Pyridine esters using

Esters attached to the pyridine were used as precursors of amides <2003TL1675> and aldehydes on the pyridine ring underwent Horner-Emmons conversion to acrylates <1995JHC787>. 

If the heterocyclic base contains several pyridine-type nitrogens select can also be observed. Indeno[l,2-b]quinoxalines, for example, are quaternized at the N-10 atom.110 The alkylation of heterocycles conta one pyrrole-type nitrogen and several pyridine-type nitrogens is appar selective (e.g., indolo[2,3-b]quinoxaline).201 The yields of quaternary however, are extremely low,201 even if phenacyl halides or a-halo ester used.207 Perhaps the resultant quaternary salts are dealkylated.200,207... 

The reactions of the other sulfinyl chlorides (n-Pr, z -Pr, p-Tol) with DAG using z -Pr2NEt as base led to the formation of (S)-sulfinate esters as the major isomers with high selectivity (89 to >95%) instead of (/ -)sulfinate esters predominantly obtained when pyridine was used as base (70 to > 95% de, Table 20). 

The synthesis of the oxazole compound 45 starts with the coupling of the N-protected (/ )-methylcysteine compound 18 with threonine terf-butyl ester using bis(2-oxo-3-oxazolidi-nyl)phosphinyl chloride (BOP-Cl) [15] as a coupling reagent. Jones oxidation of the threonine hydroxy group leads to the ketoamide 44. The desired oxazole ring is closed by treatment with thionylchloride/pyridine. After deprotection, the oxazole, compound 45 is obtained. In the next step the oxazole compound 45 is coupled with the tris(thiazoline) compound 43 to yield the thioester 46. Now Fukuyama closes the fourth and last thiazoline ring (46 47). After conversion of the carboxylic acid function into a methyl-... 

Ethers, Esters, and Carboxylic Acids.— Monosulphates of partially formylated bile acids were prepared using SOs-EtsN complex in pyridine. Esters of testosterone and 19-norethisterone and hindered carboxylic acids were conveniently prepared by adding the alcohols in pyridine to a solution of the... 

Ortho esters may be brominated in pyridine solution. The reaction takes place rapidly at 10-30° to give good yields of a-bromoortho esters. Higher yields are obtained when a mixture of carbon tetrachloride and pyridine is used as solvent. The reaction fails for ethyl orthoisobutyrate. Two a-hydrogen atoms of ethyl orthoacetate have been replaced by bromine atoms to give ethyl orthodibromoacetate (53%). ... 

The occasional preliminary purification of products by aqueous washes usually coincides with the use of pyridine or dimethylformamide as solvent. Esters such as succinimido and benzotriazolyl are often prepared in situ, meaning that they are not isolated but subjected to aminolysis immediately after the esterification reaction.P " Slight decomposition can accompany the esterification of Boc amino acids, in particular if dichloromethane is used as solvent and the acidic EDC is used as reagent.P l Publications with a major focus on the synthesis of active esters using DCC are listed in Table 2. A list of Fmoc-Xaa-OR active esters that had been described to 1987 has been compiled.f l... 

The hydride is an excellent reagent for drying bydrocaibons, ethers (inclwling dioxane and tetrahydroftirane), amines (including pyridine), esters, the butanols (but not methanol or ethanol, which form alkoxides). Since the hydride is an effective condensation catalyst, it should not be used to dry aldriiydes, reactive ketones, acids, or acyl halides. Chlorides and bromides should be dried over calcium hydride only at moderate temperatures. 

The reagent reacts with vitamin Ai, a sensitive allylic primary alcohol, in methylene chloride-pyridine to give a crystalline ester useful for isolation of the vitamin... 

These reactions were studied in terms of steric effect, acidity and basicity of carboxylic acids, amines, and tertiary amines (e.g. pyridine) by using phosphorous acid and its mono-, di-, and tri-esters, as proposed in Scheme 1 for the case of the reaction with diesters. These N-phosphonium salts (i-4) were separated and characterized on the bases of the IR spectra, acid-base titration, and their reactions. 

Nothing remarkable has been reported, but a few useful results should be noted. Carboxylic esters at C-6 of the [1,2-a] fused system may be viewed as part of a vinylogous urethane, and are significantly less reactive than are those at C-5 <94TL2157>. 8-Hydroxyimidazo[l,2-a]pyridine showed useful oxine-like metal-chelating properties <91MI 810-02>. 

In a related process an ortho bromo ester is coupled with l-tri- -butylstannyl-2-ethoxyethene then acid used to close the ring the example below shows how this sequence is applied to a pyridine ester. 

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