5-Halo-l,2,3-thiadiazoles

Halo-l,2,4-thiadiazoles. On treatment with sulfuryl chloride, (1) undergoes oxidative cyclization to the 1,2,4-thiadiazole (2) in 80-100% yield.2... 

Aminothiadiazoles also react with halo aldehydes and halo ketones in a bidentate fashion to give imidazo[2,l-6][l,3,4]thiadiazoles (145). The NMR properties, aromatic character, basicity and crystal structure data are available (80JCS(P2)42l). Aminothiadiazoles also react with trichloromethanesulfenyl chloride to give the sulfenamide (146) which in the presence of an aromatic amine cyclizes to 3H-[l,3,4]thiadiazolo[2,3-c][l,2,4]thiadiazole (147) (75JOC2600). 

Several papers report on the nucleophilic reactivity of dithiocarbamate ions towards alkyl halides, 1,2-dibromoalkyl compounds, alkyl and aryl chloroformates, chloroacetic acid, chloroacetates, 3-halo-genophthalides, sulphenyl chlorides, sultones, and trialkylam-monium compounds. Examples of a similar reactivity of dithiocarbazate anions have also appeared. " A series of papers deal with addition or addition-elimination reactions of dithiocarbamate - or dithiocarbazate anions with w-nitrostyrene, 2-thioxo-, 2-oxo-, and 2-imino-5-methoxycarbonylmethylidene-4-thiazolidones, dimethyl acetylenedicar-boxylate, and NN -dialkyl phenylpropiolamidines. S-Monoalkylated N-cyanodithioimidocarbonates (492) underwent oxidative ring-closure to give 3-halogeno-l,2,4-thiadiazole sulphides (493) on treatment with halogenating agents. ... 

A useful method for the synthesis of 5-chloro-l,2,4-thiadiazoles (206) is the reaction of amidines with trichloromethylsulfenyl chloride (see Equation (30)). 3-Halo derivatives (349) (X = Cl, Br, I) (Equation (57)) have been obtained in moderate yields from the corresponding amines (348) via the Sandmeyer-Gatterman reaction <84CHEC-I(6)463>. 3-Chloro-l,2,4-thiadiazolin-5-ones (350) and (351) can be prepared by reacting chlorocarbonylsulfenyl chloride with carbodiimides or cyanamides respectively (Scheme 79) <84CHEC-I(6)463>. 

The a-halo ketone has also been prepared in situ (NBS, benzoyl peroxide, light) [89IJC(B)500]. Similarly, imidazo[2,l-b][l,3,4]thiadiazoles are accessible from 2-amino-l,3,4-thiadiazoles and acetophenones in the presence of hydroxy(tosyloxy)iodobenzene (HTIB). This latter method has been proposed as more convenient and versatile than the reaction of 2-amino-1,3,4-thiadizoles with a-halo ketones [94IJC(B)686, 94JCR(S)38, 94MI5],... 

When 2,5-diamino-l,3,4-thiadiazole is treated with an a-halo ketone in ethanol, the product is a 2-imino-3-(2-oxoalkyl)-5-amino-l,3,4-thiadiazoline hydrohalide (173). Direct treatment with excess hydrazine hydrate, or such treatment subsequent to reaction with aqueous ammonia, gives l-aminoimidazoline-2-thiones (Scheme 102) (70AHC(12)103). 

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