2-substituted pyrimidine-5-carboxylic esters

Enolates can also function as masked aldehydes or ketones and a new synthesis of 2-substituted pyrimidine-5-carboxylic esters 652 used a doubly masked dialdehyde 651, where one aldehyde was protected as an acetal and the other was used in the form of its sodium enolate <2002S720>. 

A method for the synthesis of 2-substituted pyrimidine-5-carboxylic esters is described based on the similar concept of condensation of amidine... 

The other main reaction in this class is the Dieckmann-type cyclization of the intermediates (163) from 4(6)-halo-5-ethoxycarbonylpyrimidines with AC-substituted /3-alanine esters and nitriles, and related compounds, to give 5,6,7,8-tetrahydro-5-oxopyrido[2,3-[Pg.221]

Although hydrazines often behave as difunctional reagents, they react with an isothiocyanato-carboxylate ester at room temperature at one nitrogen only. Amines and amino acids yield 3-substituted pyrimidines on being heated with this isothiocyanate (review of isothiocyanates [3990]). 

The replacement of the 4-chloro substituent by reaction with TV-substituted /1-alanine esters and the subsequent Dieckmann cyclization yields alkyl 5-oxo-5,8-dihydropyrido[2,3-J]pyrimidine-6-carboxylates.15 3 -157... 

The cyclization of educts with a C-C-C—N pyrimidine structure is similar to the second step of the Gould-Jacobs reaction.194 The reaction of an appropriately substituted pyrimidin-4-amine with diethyl (ethoxymethylene)malonate affords the requisite diethyl [(pyrimidinyl-amino)methylene]malonate. The thermal cyclization of this intermediate, an acylation of the pyrimidine nucleus by one of the ester functions to give ethyl 5-oxopyrido[2,3-t/]pyrimidine-6-carboxylate 1, is effected by heating to 250-320 °C, preferably in mineral oil,195 Dowtherm,196 or diphenyl ether.197 201... 

K.S. Atwal, G.C. Rovnyak, S.D. Kimball, D.M. Floyd, S. Moreland, B.N. Swanson, J.Z. Gougoutas, J. Schwartz, K.M. SmiUie, M.F. Malley, Dihydropyrimidine calcium channel blockers. 11. 3-Substituted-4-aryl-l,4-dihydro-6-methyl-5-pyrimidine carboxylic acid esters as potent mimics of dihydropyridines, J. Med. Chem. 33 (1990) 2629-2635. 

The A-substituted derivatives of 4-oxo-4//-pyrido[l,2-n]pyrimidine-3-carboxamides and -3-acetamides and l,6-dimethyl-4-oxo-1,6,7,8-tetrahy-dro-4//-pyrido[l,2-n]pyrimidine-3-carboxamide were prepared by treatment of the appropriate 3-carboxylic acids and acetic acid, first with an alkyl chloroformate in the presence ofNEt3 in CHCI3 below — 10°C, then with an amine (98ACH515). A-Phenethyl and A-[2-(3,4-dimethoxyphenyl)ethyl] derivatives of 6-methyl-6,7,8,9-tetrahydro-4//-pyrido[l, 2-n]pyrimidine-3-acetamide were obtained in the reaction of 6-methyl-6,7,8,9-tetrahydro-4//-pyrido[l,2-n]pyrimidine-3-acetic acid and phenethylamines in boiling xylene under a H2O separator. Hydrazides of 4-oxo-4//- and 4-oxo-6,7,8,9-tetrahydro-4//-pyrido[l, 2-n]pyrimidine-3-acetic acid were prepared from the appropriate ester with H2NNH2 H2O in EtOH. Heating 4-oxo-4//- and 6-methyl-4-oxo-6,7,8,9-tetrahydro-4//-pyrido[l, 2-n]pyrimidine-3-acetic hydrazides in EtOH in the presence of excess Raney Ni afforded fhe appropriafe 4-oxo-6,7,8,9-fefrahydro-4//-pyrido[l,2-n]pyrimidine-3-acefa-mide. In the case of the 4-oxo-4// derivative, in addition to N-N bond... 

Hydroxy-L-prolin is converted into a 2-methoxypyrrolidine. This can be used as a valuable chiral building block to prepare optically active 2-substituted pyrrolidines (2-allyl, 2-cyano, 2-phosphono) with different nucleophiles and employing TiQ as Lewis acid (Eq. 21) [286]. Using these latent A -acylimmonium cations (Eq. 22) [287] (Table 9, No. 31), 2-(pyrimidin-l-yl)-2-amino acids [288], and 5-fluorouracil derivatives [289] have been prepared. For the synthesis of p-lactams a 4-acetoxyazetidinone, prepared by non-Kolbe electrolysis of the corresponding 4-carboxy derivative (Eq. 23) [290], proved to be a valuable intermediate. 0-Benzoylated a-hydroxyacetic acids are decarboxylated in methanol to mixed acylals [291]. By reaction of the intermediate cation, with the carboxylic acid used as precursor, esters are obtained in acetonitrile (Eq. 24) [292] and surprisingly also in methanol as solvent (Table 9, No. 32). Hydroxy compounds are formed by decarboxylation in water or in dimethyl sulfoxide (Table 9, Nos. 34, 35). 

The carboxyl group of 2-[4-(4-carboxybenzoyl)benzyloxy]-3-methyM77-pyrido[l,2- ]pyrimidin-4-one, prepared by hydrolysis of the methyl ester, was reacted first with (Et02C)20 in DMF at room temperature and then with 4-phenylpiperazine and 4-piperidinopiperidine to give the appropriate amide derivatives <1996EPP733633>. The N-substituted derivatives of 4-oxo-477-pyrido[l,2-tf]pyrimidine-3-carboxamides and -3-acetamides and 1,6-dimethyl-4-oxo-l,6,7,8-tetrahydro-477-pyrido[l,2-tf]pyrimidine-3-carboxamide were prepared by treatment of the appropriate... 

The reactions of the esters of 5-aminoisoxazole-4-carboxylic acids with acetic anhydride and aryl isocyanates yield substituted isoxazolo[5,4-J]pyrimidines 50 and 51 (86ACS(B)760, 86JHC1535) (Scheme 22). 

Substituted 4-chloropyrimidine-5-carboxylic acid esters react with 3-(alkylamino)- or 3-(aryl-amino)propanoic acid esters to give diesters suitable for Dieckmann cyclization. The resulting dihydropyrido[2,3-r/]pyrimidines are then oxidized to the corresponding pyrido[2,3-<7]-pyrimidin-5(8//)-oncs 17. 53-157... 

Many carboxy derivatives are available by primary syntheses. Otherwise the best route to simple pyrimidinecarboxylic acid derivatives is oxidative. This statement is even more applicable to our present situation with readily available acyl-, alkenyl-, or alkynylpyrimidine substrates from the coupling procedures, which serve as excellent substrates for oxidative reactions. The normal carboxylic acid reactions are observed ester formation, ester hydrolysis, aminolysis, acid chloride formation and reactions. A carboxy group in an electrophilic position may readily be lost when the pyrimidine ring is further depleted of 7t-electrons by its substitution pattern selective decarboxylation can be effected in pyrimidinedicarboxylic acids. 

Geometrical trans to cis isomerization of 3,3 -, 4,4 -, and 5,5 -disubstituted 2,2 -diphenoquinones has been studied by computational methods.The double bond isomerization of butene-catalysed l-ethyl-3-methyl-imidazolium chloride ionic liquid has been similarly examined and stepwise isomerization is suggested.The reaction of l,2-di(l-adamantyl)-2-thioxoethanone with diazomethane and 2-diazopropane gave 2-acylthiiranes via 2 - - 3-cycloaddition, elimination of nitrogen, and 1,3-dipolar electrocyclization of the intermediate acyl-substituted thiocarbonyl ylides. Rearrangement of pyrimidine-5-carboxylic acids esters to 5-acylpyrimidones does not occur in the examples studied and a [l,4]-phospho-Fries rearrangement has been reported. ... 

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