Diazo-1,3,4-thiadiazoles

A number of other heterocycHc diazo components such as thiazole, iadazole, thiophenes, and thiadiazole types (see Fig. 1), as well as heterocycHc couplers, ie, 6-hydroxy-2-pyridinone [626-06-2] barbituric acid [67-52-7] and tetrahydroquiaoline [25448-04-8] h.2L e been cited ia the Hterature (90,91). Reviews on disperse dyes have been pubUshed (92,93). 

An interesting rearrangement was found by Davies and Kirby (1967) in the diazo-tization of 7-amino-benzothiazole (6.68). As Scheme 6-45 shows, the diazonium ion formed initially rearranges under hydrolytic conditions into 7-amino-l,2,3-benzo-thiadiazole (6.69). 

Whereas methyl 5-(3-methyl[l,2,4]thiadiazolyl)diazoacetate 56 shows no tendency to cyclize to 7-methoxycarbonyl-3-methyl[l,2,3]triazolo[3,4-A][l,2,4]thiadiazole 57, the 5-(l-diazoalkyl)substituted [l,3,4]thiadiazoles 58 are in equilibrium with the fused bicyclic form, the [l,2,3]triazolo[5,l-A]][l,3,4]thiadiazoles 59 <1988BSB795, 1992JHG713>. The latter ring-closed form 59 prevails in the solid state as indicated by infrared (IR KBr disk). The chain/ring equilibrium of the diazoimine/triazole forms is shifted toward the open-chain diazo form 58 by raising the temperature and by using less polar solvents (Equations 8 and 9). 

Scheme 12 shows synthesis of 1,2,3-thiadiazoles by the Wolff, Hurd-Mori and Pechmann-Nold methods. Pechmann s and Wolffs are the oldest of the methods. The Pechmann-Nold synthesis involves the [3 + 2] cycloaddition of diazo-compounds to isothiocyanates or thiocarbonyl compounds (modified Pechmann synthesis). The use of thiocarbonyl compounds in the [3 + 2] cycloaddition step has broadened the scope of this reaction and made the starting materials more readily accessible. Wolffs method requires the synthesis of diazoketones that are treated with a thionating reagent to produce 1,2,3-thiadiazoles. With the development of new methods of diazotransfer reactions, the diazoketone precursors have become easily attainable and with further attention to the thionating reagents, this reaction is also useful for the synthesis of 1,2,3-thiadiazoles. 

Amino-l,2,4-thiadiazoles (129) are diazotised at — 10°C in phosphoric acid, and couple in the usual way with reactive aromatic compounds such as naphthol, giving moderate yields of diazo dyes <82AHC(32)285>. Diazotization of (129) (R = H and Ph) may be accomplished using aqueous sodium nitrite and hydrochloric acid. Treatment of the resulting salt with sodium azide yields the 3-azido derivative (130) (Equation (17)) <86CC800>. 

A -1,3,4-Thiadiazoline-1 -oxides (146) (Equation (18)) are formed by addition of diazo compounds (R2C=N2) to sulfines (R R C =S=0). The adducts from diazomethane and aryl substituted sulfines are unstable and give the thiadiazole (147) via a Pummerer-type aromatization <84CHEC-I(4)545>. The A -thiadiazoline-1,1-dioxide (149) has been produced by oxidation of the hydrazone (148) (Equation (19)) and treatment with sulfur dioxide <84CHEC-i(4)545>. 2-Alkylidenethiadiazolines can be obtained from the dipolar addition of diazo compounds to thioketenes <83CB66, 90TL3571, 92HCA1825>. 

In some instances, sterically encumbered 2,5-dihydro-l,3,4-thiadiazoles do not eliminate nitrogen. Instead, cycloreversion leading to the starting materials or a new pair of diazo- and thiocarbonyl compounds was reported. Thus, a crystalline product of type 20, obtained from di(ferf-butyl)diazomethane and 2-benzyl-4,4-dimethyl-l,3-thiazole-5(477)-thione, was found to dissociate in solution to give the starting materials (42). In the case of (ferf-butyl)(trimethylsilyl)thioketone and... 

The preparation of thiiranes is most conveniently performed in solution. However, there are also protocols reported for reaction in the gas and solid phase. By using diazo and thiocarbonyl compounds in ether as solvent, both alkyl and aryl substituted thiiranes are accessible. As indicated earlier, aryl substituents destabilize the initially formed 2,5-dihydro-1,3,4-thiadiazole ring and, in general, thiiranes are readily obtained at low temperature (13,15,35). On the other hand, alkyl substituents, especially bulky ones, enhance the stability of the initial cycloadduct, and the formation of thiiranes requires elevated temperatures (36 1,88). Some examples of sterically crowded thiiranes prepared from thioketones and a macro-cyclic diazo compound have been published by Atzmiiller and Vbgtle (106). Diphenyldiazomethane reacts with (arylsulfonyl)isothiocyanates and this is followed by spontaneous N2 elimination to give thiirane-2-imines (60) (107,108). Under similar conditions, acyl-substituted isothiocyanates afforded 2 1-adducts 61 (109) (Scheme 5.23). It seems likely that the formation of 61 involves a thiirane intermediate analogous to 60, which subsequently reacts with a second equivalent... 

Silyl-substituted diazoketones 29 cycloadd with aryl isocyanates to form 1,2,3-triazoles 194 (252) (Scheme 8.44). This reaction, which resembles the formation of 5-hydroxy-l,2,3-triazoles 190 in Scheme 8.43, has no analogy with other diazocarbonyl compounds. The beneficial effect of the silyl group in 29 can be seen from the fact that related diazomethyl-ketones do not react with phenyl isocyanate at 70 °C (252). Although the exact mechanistic details are unknown, one can speculate that the 2-siloxy-1-diazo-1-alkene isomer 30 [rather than 29 (see Section 8.1)] is involved in the cycloaddition step. With acyl isocyanates, diazoketones 29 cycloadd to give 5-acylamino-l,2,3-thiadiazoles 195 by addition across the C=S bond (252), in analogy with the behavior of diazomethyl-ketones and diazoacetates (5). 

These and other experiments show that diazonium salts incorporating the 1,2,4-thiadiazole ring are undoubtedly among the most reactive examples of their kind.80 Their reactivity is attributable to the electron deficiency of the terminal nitrogen of the diazo group and depends in turn on the electron-attracting nature of the heterocyclic nucleus.80... 

Diazo ketones are converted by amines into 1,2,3-triazoles and by hydrogen sulfide into 1,2,3-thiadiazoles (371 — 372 Z = NR, S). The intramolecular cyclization of suitable precursors is a most useful method for the preparation of the 1,2,3-triazole ring, including (V-amino- and (V-imino-triazoles and triazole N-oxides. 

A-Azidocarbonylazepine, 2724 Azidocarbonylguanidine, 0816 4-Azidocarbonyl-1,2,3-thiadiazole, 1066 4-Azido-3-diazo-3//-pyrazolo[3,4-b]quinoline, 3231b 2-trans-1 -Azido-1,2-di hydroacenaphthyl nitrate, 3460 /V-Azidodimethylamine, 0911... 

Among heterocyclic diazo components an especially favored starting material is 3-phenyl-5-amino-l,2,4-thiadiazole, which is also used in the production of disperse dyes. It yields very bright dyes for coloring polyacrylonitrile [31], An example is 9 [85283-77-8]. 

In addition, the following have been described as diazo components 2,5-dichloro-4-nitroaniline (red) [49], 2-chloro-5-trifluoromethylaniline (yellow) [50], 4-nitro-2-trifluoromethylaniline (red) [51], 2-amino-5-trifluoromethyl-l,3,4-thia-diazole (red) [52], 3-methylmercapto-5-amino-l,2,4-thiadiazole (red) [53], 3-methyl-4-nitro-5-aminoisothiazole (blue-violet) [54], 2-amino-6-chlorobenzothia-zole (red) [55], and 3-amino-5-nitro-7-bromobenzisothiazole (blue with a red cast) [56],... 

Thiadiazol 5-(Diazo-methyl)-4-phenyl- E14b, 995 (Oxim + H2N-C1)... 

---