Pyridine-3-carboxylates, 4-hydroxy

The methods outlined, of course, are readily applicable to a wide variety of substituted heterocycles like the carboxyl, hydroxy and mercapto derivatives of pyridines, pyridine 1-oxides, pyrroles, etc. The application to amines and to diaza compounds such as pyrimidine, where the two centers are basic, is obvious except that now 23 takes the role of the neutral compound, 21 and 22 the roles of the tautomeric first conjugate bases, and 20 the role of the second conjugate base. Extensions to molecules with more than two acidic or basic centers, such as aminonicotinic acid, pyrimidinecarboxylic acids, etc., are obvious although they tend to become algebraically cumbersome, involving (for three centers) three measurable Kg s, four Ay s, and fifteen ideal dissociation constants (A ), a total of twenty-two constants of which seven are independent. 

Chemical Name 3-Pyridine carboxylic acid compounded with 3,7-dihydro-7-[2-hydroxy-3-[(2-hydroxymethyl)methylamino] propyl] -1,3-dimethyl-1 H-purlne-2,6-dlone(1 1)... 

Copper(ii) complexes of 8-amino-7-hydroxy-4-methylcoumarin, 1,10-phenanthroline-2-carboxamide, 2-pyridone, 2,3-di-(2-pyridine N-oxide)-quinoxaline," pyridine carboxylates, l-(2 -pyridyl)-2-azonaphthol, and l-(2 -benzothiazolyl)-2-azonaphthol have also been reported. 

Ethyl 5-cyano-2-(a-cyanoethoxycarbonylmethyl)-4-oxo-l,4-dihydro-3-pyridine-carboxylate (42) gave ethyl 3-cyano-7-hydroxy-4,5-dioxo-1,4,5,6-tetrahydro-l,6-naphthyridine-8-carboxylate (43) (Et3N, EtOH, reflux, 3 h 65%).698... 

Nicotinic acid (3-pyridine carboxylic acid or niacin) nicotinamide (nicotinic acid amide), niacinamide, 3-pyridine-carboxylic acid amide Thiamines, hydroxy-ethylthiamine... 

The conclusions to be reached from these data are, chiefly, that whilst hydroxy-and mercaptopyridines and pyridine carboxylic acids exist predominantly in the Z forms (i.e. as pyridones, pyridthiones and zwitterions), aminopyridines prefer the NM forms (that is, they are mainly amines and not iminesj. The spectroscopic evidence supporting these conclusions has already been discussed, and this tautomerism is further discussed below. 

The reduction of pyridine-carboxylic acids has been mentioned already (pp. 258, 263), and it has been seen that electrolytic reduction or reduction with zinc and acetic acid can give methyl- or hydroxymethylpyridines. Whilst the electrolytic reduction of benzoic acid to benzyl alcohol is well known, benzene-carboxylic acids are generally not so readily reduced as the pyridine-carboxylic acids. Two other additional cases might be quoted. A dichloropyridine-carboxylic acid has been reduced by phosphorus and hydriodic acid to a dichloromethylpyridine , and 2,6-dichloropyridine-4-carboxylic acid with zinc and acetic acid gives 2,6-dichloro-4-hydroxy-methylpyridine . Isonicotinic acid is reduced to the alcohol by tin and hydrochloric acid . 

In peptide syntheses, where partial racemization of the chiral a-carbon centers is a serious problem, the application of 1-hydroxy-1 H-benzotriazole ( HBT") and DCC has been very successful in increasing yields and decreasing racemization (W. Kdnig, 1970 G.C. Windridge, 1971 H.R. Bosshard, 1973), l-(Acyloxy)-lif-benzotriazoles or l-acyl-17f-benzo-triazole 3-oxides are formed as reactive intermediates. If carboxylic or phosphoric esters are to be formed from the acids and alcohols using DCC, 4-(pyrrolidin-l -yl)pyridine ( PPY A. Hassner, 1978 K.M. Patel, 1979) and HBT are efficient catalysts even with tert-alkyl, choles-teryl, aryl, and other unreactive alcohols as well as with highly bulky or labile acids. 

Ethers of benzenepentol have been obtained by Dakin oxidation of the appropriately substituted acetophenone. Thus, the oxidation of 2-hydroxy-3,4,6-ttimethoxyacetophenone and 2-hydroxy-3,4,5-ttimethoxyacetophenone with hydrogen peroxide ia the presence of alkali gives l,2-dihydroxy-3,4,6-ttimethoxybenzene and l,2-dihydroxy-3,4,5-ttimethoxybenzene, respectively further methylation of these ethers yields the pentamethyl ether of benzenepentol (mp 58—59 degC) (253). The one-step aromatization of myoinositol to produce esters of pentahydroxybenzene is achieved by treatment with carboxylic acid anhydrides ia DMSO and ia the presence of pyridine (254) (see Vitamins). 6-Alkyl- or... 

Selenolo[2,3-b]pyridine-2-carboxylic acid, 3-hydroxy-synthesis, 4, 1034 Selenolopyridines, 4, 1034—1036 H NMR, 4, 1035, 1036 Selenolo[2,3-c]pyridines synthesis, 4, 1035 Selenolo[3,2-b]pyridines deuteriodeprotonation, 4, 1035 synthesis, 4, 1034 Selenolo[3,2-c]pyridines synthesis, 4, 1035 Selenolo[2,3-b]pyrroles ionization potentials, 4, 1046 Selenolo[3,2-b]pyrroles ionization potentials, 4, 1046 Selenolo[3,4-c]pyrroles non-classical... 

P-Acetoxy-5-hydroxy-B-mrcholestan-6-carboxylic Acid 5,6-Lactone (TO)."" A solution of 5 g (0.011 mole) of keto acid (69), 4.4 g of benzoyl chloride and 10 ml of anhydrous pyridine is allowed to stand for 3 days at room temperature. After a short period the mixture turns red-brown and at the end of the reaction the dark semi-solid mass is poured into 200 ml of water and extracted with two 100 ml portions of ether. The ethereal extracts are washed twice with equal portions of 5 % sodium hydroxide and water, dried and the ether evaporated. The red sirupy residue is mixed with 10 ml of methanol and a brown solid separates immediately. After standing for 1 hr the solid is removed by filtration and washed with methanol. A second crop is obtained upon concentration of the filtrate. The combined crops are recrystallized twice from methanol to give (70) as white needles mp 124-125° yield 2.8 g (58 %). 

Jaffe to pyridine-3- and -4-carboxylic acids and to 3-hydroxy-pyridine for which values of the a constants are much more certain. 

Alkyl-1,4-dihydropyridines on reaction with peracids undergo either extensive decomposition or biomimetic oxidation to A-alkylpyridinum salts (98JOC10001). However, A-methoxycarbonyl derivatives of 1,4- and 1,2-dihydro-pyridines (74) and (8a) react with m-CPBA to give the methyl tmns-2- 2>-chlorobenzoyloxy)-3-hydroxy-1,2,3,4-tetrahydropyridine-l-carboxylate (75) and methyl rran.s-2-(3-chlorobenzoyloxy)-3-hydroxy-l,2,3,6-tetrahydropyridine-l-carboxylate (76) in 65% and 66% yield, respectively (nonbiomimetic oxidation). The reaction is related to the interaction of peracids with enol ethers and involves the initial formation of an aminoepoxide, which is opened in situ by m-chlorobenzoic acid regio- and stereoselectively (57JA3234, 93JA7593). 

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. 

Ketones and carboxylic esters can be a hydroxylated by treatment of their enolate forms (prepared by adding the ketone or ester to LDA) with a molybdenum peroxide reagent (MoOs-pyridine-HMPA) in THF-hexane at -70°C. The enolate forms of amides and estersand the enamine derivatives of ketones can similarly be converted to their a hydroxy derivatives by reaction with molecular oxygen. The M0O5 method can also be applied to certain nitriles. Ketones have also been Qc hydroxylated by treating the corresponding silyl enol ethers with /n-chloroperoxy-... 

A more general route to 4-acetoxy-l,3-dioxanes utilizes the reductive acylation of l,3-dioxane-4-ones [46] (Scheme 21). l,3-Dioxane-4-ones 126 are prepared from the corresponding -hydroxy carboxylic acids. Low temperature reduction with DIBALH generates a diisobutylaluminum hemiacetal (127) which undergoes acylation in situ with AC2O in the presence of pyridine and DMAP. This method allows for the preparation of a wide range of 4-acetoxy-l,3-dioxanes, without the problem of a-epimerization. This method also represents a general approach to acylic a-acetoxy ethers, which are themselves useful synthetic intermediates [47,48]. 

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