Thiazoles, 2-acyl nucleophilic substitution

Combinations of N- and 5-alkylation in 2-imidazoline-2-thiols can lead to 5,6-dihydro-4//-imidazo[2,l-6]thiazoles when the heterocycles are treated with ketones in the presence of a halo-genating agent. This is a variant of the Hantzsch thiazole synthesis <92SC1293>. A further example of A-acylation in combination with nucleophilic substitution is the conversion of 2-chloro-2-imi-dazoline into (131) when it is treated with pyridine and an aryl isocyanate <87JCS(P1)1033>. 2-Imidazolines like clonidine are also known to A-nitrosate <93JCS(P2)59l>. Intramolecular alkylation is exemplified in the base-induced rearrangement of 2,5-diaryl-4-chloromethyl-2-imidazolines (132) into pyrimidines (Scheme 64) <93JOC6354>. 

Thiazoles, 2-acyl-, 13 formylation of, 73 halogeno-, 296, 347, 348 nucleophilic substitution of, 370... 

Heating thiazole with phenylazotriphenylmethane at 75 °C for 24 hours affords 2-phenyl-5-triphenylmethyl thiazole (75 Scheme 43). The 1-adamantyl radical and other nucleophilic alkyl and acyl radicals react with 2-substituted benzothiazoles in a homolytic ipso substitution yielding the corresponding 2-alkyl or 2-acylbenzothiazole (Scheme 44) (77CC316). 

Meso-ionic Thiazoles.—Successive treatment of 5-acylamino-AMhiazoline-2-thiones (73) with methyl iodide and alkali yields products that have been recognized as meso-ionic 5-acylimino-2-methylthio-thiazoles (75) (see also these Reports, Vol. 2, p. 614). This formulation supersedes the thiazolium salt structure by which certain members of this series have previously been represented. The methylthio-group of (75) is readily replaced on treatment with nucleophilic reagents such as potassium hydrosulphide, di-cyanomethide ion, amines, etc., with formation of 2-substituted 5-acyl-amino-A -thiazolines [e.g. (76)]. ... 

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