Diethyl 3-methyl-6-oxo-2/7,6/7-pyrido

Oxidation of diethyl 3-methyl-6-oxo-2//,6//-pyrido[2,l-Z)][l,3]thiazine-4,9-dicarboxylate and its 7,8-dihydro derivative with CF3CO3H in CH2CI2 at room temperature gave the respective sulfone in 73% and 38% yields, respectively (99JCS(P1)3569). Sulfoxide 91 or sulfone 92 of... 

Oxidation of 8-(l-methylethenyl)-2-oxo-7-thia-l-azabicyclo[4.3.0]octa-3,5-diene-5,8-dicarboxylate and its 3,4-dihydro derivative with peracids gave diethyl 3-methyl-6-oxo-2/7,6/7-pyrido[2,l- ][l,3]thiazine-4,9-dicarboxylate and its 7,8-dihy-dro derivative, respectively < 1999J(PI)3569>. Reaction of NH2(CH2)3NH2 with 5-O-methanesulfonyl-L-gulofuranose... 

Treatment of alkyl 9-benzyloxycarbonyl-3-methyl-6-oxo-2/7,6//-pyr-ido[2,l-f ][l,3]thiazine-4-carboxylates with BBr3 in CH2CI2 at -70 °C for 0.5-1 h and at room temperature for 3h yielded 9-carboxyl derivatives. The decarboxylation of these acids was unsuccessful. Hydrolysis of diethyl cA-3,4-H-3,4-dihydro-3-methyl-6-oxo-2//,6//-pyrido[2,l-f ][l,3]thiazine-4,9-dicarboxylate in aqueous EtOH with KOH at room temperature for 3 days yielded 4-ethoxycarbonyl-3,4-dihydro-3-methyl-6-oxo-2//,6//-pyrido-[2,l-f ] [1,3]thiazine-9-carboxylic acid (00JCS(P1)4373). Alkyl 9-hydroxy-methyl-3-methyl-6-oxo-3,4-dihydro-2//,6//-pyrido[2,l-f ][l,3]thiazine-4-car-boxylates were O-acylated with AC2O and (PhC0)20 in pyridine at room temperature for 12-48h. 

In 12 ml of acetic acid was dissolved 1.20 g of the resulting compound, and 25 ml of concentrated hydrochloric acid was added, followed by refluxing at 120-130°C for 90 min. Upon allowing the reaction mixture to stand at room temperature, colorless crystals were precipitated, which were collected by filtration and washed successively with a small amount of water, ethanol and diethyl ether to obtain 0.96 g of (-)-9,10-difluoro-3-methyl-7-oxo-2,3-dihydro-7H-pyrido[l,2,3-de][l,4]benzoxazine-6-carboxylic acid. 

Diethyl t7r-3//,4//-3-mcthyl-6-oxo-3,4-di hydro-2//,6//-pyrido[ 2,1 - [ 1,3]-thiazincM,9-dicarboxylatc was obtained from the 3-methyl-6-oxoH//,6// derivative by catalytic hydrogenation over 5% Rh on alumina and from the... 

Reactions of 2-aminopyridines and diethyl 2-aryl-4-hydroxy-4-methyl-6-oxocyclohexane-l,3-dicarboxylate (309) in acetic acid for 4 h gave either ethyl 1,2-dihydro-l 1-oxo-l l//-pyrido[2,l -6]quinazoIine-2-carboxylates (310) or their isomeric ethyl 7,8-dihydro-6-oxo-6//-pyrido[l,2-a]quinazoline-8-carboxylates (311) (92PHA336). 

The cyclocondensation of 2-amino-6-methylpyridine and diethyl 3-oxo-pimelate did not occur at room temperature by standing over concentrated sulfuric acid instead, it gave ethyl 4-(6-methyl-4-oxo-4//-pyrido[ 1,2-a] pyrimidin-2-yl)butanoate by heating in polyphosphoric acid in 25% yield (87SC319). 

The amino moiety of the 3-carbohydrazide group of unsaturated and 6,7,8,9-tetrahydro-4-oxo-47/-pyrido[l,2-n]pyrimidine-3-carbohydrazides was condensed with acetone and 5-nitro-2-furoaldehyde (830MR687 88EUP252809). The reaction of 6-methyl-6,7,8,9-tetrahydro-4-oxo-4//-pyrido[l,2-a]pyrimidine-3-carbohydrazide with diethyl 2-[2-dimethyl-amino)vinyl]-6-methylpyridine-3,5-dicarboxylate in boiling ethanol for 4 hours afforded N-( 1,6-naphthyridin-6-yl)-4-oxo-4//-pyrido[ 1,2-a]pyrimi-dine-3-carboxamide 426 (85MIP1). 

To 1.13 g of (-)-7,8-difluoro-2,3-dihydro-3-methyl-4H-[l,4]benzoxazine was added 1.58 g of diethyl ethoxymethylenemalonate, and the mixture was stirred at 130-140°C for 70 min. The reaction mixture was subjected to column chromatography using 50 g of silica gel and eluted with chloroform to obtain 2.47 g of diethyl [(-)-7,8-difluoro-3-methyl-2,3-dihydro-4H-[l,4] benzoxazin-4-yl]methylenemalonate. This product was dissolved in 5 ml of acetic anhydride, and 10 ml of a mixture of acetic anhydride and concentrated sulfuric acid (2/1 by volume) with stirring under ice-cooling, followed by stirring at 50-60°C for 40 min. To the reaction mixture were added ice and an aqueous solution of sodium bicarbonate, and the product was extracted three times with 150 ml portions of chloroform. The combined extract was washed with water, dried over anhydrous sodium sulfate and concentrated. The precipitate was washed with a small amount of diethyl ether to yield 1.32 g of (-)-ethyl 9,10-difluoro-3-methyl-7-oxo-2,3-dihydro-7H-pyrido[l,2,3-de][l,4] benzoxazine-6-carboxylate. 

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