1- Methyl-2-chloropyridinium

Mukaiyama et al. [44] developed an efficient method mediated by 1-methyl-2-chloropyridinium iodide and 2-chloro-6-methyl-l,3-diphenylpyridinium tetraflu-oroborate, wherein the reaction mechanism proceeds by the activation of acid followed by lactonization (Scheme 6.3). 

DCC, and l-methyl-2-chloropyridinium iodide (Mulcaiyama s reagent). Analogously, amides can be dehydrated with P2O5, pyridine, and AI2O3 to give ketenimines ... 

Miki and Hachiken reported a total synthesis of murrayaquinone A (107) using 4-benzyl-l-ferf-butyldimethylsiloxy-4fT-furo[3,4-f>]indole (854) as an indolo-2,3-quinodimethane equivalent for the Diels-Alder reaction with methyl acrylate (624). 4-Benzyl-3,4-dihydro-lfT-furo[3,4-f>]indol-l-one (853), the precursor for the 4H-furo[3,4-f>]indole (854), was prepared in five steps and 30% overall yield starting from dimethyl indole-2,3-dicarboxylate (851). Alkaline hydrolysis of 851 followed by N-benzylation of the dicarboxylic acid with benzyl bromide and sodium hydride in DMF, and treatment of the corresponding l-benzylindole-2,3-dicarboxylic acid with trifluoroacetic anhydride (TFAA) gave the anhydride 852. Reduction of 852 with sodium borohydride, followed by lactonization of the intermediate 2-hydroxy-methylindole-3-carboxylic acid with l-methyl-2-chloropyridinium iodide, led to the lactone 853. The lactone 853 was transformed to 4-benzyl-l-ferf-butyldimethylsiloxy-4H-furo[3,4- 7]indole 854 by a base-induced silylation. Without isolation, the... 

The title compounds were also synthesized from quinazoline precursors through the formation of their 1,4-oxazine rings. N-Methylisatoic anhydride was first condensed with ethanolamine to give N-(2-hydroxyethyl)-2-methylaminobenzamide (580). Cyclization of the latter with ethyl pyruvate gave quinazoline derivatives 581 which, upon hydrolysis and dehydrative cyclization with l-methyl-2-chloropyridinium iodide, afforded the l,4-oxazines[3,4- ]quinazoline (582) (8QJHC1163). 

The Mukaryama reagent,18 N-methyl-2-chloropyridinium iodide (6). transforms carboxylic acid 5 into the amide 7 The acid Is first activated in situ in the form of pyridinium salt 17 by an SN reaction with the Mukoixama reagent (6). This activation is a result of preventing resonance stabilization of the C-O double bond in the positively charged aryl ester 17. 

X = Cl, 02CCH=CH2, OH [ClC02Et, (PhO)2PON3, or methyl-2-chloropyridinium iodide]... 

Thiols react with halogenothiopyrylium salts to give the product of substitution. Thus 4-chlorothiopyrylium reacts with thiophenol to give the 4-thiophenoxythiopyrylium ion (75T2669). The reactivity of 4-chlorothiopyrylium and N-methyl-4-chloropyridinium toward thiophenol has been compared by a competitive experiment. The thiopyrylium ion was demonstrated to be ca. 4 times more reactive than the pyridin-ium ion. 

In 1976, Mukaiyama et al. [21] developed an efficient macrocyclization method mediated by l-methyl-2-chloropyridinium iodide (28). As shown in Scheme 10, the mechanism of this method is similar to that of Corey. It was found that triethylamine is the most suitable base and optimal yields were obtained in refluxing acetonitrile or dichloromethane. 

Mukaiyama and coworkers [24] found that 2-chloro-3-methoxymethyl-l-me-tbylpyridinium iodide is also suitable for effecting macrolactonization. Furthermore [25], the cyclization mediated by the 2-chloropyridinium salts described above sometimes gives no satisfactory yields. It is mainly due to the decomposition of the pyridinium salts under the cyclization conditions by the attack of triethylamine to either the 1-methyl group or the 2-position of the pyridinium ring to form 2-chloropyridine or 2-ammoniopyridinium salts. To solve this... 

The Mukaiyama reagent, l-methyl-2-chloropyridinium iodide (28), is also suitable for macrolactamization [85]. Jones et al. [86] achieved the first total synthesis of the important immunosupressant (-)-FK-506 (151) using the Mukaiyama method as a key cyclization step. As shown in Scheme 50, the unstable amino acid 149 was treated with 28 under high dilution to give the macrocycle 150 in... 

A general procedure is as follows. To l-methyl-2-chloropyridinium iodide (1.2 mmol, 1), was added a mixture of amine (1.0 mmol), carboxylic acid (1.0 mmol), and triethylamine (2.4 mmol) in dichloromethane (10 mL). After being refluxed for 1 hour under argon, the mixture was cooled to room temperature and ether (20 mL) added. The mixture was then washed with 5% aqueous hydrochloric acid solution (v/v, 50 mL) three times followed by water (1 x 50 mL). The organic layer was concentrated under reduced pressure and the carboxamide product was isolated by silica-gel column chromatography. 

Mukaiyama et al. [45] developed a direct lactonization of co-hydroxy acids by treatment with l-methyl-2-chloropyridinium iodide. The Mukaiyama method is... 

Finally, a heterocyclic derivative of tartaric acid should be mentioned, w hich has been used for the construction of boron enolates useful for allyl additions to carbonyl compounds (Section D. 1,3.3.3.). The eight-membered ring is formed from 2,3-O-benzylidenetartaric acid and lV,./V -dibenzyl-l,2-ethanediamine with the help of. V-methyl-2-chloropyridinium iodide as the condensing agent43. 

N-Alkylpyridones are demethylated when undergoing substitutions of this kind or are converted to pyridinium salts. For example, A-benzyl-3,5-dibromo-4-py idone (MI-620) and phosphorus pentachloride in toluene form 3,S-dibromo-4-chloropyridine and a small amount of N-benzyl-3,5-dibromo-4-chloropyridinium chloride. A -Methyl-5-nitro-2-pyridone and thionyl chloride in dimethylformamide give 2-chloro-l-methyl-5-nitropyridinium chloride. ... 

Me and rhodamine B (Rh B) were incorporated into polyethyleneimine and PVA by using diethylphosphoryl cyanide or l-methyl-2-chloropyridinium iodide as the coupling agent The SnOj coated with these films exhibited remarkably sensitized... 

A mixture of phenylacetic acid, benzyl alcohol, and tri-n-butylamine in methylene chloride added under argon to a mixture of l-methyl-2-bromopyridinium iodide and methylene chloride, and refluxed 3 hrs. benzyl phenylacetate. Y 97%. F. e., also with l-methyl-2-chloropyridinium iodide, s. T. Mukaiyama et al., Chem. Lett. 1975, 1045 Bull. Chem. Soc. Japan 50, 1863 (1977) carboxylic acid amides from amines (cf. Synth. Meth. 26, 367) s. ibid. 1975, 1163 3,4-dihydro-2H-pyrido-[1,2-a]pyrimid-2-one as acid scavenger cf. ibid. 1976, 13, 57 lactones from hydroxycarboxylic acids (cf. Synth. Meth. 17, 320) with 2-chloropyridine methio-dide and triethylamine s. ibid. 1976, 49 esters with 2 halogeno-3-ethylbenzothia-zolium salts of ibid. 1976, 267 2-chloro-N-methylbenzothiazolium triflate as condensing agent s. F. Souto-Bachiller, G. S. Bates, and S. Masamune, Chem. Com-mun. 1976, 719. 

A closely related set of conditions for the direct lactonization of to-hydroxyacids in good yield by treatment with l-methyl-2-chloropyridinium iodide and triethy-lamine has been reported.Masamune s lactonization procedure [Mercury(ii) methanesulphonate and disodium hydrogen phosphate with benzenethioesters of oj-hydroxyacids] has been utilized in a partial synthesis of the aglycone of the complex macrolide tylosin. 

Phosphorus chlorides have usually been used, but phosgene and thionyl chloride are also effective . Generally, heating l-alkyl-2-pyridones with phosphorus chlorides has led to the isolation of 2-chloropyridines, but in some cases the intermediate l-alkyl-2-chloropyridinium salt has been isolated (p. 223). l-Methyl-4-pyridone also produced 4-chloro-l-methylpyri-dinium chloride which gave 4-chloropyridine and methyl chloride when heated Other examples of the conversion of 1-substituted 4-pyridones into 4-chloropyridinium quaternary salts are known 7 Examples of that of l-aryl-2-pyridones into 2-chloropyridines are rarer but exist 25 ... 

With the great development of living radical polymerization (LRP), one can now easily prepare linear polymers with different monomers and functional chain ends. The past decade has seen a boost in new synthetic strategies for cyclic polymers. Lepoittevin et al. [78] pioneered a new synthetic method for cyclization of PSTY by combining NMRP and esterification. 4-Hydroxyl-2,2,6,6-tetramethyl-pyperidine-l-oxy (HTEMPO) and 4,4 -azobis(4-cyanovaleric acid) were used in a combination, yielding linear PSTY with both hydroxyl and carboxylic acid chain ends. Subsequently, the cyclization reaction was catalyzed by l-methyl-2-chloropyridinium iodide and triethylamine (Scheme 27). Because the esterification reaction is not highly efficient, especially when used in polymer systems, this method was only successful with low molecular weight PSTY (<4 kDa). 

---