Thiosemicarbazides, synthesis

Cyanate condensation products of carbohydrazide, synthesis 11 Thiosemicarbazide, synthesis 12 Dithiocarbamates of selenium(II) and tellurium (II), synthesis 32 Aluminum phosphide, synthesis 7 Phosphorus(III) fluoride, synthesis 49... 

Thionyl fluoride, as by-product in sulfur tetrafluoride reactions, 41, 105 toxidty of, 41,105 Thiophene-2-OL, 43, 55 2(5H)-Thiophenone, 43, 55 Thiosemicarbazide, in synthesis of 1,2,4 triazole, 40, 99 reaction with formic acid to yield l-formyl-3-thiosemicarbazide, 40,99... 

The microwave-assisted solid-supported synthesis of 1,3,4-thiadiazoles was described applying from acid and thiosemicarbazide on acidic aliunina... 

Synthesis of 2-heterocyclic thiosemicarbazones can be summarized in three reaction sequences following the lead of Klayman et al. [5]. Condensation of equimolar quantities of a thiosemicarbazide and a 2-heterocyclic aldehyde or ketone in an alcoholic solvent is represented by Eq. (1). The product s superscripts refer to positions of substitution in the thiosemicarbazone moiety in accord with lUPAC. 

The literature describes a general method for the synthesis of l,4-dioxo-3,4-dihydrophthalazine-2(l/7)-carbothio-amide 655 based on heating an equimolar mixture of phthalic anhydride and thiosemicarbazide at 160 °C for 30 min in the presence of PPA. However, it has been reported that this treatment provides 654 instead (Scheme 107) <2003JHC1011>. 

Several 3-mercapto-l,2,4-trizines have been synthesized through the condensation of thiosemicarbazide with diketones under microwave irradiation in a solventless system <06PS87>. The synthesis and cyclocondensation reactions of 3-substituted-5-(2-aminobenzyl)-l//-[l,2,4]triazin-6-ones have been reported <06JHC613>. 

The synthesis of 6-oxo-2,3,4,6-tetrahydro[l,2,4]triazino[5,6-c]isoquino-line-3-thione 178 was achieved by the reaction of the keto acid 174 with thiosemicarbazide to give azauracil 175. Its esterification gave 176, which was converted to the amide 177 and cyclized (84PHA186 92CCC123) in presence of acetic acid to give 178. 

An alternative synthesis of this ring system involved the construction of the triazine ring at the first stage. Thus, the reaction of diethyl oxomalo-nate either with thiosemicarbazide followed by methylation or with S-... 

This ring system has been covered in several reviews <1984CHEC(5)305, 1984CHEC(5)607, 1987AHC(41)319, 1996CHEC-II(8)345, B-2002SOS(12)613>. The methods used for synthesis are quite diverse, and include the reactions of thiosemicarbazide with 1,3,5-tricarbonyl compounds and unsaturated dicarbonyl compounds, or their equivalents. 

Jain and Handa reported [82IJC(B)732] that the mode of ring closure may depend critically on the 5-substituent of the triazole. 3-Mercapto-5-(4 -pyridyl)[l,2,4]triazole 143 was reacted with phenacyl bromides to give 144, which on treatment with PPA resulted in the formation of thiazolo[2,3-c][l,3,4]triazoles 145. The structure of 145 [R = (4-Cl)C6H4] was proved by an independent synthesis starting with isonicotinyl thiosemicarbazide. 

The synthesis of numerous thiadiazoles substituted in the 5-position with carbamoyl or heteroaryl moieties and hydroxyl or amino groups in the 2-position (Scheme 20), was achieved by reacting dithioesters with semicarbazide or thiosemicarbazide and cyclizing the resulting acylated sem-... 

Aza transfer between diazonium salts and 4-substituted thiosemicarbazides is a convenient and very fast method ( 15 min) for synthesis of 5-aminothiatriazoles ( 60% yield) introduced by Stanovnik et al. <780PP59>. 

Amino-5-alkyl- or 5-phenyI-l,3,4-thiadiazoles are prepared most conveniently from thiosemicarbazide. For example, benzalthiosemicarbazone by oxidation with iron(III) chloride gives the 5-phenyl derivative. Thiosemicarbazide is also used in the synthesis of 2-amino-5-mercapto-l,3,4-thiadiazole by reaction with carbon disulfide. The product may be alkylated to yield the 5-alkylthio derivatives using a variety of alkylating agents (58MI11201). 

Reaction of acylcyanides (485) with amidrazones (453), semicarbazide (459a), thiosemicarbazide (459b) or aminoguanidine (460a) is used for the synthesis of 5-amino-... 

The reaction of 1,2-dicarbonyl compounds with amidrazones, semicarbazide, thiosemicarbazide and aminoguanidine has also been used for the synthesis of condensed 1,2,4-triazines. Cyclohexane-, cycloheptane- and cyclooctane-1,2-diones (489) with amidrazones (453) afford the cycloalkatriazines (490) (78HC(33)189, p.66l). 

In a similar way, reactions of phenanthroquinone, chrysenoquinone, ninhydrin, acenaph-thoquinone or phenalene-l,2,3-trione with amidrazones (453), semicarbazide (459a), thiosemicarbazide (459b) or aminoguanidine (460a) have been used for the synthesis of phenanthro[9,10-e][l,2,4]triazines (503), chryseno[5,6-e][l,2,4]triazines (504), indeno[l,2-e][l,2,4]triazines (505), acenaphtho[l,2-e][l,2,4]triazines (506) and phenaleno[l,2-e][l,2,4]triazines (507), respectively (78HC(33)189, pp. 740-748). 

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