2- Imino-2//-pyrido pyrimidine hydrochloride

The reaction of 2-aminopyridine hydrochlorides and allenic nitriles either neat at 90°C for 20 hours or in boiling methylene chloride for 15 hours afforded unstable 2-imino-2//-pyrido[l,2-a]pyrimidine hydrochlorides 71, which could be isolated as hydrates in about 50% yield [88JCS(P1)975]. If the reactions were carried out in boiling 95% ethanol for 72 hours, the initially formed 2-imino-2//-pyrido[ 1,2-a Ipyrimidines 71 were hydrolyzed and 2-pyridyl ketones 73 could be isolated. Under the latter conditions 3-hydroxy-2-aminopyridine gave 2-iminopyridopyrimidines 74, which were stabilized by the formation of zwitterionic structures (Scheme 5). [Earlier the ring-opened products 73 (R = H, 3-NH2) were described as a 4-imino-4/7-pyrido[ 1,2-a]pyrimidine derivative 72 (81TL4127)]. 

The treatment of 2-imino-4-alkyl-2//-pyrido[l,2-a]pyrimidine hydrochlorides 288 with sodium carbonate in 95% ethanol at room temperature for 10 hours gave 4-hydroxyl-4-alkyl derivatives 289 as hydrates [88JCS(P1)975]. If the reaction mixtures were refluxed for 24 hours, then ring-opened products 290 were isolated. The presence of a hydroxyl group at position 9 increased the stability of bicyclic 289. 

Okamoto et al. prepared the pyrido[l,2-c<]pyrimidines (142 R = H, Me) by heating 2-aminopyridines with ethyl 3-chloropropionimidate hydrochloride in ethanol or acetonitrile. In the case of 2-aminopyridine and 2-amino-4-methylpyridine, not only 142 (R = H, 8-Me) but also the 2-imino derivatives were isolated, which on treatment with acid were transformed to 2-oxopyrido[l,2-c<] pyrimidines (142). With 2-amino-6-methylpyridine or... 

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