Regioselectivity in Reactions of Bis‐Hydrazonoyl Halides with Some Bifunctional Heterocycles

Abstract

Bis‐hydrazonoyl chloride 1 reacts regioselectively with 3‐mercapto‐1,2,4‐triazole 2a, 2,3‐dihydro‐3‐thioxo‐1,2,4‐triazin‐5(4H)‐one 2b and 2‐mercaptobenzimidazole 2c to give the hitherto unknown annelated 2,3‐bis‐(phenylhydrazono)thiazoles 6a‐c, respectively. Reactions of 1 with the methylthio derivatives of such heterocycles afforded the annelated 3,3′‐bis‐(1,2,4‐triazoles) 11a‐c, respectively. Similar reaction of 1 with 2‐phenylamino‐4(3H)‐pyrimidinones 4 gave 2,3‐bis(phenylhydrazono)imidazo[1,2‐a]pyrimidin‐5(1H)‐ones 16. Oxidation of 6c yielded the corresponding bis(phenylazo) derivative 15. The regiochemistry of the studied reactions is discussed.

A review on bis-hydrazonoyl halides: Recent advances in their synthesis and their diverse synthetic applications leading to bis-heterocycles of biological interest

“…Oxidation of the latter with lead tetraacetate in acetic acid yielded the bis -phenylazo derivative 108 . Similar reaction of the methylthio derivative 109 with I in refluxing pyridine yielded 110 [43] , [53] . When the reactions of I with each of 106 and 109 were carried out in ethanol in the presence of triethylamine, they yielded the same products 108 and 110 [43] .…”

“…Reaction of 5-phenyl-1,2,4-triazole-3-thione 89 with bis -hydrazonoyl chloride I in ethanol in the presence of sodium ethoxide at room temperature or in refluxing chloroform in the presence of triethylamine gave the 5,6- bis (phenylhydrazono)-2-phenyl-thiazolo[3,2- b ,1,2,4]triazole 90 ( Scheme 49 ) [40] , [53] .…”

“…Similarly, reaction of 6-benzyl-2,3-dihydro-3-thioxo-1,2,4-triazin-5(4H)-one 103a with bis -hydrazonoyl chloride I in ethanol in the presence of sodium ethoxide at room temperature gave a mixture of 104 (72%) and 105 (10%) ( Scheme 55 ) [53] . However, similar reaction of I with the methyl thio derivative of 103b yielded only 105 ( Scheme 55 ) [53] .…”

“…Similarly, reaction of imidazole-2-thione 106 with bis -hydrazonoyl chloride I in ethanol in the presence of sodium ethoxide at room temperature or in refluxing chloroform in the presence of triethylamine gave the 5,6- bis (phenylhydrazono)-2-phenyl-thiazolo[3,2- a ]benzimidazole 107 ( Scheme 56 ) [43] , [53] , [57] . Oxidation of the latter with lead tetraacetate in acetic acid yielded the bis -phenylazo derivative 108 .…”

Synthesis of a new triheterocycle. Bis-pyrazolo[1,5-a][4',3'-e]pyrimidine

“…In continuation of our studies dealing with the utility of hydrazonoyl halides for synthesis of various heterocyclic ring systems, [1][2][3][4][5][6][7][8][9][10][11] we wish to report herein a new facile synthesis of bispyrazolo [1,5-a][4',3'-e]pyrimidine ring system and its various functionalized derivatives that have not been reported hitherto. The earlier methods reported for synthesis of such ring system are multisteps.…”