Imidazo pyridines 3-

In 1998, three different research groups discovered a novel multi-component reaction almost simultaneously40. They found (partly by serendipity ) that when using 2-aminopyridines as the amine component in the Ugi four-component reaction (4CR), the formation of imidazo-pyridines was observed. The imidazo-pyridine is the product 

---

T. Granier, N. Panday, and A. Vasella, Structure-activity relations of imidazo-pyridine-type inhibitors of P-D-glucosidases, Helv. Chim. Acta, 80 (1997) 979-987. 

Several alkylcobaloximes have been degraded by acetic anhydride in pyridine to an imidazo-pyridine, and a key step in a complicated sequence is the migration of pyridine from cobalt to an activated ligand (Scheme 56).179... 

This reaction appears to be similar to the imidazo-pyridine formation mentioned above, most likely via a [5+1] insertion reaction of the isocyanide into the corresponding hydrazone. This reaction mechanism seems likely since only electron-rich aromatic hydrazines yielded cinnolines. The Ugi 4-CR reaction with phe-nylhydrazine is known and has been reported to give the expected Ugi-type 4-CR product. 

BZl and BZ2 (a2, a 3, and a5) sites. A two-dimensional NMR analysis (409) found that Zolpidem possessed only one family of conformations, in which the acetamide moiety was positioned 2 A above the plane of the imidazo-pyridine ring. This is consistent with the crystal structure of edpidem (399). Saripidem also exists in this conformation, which is presumed to impart BZl affinity. However, saripidem m exist in a second conformation in which the acetamide group is in the plane of the imi-dazopyridine system, and this conformation m confer BZ2 affinity. 

Methoxycarbonylamino-6-methylbenzyloxy)-2-methyl-3-(2-propynyl)-imidazo-[l,2-a]-pyridine has been investigated as an imidazo-pyridine derivative and an orally effective antiulcer agent potentially useful as an inhibitor of ATPase. The title compound has been obtained in... 

Fig. 6.13 Detectors arranged in series. (Reproduced with permission from G. A. Gross and A. Gruter, J. Chromatogr., 592, 271 (1992).) Condition sample, heterocyclic aromatic amines column, 25cmx4.6mm i.d. stationary phase, TSK gel ODS80, 5iam mobile phase, 1 ml min water with 0.01 M triethyla-mine, pH 3.2 or 3.6, and acetonitrile, gradient UV 263 nm and fluorescence detectors. Peaks 1 and 5 = pyrido-imidazoles 2 and 4 = imidazo-chinolines 3, 6, 7, 8 = imidazo-chinoxalines 9, 10, 11, 13, 14 = pyrido-indoles 12 = an imidazo-pyridine.

Ar = 2,4,6-(/-Pr)3C6H2 SCHEME 84 Pd-catalyzed synthesis of imidazo-pyridines/p)rrazines. 

Reviews have appeared dealing with the synthesis of 6i/-pyrido[4,3- ]-carbazoles, thieno-pyridines, and imidazo-pyridines (and their benzo-analogues) having a bridgehead nitrogen atom. ... 

Palmer AM, Nettekoven U. Preparation of tricyclic imidazo-pyridines by asymmetric ketone hydrogenation in the presence of ruthenium phosphino-oxazoline catalyst. Tetrahedron Asymm. 2007 18(20) 2381-2385. 

---