Pyridines pyrido pyrimidinium

Theoretical calculations (B3LYP/6-31G ) indicated that in their NMR spectra C(2) and C(9) carbons of n /2ydro-(2-hydroxy-4-oxo-4//-pyrido[l,2-n]pyrimidinium)hydroxide mesoionic forms appeared at significantly higher field (ca. 159-160 ppm and 115-116 ppm, respectively), than in the 2-hydroxy-4//-pyrido[l,2-n]pyrimidin-4-one tautomers (ca. 169-173 ppm and 130 ppm, respectively) (00JCS(P2)2096). C(8) carbon of mesoions (pyridine-y type carbon) appeared at lower field (144-146 ppm) than 6-C (140 ppm, pyridine-o type carbon), as is typical of pyridinium compounds. 

Whereas in all previously mentioned inverse cycloaddition reactions [h]-fused pyrido annelated systems are formed, some reactions are described which lead to [c]-pyridine annelated bicyclic systems. 5-(Butynylthio)pyrimidines (R = Ph, NHCOCH3) give on heating at 180°C in nitrobenzene 5-R-2,3-dihydrothieno[2,3-c]pyridines (89T803). 5-Propynyloxymethylpyrimidines also readily undergo cycloaddition into l,3-dihydrofuro[3,4-c]pyridines (89T5151) (Scheme 39). Considerable rate enhancements were observed with quaternized pyrimidinium salts. Whereas... 

According to Chuiguk and Oksanich13 the reaction of 2-aminopyridinium perchlorates and /i-chlorovinylaldehydes led exclusively to the 4-substituted products (9) whereas from 2-amino-6-methylpyridine no cyclic product was obtained. With //-chlorovinyl ketones both the 2- and 4-substituted pyrido-[l,2-u]pyrimidinium salts were detected by H NMR.3 2-Amino-6-methyl-pyridine gave rise only to the 2-substituted isomer (10). 

By the reaction of 2-(alkylamino or benzylamino)pyridines with epichlorohydrin or l,3-dichloro-2-propanol, quaternary pyrido[l,2-a]pyrimidinium salts (132) were obtained.188... 

As shown recently , refluxing 6-methyl-substituted 3-azapyrylium perchlorates 377 in DMF/AcjO mixture gives the pyrido[l,2-c]pyrimidinium salts 379, while when carrying out this reaction at 20 C it gives the -acylaminovinyl pyridines 380. The authors assume that formation of anhydro base 378 takes place initially, and then 378 reacts with another molecule of 377 . The same products 379 and 3 were isolated from the condensation of 6-methylene-1,3-oxazines 378 with 3-azapyrylium salts 377 prepared beforehand (equation 108). The structure of 379 (R = Et) was established by X-ray crystallography. 

---