2-Chloro-l-methylpyridinium chloride

Medium-ring acetylenic lactones,2 Cyclization to medium size acetylenic lactones is difficult because of geometric constraint imposed by the triple bond, and has been considered practicable only for at least fifteen-membered rings. Surprisingly, the acetylenic w-hydroxy acid 1 when complexed with Co2(CO), is cyclized in 28% yield to the seven-membered complexed acetylenic lactone 2 by Mukai-yama s reagent, 2-chloro-l-methylpyridinium chloride (8, 95-96). The yield is essentially the same as that observed in lactonizaton to a complexed 10-membered... 

Acylhydrazines R CONHNHR (R = Ph or PhCH2 R = Bu, PhCH2 or Ph) are produced by the action of hydroxamic acids R CONHOH on the primary amines R NH2 in the presence of tosyl chloride or 2-chloro-l-methylpyridinium chloride . O-(Diphenylphosphinoyl)-A-aiylhydroxylamines 77 (R = NO2, Ac, Tos or CN) react with A-methylaniline to afford the hydrazine derivatives 78 . ... 

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). 

Related Reagents. 2-Chloro-l-methylpyridinium Iodide 1,3-Dicyclohexylcarbodiimide 2-Thiopyridyl Chloroformate Trimethylacetyl Chloride. 

Quaternary derivatives of 2- and 4 halogenopyridines are readily hydrolysed. Thus, alkali converts 2-chloro-l-phenacylpyridinium bromide into l-phenacylpyrid-2-one 4 , and other examples are known 28, 33ia, 949, Acid hydrolysis also occurs 28 that of l-ethyl-2-iodo-3- and -5-methylpyridinium iodides is accompanied by the formation of iodinated products 28, 4-Halo-geno-l-(4 -pyridyl)pyridinium chlorides give l-(4 -pyridyl)pyrid-4-one i7. 

Chloro-l-methylpyridinium iodide (1) reacts with a mixture of a carboxylic acid and an alcohol, in the presence of two equivalents of base, to form an ester (eq 1). The pyridinium salt (2) is formed rapidly by displacement of chloride from (1) by the carboxylate subsequent reaction with the alcohol results in formation of the ester, along with 1 -methyl-2-pyridone (3). A variety of solvents may be employed, but yields are highest in dichloromethane or pyridine. Tri-n-butylamine or Triethylanune are often used as base. The co-product (3) is insoluble in dichloromethane and so precipitates from this solvent. Good results are obtained even for hindered carboxylic acids and alcohols. 

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