Imidazo pyridine-2-ones

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. 

According to the third criterion, quinoxaline is the base component The heterocycle imidazole, which is fused to the base component, is numbered in the usual way the pyridine ring, however, is denoted by 1, 2, and so on, and it is not necessary to mark the double bonds. Pyrido[T,2 l,2]imidazo denotes one ring fusion, imidazo[4,5-b]quinoxaline the... 

Imidazo[4,5-6]pyridin-5(4H)-one, 6-ethoxycarbonyl-3-methyl-2( 1 H)-thioxo-synthesis, 5, 639... 

Reaction of 2 equiv of 2-aminopyridines with 2-hydropolyfluoroalk-2-anoates 351 in MeCN in the presence of NEts at 90 °C for 50 h afforded a mixture of the isomeric 2-oxo-2H- and 4-oxo-4//-pyrido[l,2-n]pyrimidines 110 and 111. Reaction of 3 equiv of 2-amino-pyridines and 2-hydropoly-fluoroalk-2-enoates 351 in MeCN in the presence K2CO3 could be accelerated by ultrasonic irradiation (125W). 2-Amino-6-methylpyridine yielded only 2-substituted 6-methyl-4//-pyrido[l,2-n]pyrimidin-4-ones 111 (R = 6-Me), whereas 2-amino-5-bromopyridine gave a mixture of 7-bromo-4//-pyrido[l,2-n]pyrimidin-4-one (111, R = 7-Br, R = CF2C1) and 2-(chlor-o,difluoromethyl)-6-bromoimidazo[l, 2-n]pyrimidine-3-carboxylate in 44 and 8% yields, respectively (97JCS(P 1)981). Reactions in the presence of K2CO3 in MeCN at 90°C for 60h afforded only imidazo[l,2-n]pyrimidine-3-carboxylates. 

Phosphoryl chloride converted imidazo[4,5-c]pyridin-4(5//)-one into the 4-chloro derivative (65JMC708), and there are other examples of hydroxy displacement in the [4,5-b] series (58AP368 70CHE1073). 

CN ( )-r-[3-(3-chloro-10,l I-dihydro-5//-dibenz[6/ azepin-5-yI)propyl]hexahydrospiro[imidazo[l,2-a]pyridine-3(2//),4 - piperidin]-2-one... 

Reaction of pyrido[ 1,2- pyrazin-4-one 304 with methyl cyanoacetate, cyanamide, and JI-oxo nitriles in AcOH at 70 °C gave imidazo[ l,2- ] pyridine 331, imidazo[l,2- ]-pyrimidine 332, and tetracyclic heterocycles 333, respectively <1996JHC639>. 

A rapid one-pot synthesis of imidazo-[l,2-a]-pyridines, pyrazines and pyrimidines was described in 1999 by Varma et al. [50], who used recyclable montmorillonite clay Kio under solvent-free conditions and microwave irradiation (Scheme 8.32). 

More recently, a new and straightforward one-pot approach was reported by Bu et al. <2003JOC5415>. This reaction involves the cyclocondensation of l,2-dipyridin-2-yl-ethane-l,2-dione 120 and arylaldehydes, in the presence of ammonium acetate. Imidazo[l,5- ]pyridines 121 were obtained in reasonable yields, but competitive formation of imidazoles 122 was observed. The amount of ammonium acetate used in this reaction was also shown to strongly influence the yield of the cyclization (Scheme 38). 

Some other ten rr-electron N-heterocycles, but with a nitrogen atom shared by two rings, also present two or more conjugated nitrogen protonation sites. One such system is imidazo[l,2-a] pyridine (1-azaindolizine, [98]), which may be viewed as an... 

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