Pyridines reaction 4- phosphate esters

Very similar results are found for reactions of quinuclidines with phos-phorylated pyridine, which follow a Brpnsted slope of Pnuc = —0.1. The less reactive phosphorylated 4-morpholinopyridine follows a slope of (3nuc = -0.01 (12). The changes in (3nuc for these phosphorylated pyridines and phosphate esters with a poorer leaving group (lg) represent Hammond effects that are described by the cross-interaction coefficient, pxy, of equation 3. This cross coefficient is larger than the direct coefficient that describes... 

Mannitol hexanitrate is obtained by nitration of mannitol with mixed nitric and sulfuric acids. Similarly, nitration of sorbitol using mixed acid produces the hexanitrate when the reaction is conducted at 0—3°C and at —10 to —75°C, the main product is sorbitol pentanitrate (117). Xylitol, ribitol, and L-arabinitol are converted to the pentanitrates by fuming nitric acid and acetic anhydride (118). Phosphate esters of sugar alcohols are obtained by the action of phosphorus oxychloride (119) and by alcoholysis of organic phosphates (120). The 1,6-dibenzene sulfonate of D-mannitol is obtained by the action of benzene sulfonyl chloride in pyridine at 0°C (121). To obtain 1,6-dimethanesulfonyl-D-mannitol free from anhydrides and other by-products, after similar sulfonation with methane sulfonyl chloride and pyridine the remaining hydroxyl groups are acetylated with acetic anhydride and the insoluble acetyl derivative is separated, followed by deacetylation with hydrogen chloride in methanol (122). Alkyl sulfate esters of polyhydric alcohols result from the action of sulfur trioxide—trialkyl phosphates as in the reaction of sorbitol at 34—40°C with sulfur trioxide—triethyl phosphate to form sorbitol hexa(ethylsulfate) (123). 

Much of the pioneering work related to decontamination reactions in oil-in-water (o/w) microemulsions has been carried out by Mackay. He has studied, for example, the hydrolysis of phosphate esters (3, O, metallation of tetraphenylporphine (5 and alkylation of substituted pyridines (6 ). 

The Role of Nucleophile Solvation. The value of = 0 for the reaction of substituted pyridines with 2,4-dinitrophenyl phosphate (76) is puzzling. If the value of is a measure of the amount of the bond formation to the nucleophile in the transition state, this value might be taken to mean that there is no bond formation to the nucleophile in the transition state. This is obviously not the case, because there is a large increase in the rate of disappearance of the phosphate ester with increasing concentration of the nucleophile the reactions follow simple second-order kinetics. 

The mode of addition of hydrogenphosphonates to fluorinated ketones can also be complex. The addition of dialkyl, diphenyl or bis(trimethylsilyl) hydrogenphosphonates to methyl trifluoromethyl ketones occurs in the expected manner, but this contrasts with the behaviour of aryl perfluoralkyl ketones in the presence of triethylamine at room temperature, when the products, obtained even under such mild conditions, are phosphate esters (reaction 6), a situation which represents lack of stability of the hydroxyphospho-nate rather than novelty of the reaction under identical conditions, the corresponding alkyl aryl ketones fail to react. The same reaction with mixed-halogen ketones is still more involved, and the nature of the products depends on the reaction conditions if these are of a mild nature, and with catalysis by triethylamine or pyridine (depending on the particular ketone), the product is the expected (hydroxyalkyl)phosphonate 177, whereas with... 

Vitamin Bg exists as six separate forms in the pyridine group of water-soluble vitamins. The common forms are pyridoxal and pyri-doxamine together with their corresponding phosphate esters and pyridoxine forms. These compounds function as cofactors in a wide variety of enzyme reactions, but most notably in the transamination reaction of amino acid biosynthetic pathways. Extraction of this group of vitamins can be performed by the same methods as those described for the B2 vitamins (Section 11.8.3.3). 

A solution of 0.107 g carboxylic acid, 2-thioxo-2H-pyridin-l-yl ester (0.2 mmol), and 45.3 p.L t rt-butylthiol (0.4 mmol) in 4.0 mL allyl alcohol in a Pyrex flask was photolyzed at room temperature with a 250-W Philips krypton lamp for 1 h. After removal of the volatiles under vacuum, and P NMR spectra indicated a clean reaction and complete conversion of carboxylic acid, 2-thioxo-2H-pyridin-l-yl ester with essentially quantitative formation of diphenyl phosphate ( P NMR 8 -10.36 in CDCI3). Purification by preparative TLC (hexane/EtOAc = 20 1) gave 32.0 mg c/5/tra/is-2,2,4-trimethyl-3-phenyltetrahydrofuran as the major product, in a yield of 82%. 

Productive foldamer research requires foldamers with certain backbone characteristics. The backbone must be stable, easily synthesized and have some degree of flexibility. It is also helpful to have a well-characterized conformational profile, known intermolecular interactions (such as H-bonding), and good handling characteristics, such as solubility. As shown in Tables 44.1 and 44.2, a wide variety of bond forming reactions have been used to build foldamers. The most popular, by far, is the amide bond however, other chemistry highlights include ureas, phosphate esters, ethers, aryl ethynylenes, biphenyls, and pyridines. 

Protection of Phosphates and Phosphonates. 2-Hydroxy ethyl phenyl sulfone (1) has been used to differentially protect phosphate esters for nucleotide synthesis. Thus, reaction of the diphosphate (8) with 1 and l-(mesitylene-2-sulfonyl)-3-nitro 1,2,4-trIazole (MSNT) in pyridine afforded the differentially protected phosphate 9 in very good yield (eq 5). The 2-phenylsulfonylethyl phosphate can be cleaved under mild conditions by treatment with triethylamine. 

Deprotection of p-nitrophenethyl (NPE) phosphonate or phosphate esters is accomplished under basic, nonnucleophilic conditions by treatment with DBU in pyridine with formation of p-nitrostjrene. However, this method presents problems for sensitive substrates, since prolonged reaction times are required for deprotection to the dianion. The first elimination step proceeds... 

Chloromethyl-4-nitrophenol has been described as a protecting group for alkyl or aryl phosphates [10]. Upon treatment with pyridine, the group is activated to form a phos-phorylating agent, and dialkyl or alkyl aryl phosphate esters may be obtained on reaction with the appropriate alcohol or phenol (Fig. 6.4). 

The solvent system N2O4/DMF has been employed for the preparation of inorganic esters, e.g., phosphates and sulfates [221] as well as organic esters. The latter products were obtained by reacting the polymer with acyl chlorides, or acid anhydrides in the presence of a pyridine base. The nitrite ester formed has been successfully trans-esterified by the reaction with RCOCl... 

C. Reactions.—The iV-chloroquinonimine (50) reacts with monoalkyl phosphates in dry pyridine to give symmetrical pyrophosphate esters. If present in excess it can react further, giving an intermediate which is attacked by alcohols or water with cleavage of the pyrophosphate bond. 

Schrader prepared the ester (38) in 60% yield by reaction of sodium p-nitrophenate with diethyl chlorophosphate, using xylene as solvent for the reaction. He made it, but in lower yields, from p-nitrophenol and diethyl chlorophosphate, using, respectively, pyridine and sodium cyanide as acceptors for hydrogen chloride. Schrader also prepared it in 96% yield by nitrating diethyl phenyl phosphate at 0° C. or below. Under the conditions he used, Schrader claims that the nitro group is directed to the para position. No yield is given for the diethyl phenyl phosphate, which he presumably made from sodium phenate and diethyl chlorophosphate. Diethyl chlorophosphate may be prepared in high yield (30) from diethyl phosphite and chlorine. 

Loran and Williams, 1977. The reference intermolecular reaction is the attack of pyridine on methyl o-nitrophenyl phosphate (Kirby and Younas, 1970). Corrections for the conversion to a diaryl ester and a p-nitrophenyl leaving group are assumed to cancel out. Temperature correction uses E, = 14.8 kcal mol-1, as measured for the reference reaction 4 Lazarus et al., 1980... 

Nucleoside 5 -phosphorothioates have also been employed as activated nucleotide derivatives for synthesis of pyrophosphates.321 The interaction of tributylammonium 2, 3 -di-0-benzoyluridine 5 -phosphorothioate (73) with silver a-D-glucopyranosyl and a-D-galac-topyranosyl phosphates in pyridine solution, with subsequent de-benzoylation, gave the corresponding glycosyl esters in 60-70% yield. This procedure can probably be classified as a variant of the mixed-anhydride method, the driving force of the reaction being the formation of insoluble silver sulfide. 

A related method, of preparative value, was subsequently developed.323 It makes use of the 2-hydroxypyridyl esters (74), of nucleoside 5 -phosphates, which can readily be obtained from nucleoside 5 -phosphates and 2-pyridinol. The reaction of the derivative (74) with glycosyl phosphates in anhydrous pyridine gives rise to the... 

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