Nitrogen methyl iodide

The amino group activates the thiazole ring toward electrophilic centers. This point is illustrated by the rate constants of the reaction between 2-dialkylaminothiazoles (32) and methyl iodide in nitromethane at 25 C (Scheme 23) (158). The steric effects of substituents on nitrogen are... 

Curiously enough, bulky substituents on nitrogen increase this reactivity towards methyl iodide (119). This has been related to a steric decompression of the thiocarbonyl group in the transition state. Furthermore, knowledge of the ratio of conformers in the starting 4-alkyl-3-i-Pr-A-4-thiazoline-2-thiones and in the resulting 4-alkyl-3-i-Pr-2-methylthiothi-azolium iodides combined with a Winstein-Holness treatment of the kinetic data indicates that in the transition state, the thiocarbonyl bond is approximately 65% along the reaction coordinate from the initial state... 

The kinetics of the reaction between 2-methylthiothiazoles and methyl iodide show that the nucleophilic center is the ring nitrogen. The 2-methylthio group decreases the nucleophilicity of the this atom (269). 

Azolone anions are readily alkylated at nitrogen, e.g. 2-triazolone with methyl iodide gives the 1-methyl derivative. 

The 3-pyridylcarboxamide, prepared from the anhydride (Pyr, 99% yield), is cleaved (55-86% yield) by basic hydrolysis (0.5 M NaOH, rt) after quatemization of the pyridine nitrogen with methyl iodide. ... 

Examine the highest-occupied molecular orbital (HOMO of cyanide anion. Is the larger lobe on carbon or nitrogen Would you expect cyanide to act as a carbon or nitrogei nucleophile Does this lead to the lower energy transitioi state (compare the energy of cyanide-l-methyl iodide ( attack and cyanide+methyl iodide N attack) ... 

It is also interesting to note that quatemization of a chloropyrimi-dine at the nitrogen atom adjacent to the chloro group with methyl iodide results in the easy replacement of the chlorine by iodine, whereas similar salt formation on the remote nitrogen either leaves the chlorine unaffected or replacement occurs only at higher temperatures. A similar reaction occurs between 2-amino-6-chloro-4-methylpyrimidine and dimethyl sulfate in nitrobenzene to give the salt 45 and betaine 46. ... 

In a 1-substituted 1,2,3-triazole (79), both the 2- and 3-nitrogen atoms possess lone pairs of electrons that are available for quaternary salt formation, and quatemization is known to occur at the 3-nitrogen atom to give the symmetrical cation (80). Thus, the reaction between 1-methyl-l,2,3-triazole and benzyl iodide yields the same salt as is obtained from the interaction of 1-benzyl-1,2,3-triazole and methyl iodide the salt must therefore be 80 (R = Me, R = PhCH2,... 

The corresponding [5,4-6]-compound (107) was prepared similarly and treated with methyl iodide to give a quaternary salt which was shown to have structure 108, because mild alkaline hydrolysis gave 3-acetamido-l-methyl-2-pyridone. Again, quaternization took place on the pyridine-nitrogen, which is different from the behavior of the corresponding 1,4-diazaindene mentioned above. 

Methyl-thiazolo[4,5-/]quinoline 19 was methylated by methyl iodide on the nitrogen atom of pyridine giving the appropriate methodide. A subsequent oxidation with potassium hexacyanoferrate in alkaline media gave the 2,6-dimethyl-7-0x0-6,7-dihydrothiazolo[4,5-/]quinoline 21 (37LA60). 

The 2-methyl-4,9-dioxo-4,9-dihydrothiazolo[4,5-.g]quinoline was first quar-temized with methyl iodide on pyridine nitrogen and then treated with IV-methyl-quinolinium-4-yl salt, affording monomethine cyanine dyes 41 to study solva-tochromism, acid-base properties, and antimicrobial activities (95MI1). 

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