Ethyl 2-chloro-6-methyl-4//-pyrido

Bromo atom of ethyl (3S)-10-bromo-3-methyl-7-oxo-2,3-dihydro-7//-pyrido[l,2,3- fe]-l,4-benzothiazine-6-carboxylate was change for hetaryl groups with tributylstannyl derivatives of heterocycles in the presence of (Ph3P)2Pd(II)Cl2 in boiling toluene (OOMIPIO). 7-Aryl-5-oxo-2,3-dihydro-5//-pyrido[l,2,3- fe]-l,4-benzothiazine-6-carboxylates, 6-carboxamides and their 1,1-dioxide derivatives were prepared from 7-chloro derivatives in the... 

Aminopyridine and its 3-hydroxy and 6-methyl derivatives were reacted with ethyl 2-chloro- and 2-phenoxyacetoacetates by heating in a mixture of phosphoryl chloride-polyphosphoric acid to give the appropriate 3-substituted 2-methyl-4//-pyrido[l,2-a]pyrimidin-4-ones (83H1083). 

Chloro derivative 291 was obtained from dioxo derivative 70 by treatment of phosphoryl chloride in dimethylformamide at 100°C for 2 hours (80CPB3537). The treatment of chloro derivative 291 with methylhydra-zine in a mixture of ethanol and chloroform under reflux gave 2H-pyrido[ 1,2-a]pyrimidin-2-one 295 and rearranged pyridazino[3,4-6]-quinoxaline 296 in 4.8% and 78% yields, respectively (Scheme 21) (80CPB3537). 3,4-Dihydroquinoxalinone 70 could not be rearranged into pyridazino[3,4-6]quinoxaline 296 by treatment with methylhydrazine. When hydrazine hydrate was employed instead of methylhydrazine, tricyclic ethyl ester 297 (R1 = Et) was obtained. The latter reaction gave methyl ester 297 (R1 = Me) when carried out in a mixture of methanol and chloroform (80CPB3537). 

When ethyl 2-chloro-6-methyl-47/-pyrido[l, 2-a]pyrimidine-3-acrylate... 

Cyclization of ethyl lV-(2-pyridyl)-2-methyl)- and VV-(5-chloro-2-pyridyl)-malonamates in a mixture of POCl3 and PPA at 130 °C gave 2-chloro-3-methyl- and 2,7-dichloro-4f/-pyrido[l,2-a]pyrimidin-4-ones in 26 and 61% yields, respectively (00BMC751). 

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