2- Imino-6,7-dihydro-2//-pyrido

Heating the crystalline salt 2-aminopyridinium propiolate (346) at 100 °C in the solid state led to a 10 9 mixture of 2/f-pyrido[l,2-n]pyrimidin-2-one and ( )-3-(2-imino-l,2-dihydro-l-pyridyl)acrylic acid (347). Analysis of differental scanning calorimetry data shows unambiguously that the reaction takes place in the solid state. An endothermic peak at 81.1 °C corresponds to a solid state reaction, and a peak at 122-123 °C is attributed to melting. The product ratio of 2//-pyrido[l, 2-n]pyrimidin-2-one and 347 is 1 2.5 at 60°C, and 1 1.4 at 80°C (94MI12). 

Reaction of 2-cyanomethylpyridine with iV-(l-aryl-l-chloro-2,2,2-trifluoroethyl)-iV -(4-methylphenyl)carbodiimides, and with (1,1,2,2,2-pentachloro- and l,l-dichloro-2,2,2-trifluoroethyl)isocyanates or A-methoxycarbonyl-l,2,2,2-tetrachloro-, — l-chloro-2,2-trifluoroacetaldehyde imines afforded 3-aryl-4-cyano-l-(4-methylphenyl)imino-3-trifluoromethyl-2,3-dihydro-17/-pyrido[l,2-f]pyrimidines and 4-cyano-3-trichloro-, 4-cyano-3-trifluoro-17/-pyrido[l,2-4pyrimidin-l-ones, respectively <2004CHE47>. Refluxing 2-cyanomethylpyridine and iV-(l-aryl-l-chloro-2,2,2-trifluoroethyl)isocyanates in benzene furnished l-aryl-4-cyano-l-trifluoromethyl-l,2-dihydro-3//-pyrido[l,2-4pyrimidin-3-ones. However, when the solution of the isocyanate was added dropwise to the solution of 2-cyanomethylpyridine, and the reaction mixture was then treated with NEt at room temperature, the isomeric 3-aryl-4-cyano-3-trifluoromethyl-2,3-dihydro-l//-pyr-ido[l,2-dpyrimidin-l-ones were obtained. Reaction of l-(acetyl- and benzoylmethylene)-6,7-dimethoxy-l,2,3,4-tetra-hydroisoquinolines with PhCONCS yielded 1-acetyl-, 1 -benzoyl-9,10-dime thoxy-3-pheny 1-6,7-dihydro-2//-pyrimido[6,l- ]isoquinoline-2-thiones <2003SL2369>. 

Reaction of 9-benzyloxy-3,4-dihydro-277-pyrido[2,l- ][l,3]oxazinium mesylate with C5H9NH2 and BnNH2 occurred at position 9a, while with sterically hindered amines (e.g., Bu NH2, secondary amines), PhNH2 and NaN3 reacted at position 2 to give l-(3-hydroxypropyl)-2-(substituted imino)-3-benzyloxy-l,2-dihydropyridines and... 

Reaction of 2-cyanomethyl-4H-l,3-benzothiazin-4-one with benzoylace-tonitrile at 160°C yielded 8-cyano-7-imino-9-phenyl-7//,ll//-pyrido[2,l-6][l,3]benzothiazin-l 1-one (85MI1 86MI2). Reaction of 2-ethoxy-2,3 dihydro-4//-l,3-benzothiazin-4-one with 1,2,3,4-tetramethylbutadiene and 2,4-dimethyl-l,3-pentadiene in the presence of boron trifluoride in diethyl ether gave rise to 6,7,8,9-tetramethyl- and 7,9)9-trimethyl-5a,6,9,ll-tetrahydropyrido[2,l-6][l,3]benzothiazin-ll-one, respectively (73JHC149). 

Substituted-4-oxo-4//-pyrido[l,2-a]pyrimidines of type 74 (6-R H) are transformed to l,4-dihydro-4-oxo-l,8-naphthyridines on the action of heat.bl)-71-7l, 1 29 1 33 323 325 Ring transformation is facilitated by the nearly coplanar disposition of the 4-CO group and the 6-substituent of the pyrido-[l,2-u]pyrimidines. The steric interaction of these groups is shown by the relatively long C-4—N-5 bond (e.g., 147 pm for ethyl 6-methyl-4-oxo-4/f-pyrido[l,2-u]pyrimidine-3-carboxylate, as determined by X-ray study326). The strain caused by this interaction is relieved when the C-4—N-5 bond cleaves. Ring transformation probably takes place via the reactive imino-ketene intermediate (75).130... 

H-Purin 6-Imino-l-methyl-9-(l-propenyi)-l, 6-dihydro- E9b/2, 422 (1-Methylier.) Pyrido[2,3-c]pyridazin 4-Amino-7-... 

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