Condensation of 1,2-dicarbonyl compounds with modified Huisgen zwitterions: synthesis ofN-aryl–N-acyl hydrazones

Abstract

The reactivity patterns of the modified Huisgen zwitterions derived from arylazocarboxylates toward 1,2-dicarbonyl compounds have been studied for the first time for a facile synthesis of N-aryl–N-acyl hydrazones.

Sequential annulation and isomerisation reaction of 3-acylmethylidene oxindoles with Huisgen zwitterions and synthesis of 5-(3-oxindolyl)oxazoles

“…Although a precise mechanism of this sequential annulation/isomerisation reaction remains elusive, on the basis of our results and related reports, 14–16 we proposed a possible mechanism as shown in Scheme 3. The reaction sequence is initiated with the formation of the reactive HZ from PPh 3 and azodicarboxylate.…”

“…13 Over the past two decades, HZs have attracted remarkable interest owing to their versatile reactivity with various electrophiles in carbon–nitrogen bond formation reactions. 14 Notably, a renaissance of the related chemistry has been witnessed and therefore provided a transformative platform for constructing nitrogen-containing heterocycles of different structural skeletons. 15,16 As part of our continuous efforts in exploring new annulation chemistry and potential applications of HZs, 16 we have recently unveiled an unanticipated annulation reaction of 3-acylmethylidene oxindoles 1 with HZs generated in situ from PPh 3 and dialkyl azodicarboxylates 2 ; the annulation reaction features a rare N–N bond cleavage of HZs and also provides a practical synthetic method for complex pyrrolo[4,3,2- de ]quinolinones 3 (Scheme 1A).…”

Strategies and Methods for the Synthesis of 2‐Pyrazolines: Recent Developments (2012–2022)

“…Since then, annulation and condensation reactions of Huisgen zwitterions with electrophiles have been utilized to provide various nitrogen heterocycles, such as pyrroles, furans, [91a] quinolinones, [91b] triazines [91c] thiazolopyridines, [91d] oxadiazoles, [91e] triazolines, [91f] and even acyclic hydrazones [91g] . Annulations with acyl cyanides, [92a] chalcones, [92b] ynones, [92c] and cinnamils [92d] have given access to functionalized 3‐pyrazolines.…”

Metal‐Free K2S2O8‐Mediated Direct Hydrazonation of Methylene in Pyrazoline‐5‐ones

“…[8] In 2019, Zhou's group reported the phosphate-mediated synthesis of N-aryl-N-acyl hydrazones from 1,2-dicarbonyl compounds under mild conditions. [9] The diazo coupling reaction is a common strategy in the preparation of useful intermediates, such as azo dyes and pigments, due to the high reactivity of the diazonium salt. [10] Furthermore, over the last two decades, numerous studies described the synthesis of pyrazoline-5-one 4-hydrazone derivatives through the coupling of diazonium salts with pyrazoline-5-ones (Scheme 1b).…”

“…reported the two‐step synthesis of pyrazol‐5‐one 4‐hydrazones from 3‐methyl‐1‐phenyl‐2‐pyrazoline‐5‐one via bromination and subsequent oxidative hydrazonation process (Scheme 1a) [8] . In 2019, Zhou's group reported the phosphate‐mediated synthesis of N ‐aryl‐ N ‐acyl hydrazones from 1,2‐dicarbonyl compounds under mild conditions [9] . The diazo coupling reaction is a common strategy in the preparation of useful intermediates, such as azo dyes and pigments, due to the high reactivity of the diazonium salt [10] .…”