2-Imino-l,3,4-thiadiazoline

Imino-l,3,4-thiadiazoline. See under Aminothiadiazole A262-R Impact-Friction Pendulum Test as conducted at the Spencer Chemical Co, Kansas City, Mo A354 (Note d)... 

Dimethyl 2-(arylamino)thiazole-4,5-dicarboxylates 546 are produced from 3-aryl-5-benzoyl-2-imino-l,3,4-thiadiazolines 542 and dimethyl acetylenedicarboxylate. It is suggested that the initial adducts 543 rearrange to the betaines 544 by a proton shift and that the betaines cyclize to the hypervalent sulphur compounds 545. Subsequent loss of benzoyl cyanide yields the products . 

Various 2-substituted l,3,4-thiadiazoline-5-thiones can be prepared in good yield by the reaction of amidrazones with CS2 in ethanol at room temperature (Scheme 21a) (70CPB1696). 4-Aryl-2-benzoyl-5-imino-A2-l,3,4-thiadiazolines are prepared from activated thiocyanates and benzenediazonium chloride, presumably via a hydrazone (Scheme 21b) (75TL163). 2-Thio- and 2-amino-l,3,4-thiadiazoles carrying a carbamate in the 5-position are obtained in one step by the reaction of a dithioimidate with a hydrazide. The yields are quite high (Scheme 22a) (80ZC413). 

Amino-2-imino-3-phenacyl-l,3,4-thiadiazoline (66) undergoes theDimroth rearrangement to yield the 1,2,4-triazole derivative (67 Scheme 6) (75M1291). 

Treatment of 2,5-diamino-l,3,4-thiadiazole with an a-haloketone in ethanol, followed by reaction of the resulting 2-imino-3-(a-keto-alkyl)-5-amino-l,3,4-thiadiazoline hydrohalide (33) with aqueous ammonia, and then excess of hydrazine hydrate, leads to 1 -amino-imidazole-2-thiones (34).144... 

The numbering of the 1,3,4-thiadiazole ring follows from 1. Clockwise or anticlockwise numbering is used according to convenience. In 2- or 5-imino-, -oxo-, or -thiono-l,3,4-thiadiazoles, the position of the extra hydrogen atom is shown by the corresponding number in parentheses, e.g., l,3,4-thiadiazolin-2(3)-one (2). 

Akerblom and Skagius - and Skagius have prepared 3-alkyl-l,3,4-thiadiazolin-2(3)-ones (95) from aminothiadiazoles (4) by ring-alkylation to 95, nitrosation of the imino group to 96, and thermal decomposition of the nitrosamine to 97. The reaction seems to be quite general, since it has been performed with R = amino, alkoxy, and 2-nitro-5-furyl. ... 

Imino-4-phenyl-2-(trifluoromethyl)-A2-l,3,4-thiadiazoline (5) Typical Procedure 112... 

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). 

Ferric chloride 2-Amino-l,3,4-tbiadiazoles from 2-imino-zl -1,3,4-thiadiazolines from thiosemicarbazones... 

The product obtained from phenylthiosemicarbazide (92 R = H) and phosgene, described as 2-amino-4-phenyl-l,3,4-thiadiazolin-5-one (93 R = H), is in fact a mixture. Conditions have now been specified for the successful preparation of this compound (93 R = H) by this route. Oxidation of thiosemicarbazones. The oxidative cyclization of benzalthio-semicarbazones and of acetone thiocarbohydrazone is a well-known route to the 1,3,4-thiadiazole ring system. 4-Arylthiosemicarbazones of ketones (99) have now been shown to cyclize in this manner on being stirred in benzene in contact with suspended manganese dioxide, giving satisfactory yields of 5-imino-A -l,3,4-thiadiazolines (101). Ring-closure over alumina in chloroform slowly yields the isomeric l,2,4-triazoline-5-thiones (100). Bicyclo[3,3,l]non-2-en-9-one 4-phenylthiosemicarbazone... 

The partial inhibition of the hydrolysis observed at pH < 4, and the negative salt effect, may be attributed to a specific cation-anion interaction. The proposed mechanism receives further support from the observed effects on the hydrolysis rates of increased viscosity of the medium and of added inorganic nucleophiles. Hydrazine or alkylhydrazines cleave and recyclize 1,3,4-thiadiazolium salts (114) to 1,2- or l,4-dihydro-l,2,4,5-tetrazines (115) in high yield. The action of arylhydrazine results in the alternative recyclization of the probable intermediate ArNHN=CR2NR N=CR SH, to 4-amino-1,2,4-triazolium salts (116). 5-Amino-2-imino-3-phenacyl-l,3,4-thiadiazolines (117) isomerize in boiling ethanol to 5-amino-3-mercapto-l-phenacyl-l,2,4-triazoles (118). This example... 

Other Syntheses. 3,5-Diaryl-l,3,4-thiadiazoline salts (139) are accessible by the cyclization of the appropriate substituted l-phenyl-2-thiobenzoyl-hydrazines by triethyl orthoformate in ether saturated with hydrogen chloride, The condensation of phenacyl thiocyanates ArCOCHaSCN, with diazotized arylamines provides a convenient one-step synthesis of 4-aryI-2-benzoyl-5-imino-A -l,3,4-thiadiazolines (141). Their alternative synthesis from (140) and potassium thiocyanate confirms the assigned structure. ... 

Cl i,Hi 2N2S, 3-Phenyl-2-phenylimino-l,3-thiazetidine, 44B, 362 Cl Hi2 80283, 4-(6-Methoxy-3-pyridinyl)-5-[(6-methoxy-3-pyridinyl)-imino]-l,2,4-dithiazolidine-3-thione, 46B, 406 Cl nH, 2N11S, 5-Imino-4-phenyl-3-phenylamino-4H-l,2,4-thiadiazoline, 44B, 363... 

Cyano-l,2,4-thiadiazole-5-carboximidate 5-Imino-A3-l,2,4-thiadiazoline 3,5-Bis(diphenylamino)-l,2,4-thiadiazole... 

Thiadiazolines are less stable compared to 1,2,4-thiadiazoles and this can be attributed to the loss of aromatic character. They are readily cleaved at the N-S bond under fairly mild conditions (H2S in pyridine) in some cases, the product from ring cleavage can recyclize to give new heterocyclic ring systems. The 3-imino-l,2,3-thiadiazoline 24 when reduced with H2S affords the two J-triazine derivatives 25 and 26 (Scheme 3) <1996CHEC-II(4)307>. 

A somewhat similar conversion was found when the 3-anilino-4-phenyl-5-imino-l,2,4-thiadiazoline (Hector s base) was heated with ammonia. 

The condensation of 5-amino-3-methyl-l,2,4-thiadiazole (118) with aliphatic or aromatic nitriles yields 1 1 adducts, which are, according to their H NMR spectra, equilibrium mixtures of (119) and (120) (Scheme 28) <82AHC(32)285>. These adducts are produced by a bond switch at the n-hypervalent sulfur in (121). X-ray analysis of the adduct formed from the reaction of (118) with chloroacetonitrile showed the adduct to exist as (122) in the crystals <81AX(B)185>. Further examples of this type of bond switch at rc-hypervalent sulfur are observed in the reaction of 5-imino-1,2,4-thiadiazolines with various electrophilic reagents (Section 4.08.6.1). 

The oxidation of A-arylthioureas produces Hectors bases which readily isomerize to give 3,5-diamino-1,2,4-thiadiazoles (Equation (28)). Imidoylthioureas (228) when treated with A-chloro-succinimide afford 5-imino-l,2,4-thiadiazolines (229) (Scheme 49) <85S83>. 

Amino-1,2,3,4-thiatriazole (10) has been described as reacting with equal amounts of JV-phenyl benzimidoyl chloride (109) to give 5-imino-A -l,2,4-thiadiazoline hydrochloride (110) in 80% yield (Scheme 20). The thiadiazoline is decomposed by strong base into JV-cyanoamidine (111) and sulfur, but the free base (112) can be liberated by treatment with bicarbonate. The free base decomposes similarly into V-cyanoamidine (111) and sulfur when heated in chloroform or water. 

Methylamino-l,2,4-thiadiazole (195) (but not its 3-phenyl homolog) arises irreversibly171 by isomerization of 5-imino-4-methyl-1,2,4-thiadiazoline (193) in ethanol on prolonged storage or brief heating.81, 171 The structure is confirmed by its alternative synthesis from 201.6 Further methylation (of 195) (to 194, and 194 + 196 when R = Ph) follows the general scheme.81... 

Other structures which have been confirmed polarographically are those of 5-imino-[benzthiazolo-(2,3-6)]-l,2,4-thiadiazoline (357) and N-thiocyanato-5-imino-[benzthiazolo-(2,3- )]-l,2,4-thiadiazoline (358).180 A polarographic technique has been employed165 for demonstrating the absence of acidic hydrogen in 2,4-dimethyl-l,2,4-thiadiazolidine-3,5-dithione. 

Alkyl-5-imino-3-methyl-A2-l,2,4-thiadiazolines react exothermally at 0°C with dibenzoyl or dimethoxy carbonylacetylenes in tetrahydrofuran to give the 2-aIkylaminothiazoles in high yields (1564). The cyclo addition reaction of 2-pyridyl isothiocyanates with 1-azirines results in the formation of 2-pyridylaminothiazoles (1565). 

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