Thioamides methylations, diazomethane

Alkylation and Arylation. The 5-methylation of thioamides by diazomethane is catalysed by silica gel. 5-Phenyl derivatives of thiobenzanilides are obtained in high yield by radical arylation with nitrosoacetanilide or phenylazotriphenyl-methane. Thiols are made from alkyl (or cycloalkyl, or aralkyl) halides by their reaction with dimethylthioformamide and treatment of the imidium ester with methanol other methods of hydrolysis lead to side-reactions, giving impure products. Mono- and bi-protic thiocarboxamides condense with ethyl bromo-cyanoacetate and one equivalent of NaOEt with spontaneous separation of sulphur and the formation of ff-amino-cr-cyano-acrylates, as shown in reaction (5). The... 

Treatment of the cyclic amide 157 or the dihydro compound 159 with Lawesson s reagent gives the corresponding thioamides 158 and 160 (Equation 20) <1999JME1661>. Methylation of the cyclic amide 161 with diazomethane gives a mixture of 0,0- and TV,O-dimethyl products 162 and 163 in a ratio of 7 6 (Equation 21) <1996EJM651>. 

Reaction of A -substituted thioamides (391) with chlorocarbonyl isocyanate at room temperature affords good yields of 1-imino derivative (392) which can be quantitatively A -methylated with diazomethane to (393) (Scheme 82) <848771 >. 

Amides can also be methylated with diazomethane in the presence of silica gel however, the reaction requires a large excess of diazomethane (25-60 equiv, eq 16). The reaction primarily provides O-methylated material however, in one case a mixture of O-and A-methylation was reported. Thioamides are also effectively methylated with this procedure to provide S-methylated compounds. Finally, amines have been methylated with diazomethane... 

Methyl dithiocarbamates attack the reactive methylene groups of cyano-acetamide, cyanoacetic ester, or bis(phenylsulphonyl)methane with loss of methanethiol and formation of the thioamides R R CHC(S)NR R . Diazomethane and phenyldiazomethane, which is more reactive, insert into dialkyl-aminomethyl esters of dialkyldithiocarbamic acids (152 X = NR R ) or ethyl xanthic acid (152 X = OEt), giving esters (153 R = H or Ph, X = NR R or OEt) that have an extended alkylene chain. ... 

In contrast to thioamides, their S-oxides can be methylated with diazomethane. —E A soln. of diazomethane in n-heptane added in one portion to a soln. of thiobenzanilide S-oxide in methanol-chloroform, and the product isolated after 40 min. N-methylthiobenzanilide S-oxide. Y 60%. F. e. s. W. Walter et al., A. 660, 60 (1962). 

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See also in sourсe #XX -- [ ]

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