2-Substituted-1,2-dihydro-4//-pyrido

Heating diethyl (2-pyridylamino)methylenemalonates 304 (R = COOEt, = Me, OH) in AcOH afforded 4-oxo-4//-pyrido[l, 2-n]pyrimidine-3-carboxylates 305 (R = Me, OH) (96JHC1041). Flash vacuum thermolysis of 2-substituted 3-(2-pyridylamino)acrylates 304 (R = CN, COOEt, R = H) through a packed silica tube (530 °C, 0.01 mmHg) gave 3-substituted 4//-pyrido[l,2-n]pyrimidm-4-ones 306 (R = CN, COOEt) (94AJC1263). Ethyl 7-methyl-4-oxo-l, 4-dihydro-1,8-naphthyridine-3-carboxylate (79%) was... 

When pyridinium A -imine salts 157 were reacted with methylphenyl-cyclopropenone (158, R = Ph, R = Me) in the presence of a base, dihydro-pyrido[l,2-h]pyridazin-3-ones (159) were formed, which subsequently underwent oxidation to produce 3//-pyrido[l,2-h]pyridazin-3-ones (160) under the reaction conditions [76JCS(CC)275 78JOC2892], In some cases the dihydro intermediates (159) could be isolated. 3-Substituted derivatives (157, R = 3-Me, 3-CN R = H) gave mixtures of isomers of 160 (R = 5-... 

Ring transformation of the initial 6-substituted 4//-pyrido[l,2-a] pyrimidin-4-ones also occurred when 2-[(6-substituted 2-pyridyl)acrylates were heated in a high-boiling solvent. For example, heating diethyl [(4,6-dimethyl-2-pyridyl)amino]malonate in boiling diphenyl ether afforded ethyl 5,7-dimethyl-4-oxo-1,4-dihydro-1,8-naphthyridine-3-carboxylate... 

The treatment of 8//-pyrido[l,2-a]quinoxalin-8-ones with a Grignard reagent gave 6-substituted 5,6-dihydro derivatives, which could be dehydrogenated to 6-substituted 8//-pyrido[l,2-a]quinoxalin-8-ones (35CB 1716). 

For a structure-activity relationship study on 5//-pyrido[4,3-(j]indoles (y-carbolines), we needed both 1-unsubstituted 271 and 1-substituted methyl 2,3-dihydro-3-oxo-5//-pyrido[4,3-(j]indole-4-carboxylates 272 (Scheme 42). 

Thus, novel 2-substituted methyl 2,3-dihydro-l-methyl-3-oxo-5//-pyrido[4,3-/j] indole-4-carboxylates are available. Since the methyl group at the 1 position is expected to react with various reagents, many 1-substituted derivatives could be produced. 

Irradiation of 9-substituted 6-oxo-3,4-dihydro-2//,6//-pyrido[l,2-Z)]-[1,3]thiazine-4-carboxylate 93 in benzene afforded tricyclic derivatives 94, sometimes as a diastereomeric mixture (00JCS(P1)4373). 

Characteristic H NMR data of (4a/ ,55)- and (4n5,5R)-2-substituted 5- [A-(/e/ /-butoxycarbonyl)-L-tryptophyl]amino perhydropyrido[l,2-c]pyri-midine-l,3-diones were tabulated (01JMC2219). C CPMASS NMR data of 4-(4-methoxyphenyl)perhydropyrido[l,2-c]pyrimidine were reported (00JST73). C NMR data were reported for eight 4-aryl-2,3,5,6,7,8-hexahydro-l//-pyrido[l,2-c]pyrimidin-l,3-diones in the solid state and in CDCI3 solution (00JPO213). The structure of 4-aryl-3,4-dihydro-2//-pyrido [l,2-c]pyrimidine-l,3-diones and their 2,3,5,6,7,8-hexahydro derivatives were characterized by H and C NMR data (99JHC389). Conformational analysis of 6-methyl-2,3,4,6,7,ll/)-hexahydro-l//-pyrimido[6,l-n]isoquino-lin-2-ones 138 and 139 were carried out by H and C NMR studies (97LA1165). 

The respective amide was prepared from 7-substituted 5-oxo-2,3-dihydro-5//-pyrido[l,2,3-de]-l,4-benzoxazine-6-carboxylic acids via acid chlorides with different benzylamines (00M1P3). 6-Carboxamides were N-benzylated, and a side-chain phenolic hydroxy group was O-alkylated. 7-Aryl-5-oxo-2,3-dihydro-5//-pyrido[l, 2,3-r/e]-1,4-benzoxazine-6-carboxylic acid was obtained from the ethyl ester by alkalic hydrolysis. 

Oxo-2,3,6,7-tetrahydro-5//-pyrido[l,2,3- /e]-l,4-benzoxazine-2-carbox-ylates (291, X = H2) were obtained by hydrogenation of 4-substituted 3, 4-dihydro-2//-1,4-benzoxazine-2-carboxylates (290, X = H2) over 10% Pd/C catalyst, then by the treatment of free acids with (CF3C0)20 (99EUP894796). 5,7-Dioxo-2,3,6,7-tetrahydro derivatives 291 (X = 0) were prepared similarly from 290 (X = O). The products 291 (X = O) exist in 7-hydroxy-5-oxo-2,3-dihydro-5// tautomeric form. 

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... 

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