L-Methylpyridinium-2-carboxylate

Reduction of carboxylic acids to aldehydes. 2 3-Acyllhiazolidine-2-thiones (2) can be prepared by reaction of l,3-thiazolidine-2-thione (1) with carboxylic acids directly (using 2-chloro-l-methylpyridinium iodide, 8, 95-96) or with acid chlorides (triethylamine or DCC). They can also be prepared from reaction of the thallium salt of 1 with an acid chloride. Yields by all four methods are 70-95%. The amides are reduced to aldehydes by either DIBAH or, generally in higher yield, by NaBH4 (90-98% yield). 

A novel synthesis of a-carboxyl, co-amino heterodifunctional polystyrene and its intramolecular cyclization was reported. Cyclic polystyrene with controlled size was synthesized by the intramolecular cyclization of linear a-carboxyl, co-amino heterodifunctional polystyrene under high dilution in the presence of 2-chloro-l-methylpyridinium iodide [67]. The linear precursor polymer was derived from a-diethyl acetal, co-amino heterodifunc-... 

Enantiomerically pure 1,3-thiazolidine-derived spiro /3-lactams 505 and 506 were stereoselectively synthesized by means of a Staudinger ketene-imine reaction in the presence of 2-chloro-l-methylpyridinium iodide (Mukaiyama s reagent) starting from optically active A -BOC-l,3-thiazolidine-2-carboxylic acid derivatives 504 and imines (Scheme 127). The reactions were stereoselective and afforded spiro-/3-lactams with a /ra r -configuration. The spiro-/3-lactams 505 and 506 were transformed into enantiomerically pure chiral monocyclic /3-lactams 507 and 508... 

An acyl transfer agent which can be used for the synthesis of acid anhydrides is obtained from the reaction of an acid chloride with 4-benzylpyridine (equation 24). In this way benzoic acid anhydride and cinnamic acid anhydride were obtained in 72% and 57% yields, respectively. As the intermediate, 1-acyl-4-benzylidene-l,4-dihydropyridines, can be isolated, Ais procedure should be well suited for the preparation of mixed anhydrides. Mixed aromatic and aliphatic anhydrides can be prepared with 2-ben-zoylthio-l-methylpyridinium chloride and salts of carboxylic acids. These reactions are carried out in aqueous solution. Iliey make use of the high reactivity of esters of thiocarboxylic esters towards nucleophiles. The mixed anhydrides of benzoic acid with 3-phenylpropanoic acid, phenoxyacetic acid, isobu-tyric acid, p-toluic acid and cinnamic acid were formed in 82, 79,61,91 and 66% yields, respectively. 

Methylpyridinium 3-carboxylate, 515 1-MethyIpyridinium methyl sulfate, 932 l-Methyl-2-pyridone, 932... 

When 1 is subjected to the carboxylate anion of 3 (TEA, R1CO2H), 2-acyloxy-l-methylpyridinium iodide (2) is formed. The hydrogen halide (HC1) is scavenged with triethylamine. A nucleophile (NuH) (4) such as an amine or alcohol in the presence of TEA adds to the carbonyl center of 2, yielding the desired product 5 and the by-product, l-methyl-2-pyridone (6). 

The activation of the carboxylic acids can be achieved also with the Mukaiyama reagent (2-chloro-l-methylpyridinium iodide, see p 308). Carboxylic acids react with this reagent, tri- -propylamine and imines in dichloromethane to give azetidin-2-ones [9]. 

ChIoro-l-methylpyridinium iodide 228 promotes esterification of carboxylic acids with alcohols as well as lactone formation of hydroxy acids in a basic medium (Mukaiyama 1977 [75]) ... 

The following reagents have been suggested for the activation of carboxylic acids in analytical procedures oxalyl chloride [490], N-ethyl-N -(3-dimethylaminopro-pyl)caibodiiniide [491,492], M/VT-carbonyldiiniidazole [493], and 2-bromo-l-methylpyridinium iodide [493]. 

In a recent example of p-lactam formation dehydration ofphenoxyacetic acid with 2-fluoro-l-methylpyridinium p-toluenesulfbnate in the presence of diaryhmines is proposed to proceed thorough the pyridinium intermediate 142 which leads to phenoxyketene, which reacts by [2 + 2] cycloaddition with the imine forming the product ds-P-lactam (Eqn (4.87)). Similahly propylphosphonic anhydride (T3P) was also successful in carboxylic acid activation (Eqn (4.88)). 

In alkali, acid and carboxylic acid anion reactions, 2,4-dichloropyridines have been converted into chloro-hydroxypyridines 79a, 7756, 840< usually of uncertain orientation. 2-Iodopyridine methiodide reacts with carboxylic acids in presence of triethylamine, giving 2-acyloxy-l-methylpyridinium ions 20 379). 

---