Imidazo pyridines 2,3-dihydro

Spinacine — see Imidazo[4,5-c]pyridine-6-carboxylic acid, 4,5,6,7-tetrahydro-Spiniferin-1, ( )-dihydro-occuiTence, 4, 705 synthesis, 4, 670 Spin-spin coupling constants pyridines, 2, 123 Spiramycin antibacterial veterinary use, I, 207 Spirans... 

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... 

CN l,2-dihydro-5-imidazo[l,2-a]pyridin-6-yi-6-methyl-2-oxo-3-pyridinecarbonitrile monohydrochloride... 

Numereous derivatives of benzimidazole, naphthoimidazoles and other condensed imidazole systems can be very effectively thiated with elemental sulfur on heating without solvent at 230-260°C. The product of this reaction is the corresponding imidazolin-2-thione formed in excellent yield (67ZOR1518, 95IZV2231). For example, imidazo[4,5-cjpyridines (329, R =H, Aik, Ar, C6H5CH2) gave 1,3-dihydro-2//-imidazo[4,5-c]pyridine-2-thiones (330). 

A selenium-assisted carbonylation reaction has been developed which gives 1,3-dihydro-2/f-imidazo[4,5-b]pyridin-2-ones (314) in an excellent yield (Scheme 30) <87BCJ1793>. Heating 2,3-diaminopyridine (312) with CO and an equimolar amount of selenium in the presence of N-methylpyrrolidine, proceeds through a selenolcarbonate intermediate (313) which then cyclizes to the desired product (314). 

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>. 

Furan 2-Aminomethyl-5-(2,4-dioxo-1,2,3,4-tetrahydro-pyrimidino)-2,5-dihydro- IV/lc, 578 Imidazo(l,2-a]pyridin 1,5-Dimethyl-8-nitro-7-oxo-l,2,3,7-tetrahydro-E15/3, 2790 [cycl. (R2N)2C = CH-N02 4- Diketen] 1,3-Oxazol 4-Cyan-5-(diethoxy-methylen-amino)- E4, 565 (Het — NH2 + Orthoester) Pyrazin 3-Amino-2-methoxycarbo-nyl-5-propanoyl- E9b/2, 324 (H - CO-R)... 

The pyrolysis of 3-azido-4-dialkylaminopyridines (424) and (427) by heating in nitrobenzene to generate nitrene intermediates (425) has also been used to form the imidazole ring of imidazo[4,5-c]pyridines (426) and (428) (66JCS(C)80). In one instance the intermediate dihydro compound (429) was trapped by carrying out the reaction in acetic anhydride (63JCS1666). 

Combinations of N- and 5-alkylation in 2-imidazoline-2-thiols can lead to 5,6-dihydro-4//-imidazo[2,l-6]thiazoles when the heterocycles are treated with ketones in the presence of a halo-genating agent. This is a variant of the Hantzsch thiazole synthesis <92SC1293>. A further example of A-acylation in combination with nucleophilic substitution is the conversion of 2-chloro-2-imi-dazoline into (131) when it is treated with pyridine and an aryl isocyanate <87JCS(P1)1033>. 2-Imidazolines like clonidine are also known to A-nitrosate <93JCS(P2)59l>. Intramolecular alkylation is exemplified in the base-induced rearrangement of 2,5-diaryl-4-chloromethyl-2-imidazolines (132) into pyrimidines (Scheme 64) <93JOC6354>. 

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