Imidazopyridine synthesis pyridine

Imtdazo[4,5-c]pyridtne, 4,5,6,7-tetrahydro-synthesis, 5, 623, 640, 641 Imidazo[4,5-c]pyridine-6-carboxylic acid, 4,5,6,7-tetrahydro-synthesis, 5, 623, 641 Imidazopyridines as anthelmintic, 1, 202 synthesis, 5, 462 Imidazo[l,2-n]pyridines deuterium exchange, 5, 611 diazo coupling, 5, 614 Dimroth rearrangement, 5, 613 halogenation, 5, 611 hydrogenation, 5, 614 Mannich reaction, 5, 612 nitration, 5, 612 1-oxides... 

The synthesis of zolpidem began with an alkylation/condensation reaction of amino-pyridine 5 and bromide 6 to give imidazopyridine 7 (Scheme 15.1). Mannich-type reaction with formaldehyde and dimethylamine provided 8. Treatment of 8 with methyliodide to form the quaternary salt 9, followed by reaction with sodium cyanide, gave 10. Acidic hydrolysis followed by reaction of the resultant acid 11 with carbonyldiimidazole (GDI) and dimethylamine afforded zolpidem (1) in 46% overall yield (George et al., 1991 Rossey and Long, 1988). 

A catalytic Fe(lll)/Fe(ll) redox cycling approach to imidazopyridines has also been reported for the synthesis of imidazo[4,5-f]pyridines (Equations 41 and 42) <2000S1380>. 

Imidazolium ligands, in Rh complexes, 7, 126 Imidazolium salts iridium binding, 7, 349 in silver(I) carbene synthesis, 2, 206 Imidazol-2-ylidene carbenes, with tungsten carbonyls, 5, 678 (Imidazol-2-ylidene)gold(I) complexes, preparation, 2, 289 Imidazopyridine, in trinuclear Ru and Os clusters, 6, 727 Imidazo[l,2-a]-pyridines, iodo-substituted, in Grignard reagent preparation, 9, 37—38 Imido alkyl complexes, with tantalum, 5, 118—120 Imido-amido half-sandwich compounds, with tantalum, 5,183 /13-Imido clusters, with trinuclear Ru clusters, 6, 733 Imido complexes with bis-Gp Ti, 4, 579 with monoalkyl Ti(IV), 4, 336 with mono-Gp Ti(IV), 4, 419 with Ru half-sandwiches, 6, 519—520 with tantalum, 5, 110 with titanium(IV) dialkyls, 4, 352 with titanocenes, 4, 566 with tungsten... 

Imidazopyridines (IPs) may be synthesized from pyridine or imidazole derivatives by building up the second ring, and also by ring transformations from the other heterocyclic compounds. However, these methods are not of equal efficiency, and the most important preparative procedures utilize amino derivatives of pyridine as initial compounds for IP s synthesis. The main IP s precursors are o-diaminopyridines (o-DAP). 

Isoelectronic replacement of a carbanionic carbon by a hetero atom gives much more stable compounds such 5,5-bicyclic aromatic systems have received considerable attention pyrrolo[2,l-b]thiazole is one such example. Although we have not had sufficient space to describe these in this short chapter, their properties and synthesis follow the general principles discussed for example, imidazothiazoles are prepared from substituted thiazoles in a way analogous to the preparation of imidazopyridines, from substituted pyridines. 

Labeled heterocyclic systems of the imidazopyridine type are accessible from halo [ " ]-acetates. For example, the reaction between 2-aminopyridine and chloro[2- C]acetic acid produced (2-imino-l,2-dihydropyridin-l-yl)[2- C]acetic acid (1411 in 76% yield (Figure 6.46). Treatment of 141 with POCI3 induced cyclization and chloro-dehydration to furnish 2-chloro[3- C]imidazo[l,2-a]pyridine (1421 in 99% yield. The latter was a key intermediate in the synthesis of the carbon-14-labeled herbicide MON 37500 (1431. ... 

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