS(P1)2683] (Scheme 65). 

Various imidazo[l,5-a]imidazoles (35), imidazo[l,5-a] pyridines (36), and imidazo[5,l-a]isoquinolines (37), important ligands or precursors to pharmaceuticals, can be constructed wa copper-catalyzed heterocyclization ofSchiff s bases. A stepwise cycloaddition between azides and terminal alkynes is also catalyzed by copper salts in what has now been termed click chemistry, producing 1,4-disubstituted triazoles (38) in excellent yields. 

Doring et al. developed a CUCI2 -catalyzed synthesis of imidazo[l,5- ]pyridines, imidazo[l,5- ]imidazoles, and imidazo[5,l- ]isoquinolines starting from Schiff base which could be prepared readily from the appropriate aldehydes and primary amines [97] (Scheme 8.56). 

---