Selenazoles hydrazino

Bulka et al. (43) have demonstrated the electrophilic reactivity of selenazoles possessing an hydrazonc in the 2-position and nonsubstituted in the 5-position toward diazonium salt to give 5-phenylazo derivatives preferentially. For example, the main product of the coupling of 2-benzylidene hydrazino-4-phenylselenazole with diazo-o-phenetidine is the 5-(o-ethoxyphenylazo)-selenazole (Scheme 371 ruby red prisms, m.p. 206°C. yield 67"o). A formazan is obtained as by-product. (See Section III.6) (43). 

Selenazole, 2-aryl-4-chloromethyl-hydrolysis, 6, 344 Selenazole, 2-diethylamino-nitration, 6, 341 Selenazole, 2,4-dimethyl-oxidation, 6, 341 Selenazole, 2-hydrazino-oxidation, 6, 342 Selenazoles, 6, 339-347 electrophilic substitution, 6, 340 hetero fused synthesis, 6, 344 mass spectra, 6, 340 mesoionic... 

The free selenazole hydrazines are solids, sometimes well crystallized compounds. They show the typical properties of hydrazines. Thus they reduce Fehling s solution on warming and liberate silver, even in the cold, from ammoniacal silver nitrate solution. Further, they react with carbonyl compounds for example, benzylidene hydrazones are formed with benzaldehyde. These are identical with the hydrazones formed by direct condensation from benzaldehyde selenosemicarbazone and the corresponding a-halogenocarbonyl compound. 2-Hydrazino-4-phenylselenazole has also been reacted with acetophenone. The 2-a-methylbenzylidenehydrazone of 4-phenyl-selenazole (2, K = CJl, R" = H, R" = NH—N CMe-aH ) forms golden yellow plates mp 171°C. ... 

It has also been stated that the 5-position of selenazoles is more reactive toward electrophilic substitution than that of thiazoles. Such reactivity is still further increased by substituents in the 2-position of the selenazole ring, which can have an —E-effect. Simultaneously, however, an increasing tendency toward ring fission was observed by Haginiwa. Reactions of the selenazole ring are thus limited mainly to the 5-position which, specially in the 2-amino-and the 2-hydrazino-selenazoles, is easily substituted by electrophilic reagents. However, all attempts to synthesize selenazole derivatives by the Gattermann and by the Friedel-Crafts methods... 

As a result of various side reactions, the yields are relatively low. However, in no case was ring fission found during the oxidations. Specially noteworthy is the ease with which the two methine groups in the 5-position of the 2-hydrazino-selenazoles are coupled together. Reference to models indicates that the quinonoid dyes exist in the trans form. 

With the synthesis of the benzylidene hydrazones of selenazoles, it was possible to prepare formazans containing a selenazole ring. Of the compounds already described (Section I,C,1), 2-benzylidene-hydrazino-4,5-diphenyl- and 2-benzylidenehydrazino-4-methyl-5-carb-ethoxy-selenazole were used to couple with diazonium salts in order... 

Dinuclear cyanines, see Thiazoiocyanines 2,2 -Dioxo-A-3,3 -biselenazol-5.5 -inylidene-bis hydrazones, from 2-hydrazino-selenazoles, by oxidation with FeCl3 and H,Oj, 252... 

Alkylselenazoles, for example, 2,4-dimethylselenazole (b.p. 163-4°C/760mm), are generally liquids. Aryl or carboxylic acid derivatives, such as 2-methyl-4-phenylselenazole (m.p. 63 °C) are solids, except for some 2-phenylselenazoles which are liquids. 2-Amino and 2-hydrazino-selenazoles are almost always solids with the melting point increasing as the molecular weight increases... 

The 2-hydrazino-selenazoles (88 X = Se), and also the corresponding thiazoles (88 X = S), are obtained from the reaction between phenacyl bromides and seleno- or thio-semicarbazide under alkaline conditions. " Selenazolidine-2-carboxylic acid has been obtained by the reduction of selenocysteamine followed by treatment with Na02CCH0." ... 

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