Chemistry of Heterocyclic Diazo Compounds

Abstract

The preparation, chemical properties and synthetic utility of nitrogen heterocyclic diazo compounds are reviewed. IBTRODUCTIOB : Heterocyclic diazo compounds (1) and their diazonium salts (2) are versatile reagents and their chemistry ha8 received a considerable recent attention!" However, in spite of their interesting synthetic potentialities, the chemistry of this class of compounds has been ignored in available organic chemistry bocks. Moreover, with exception of Tedder's chapter in "Advances in Heterocyclic Chemistryn5which is now obsolete, no trials to review the chemistry of this class of compounds has been made. In the following we report the literature in this area which we hope will be of value for both researchers and imtmctors of organic chemistry. PREPATtATIOB : The common method for the synthesis of heterocyclic diazo compounds or diazonium salts is the diazctization of heteroaromatic primary amines in which the amino group is bonded directly to the ring (cf. Bq. 1). Entler4 has covered in details this m b -5 ject. Stadtler et a 1 reviewed the other methods for the synthesis of this class of compounds, but these methods are of minor importance. bese Y-Z .2 -1 HC1 --Eq. 1 CHEXICAL PROPERTIES: The diazo compounds can be converted into other derivatives. The reactivity and types of reactions undergone by these compounds are 8ummarisr.d in this review. 1. Intramolecular cyclization: Heterocyclic diazo compounds are considered as dipolar compounds. Thus, interaction between the positive and negative ends of the molenrle leads to the formation of fused Diazotization of 4-duo-3-phenyl-5-benzylpyrazole (2) has afforded the corresponding diazopyrasole derivative (4). Compound 4 when heated in 8 acetic acid has afforded the pyraeolo 3,4-c pyrasole derivative (5). Similarly, the pyrazolo 3,4-e -1,2.3,4-tetrazine (6) has been formed when a solution of diazotised 5-amino-4-phenylazopyrazole was left to stand at room temperature in protic media. One of the most efficient routes for the synthesis of aeopurinee is the self coupling of diazotized dnoimidazole.derivatives via amide or amidic nitrogen at 5-poaition.l0 Recently a survey of this synthetic route for obtaining derivatives of these ring systems has been reviewed!' 3-A1nino-4-methylquinoline (1) reacts vith two molecules of nitrous acid to form the quinolino-O-triazine derivative (g) aud 1 2 * 1 3 On the other hand, when the reaction 3-azidoquinolino-4-carboxaldehyde (2).was carried out in the presence of aulphuric acid, compound 10 was formed. 6-Rethyluracil (11) behaves similarly on diazotization13 (cf. Chart 1).

Studies on Fused Azoles: Synthesis of Several Polyfunctionally Substituted Fused Azoles

“…Di azo tised aminopyrazoles have been re ported to re act with ac tive meth y lene re agents to yield ei ther hy dra zones which readily cyclise into pyrazolo [5,1-c] [1,2,4]tri azines or di rectly into the cy clic prod uct via a cycloaddition re ac tion un der the cou pling con di tion. 14,15 It has been found that diazotization of 2 af fords diazonium salt 19 which was coupled with ethyl cyanoacetate to yield a com pound of mo lec ular for mula C 12 H 15 N 5 O 5 S (M + = 325 m/z). The IR spec tra showed ab sorp tion bands for both cyano and es ter car bonyl groups at = 2200 and 1725, 1710 cm -1 .…”

Recent developments in aminopyrazole chemistry

“…93 Diazotization of 3-amino-1-phenylpyrazole (154) gave the corresponding diazonium salt 155 that reacted with 156 to yield 157 that was readily cyclized into 158 (Scheme 41). A novel green iodination of 3-aminopyrazole was described with iodine and hydrogen peroxide in water to give 4-iodo-3-aminopyrazole in 82% yield.…”

Synthesis of Pyrazolo[1,5‐a][1,3,5]triazine, Pyrazolo[1,5‐a]pyrimidine, and Imidazo[1,2‐b]pyrazole Derivatives Based on Imidazo[2,1‐b]thiazole Moiety

“…Diazotized aminopyrazoles have been reported to react with active methylene reagents to yield hydrazones, which either readily cyclize into pyrazolo[5,1‐ c ][1,2,4]triazines or directly into the cyclic product via a cycloaddition reaction under the coupling conditions . It has been found that diazotization of 5‐aminopyrazole derivative 6 affords diazonium salt 34 , which was coupled with ethyl cyanoacetate to yield a compound, which was identified as ethyl 2‐cyano‐2‐(2‐(4‐(2‐(1‐(3‐methyl‐6‐phenylimidazo[2,1‐ b ]thiazol‐2‐yl)ethylidene)hydrazinecarbonyl)‐3‐(phenylamino)‐1 H ‐pyrazol‐5‐yl)hydrazono)acetate ( 35 ).…”