Copper(ii)-catalyzed coupling reaction: an efficient and regioselective approach to N′,N′-diaryl acylhydrazines

Abstract

Using N'-aryl acylhydrazines as aryl donors, a novel copper(ii)-catalyzed homo-coupling reaction of N'-aryl acylhydrazines has been developed for the synthesis of N',N'-diaryl acylhydrazines. We also provided a complementary procedure for the preparation of unsymmetrical diaryl acylhydrazines via cross-coupling reaction. These protocols featured mild reaction conditions, wide functional group tolerance and highly regioselective products. Control experiments indicated that this kind of coupling reaction might undergo a transient acyl diazene intermediate.

Palladium‐Catalyzed Regioselective C‐2 Arylation of Benzofurans with N′‐Acyl Arylhydrazines

“…of TEMPO were optimal for this C‐2 arylation reaction (entries 20–23). Additionally, the reaction could also work under an argon atmosphere albeit with a much lower yield (entry 24); a similar result was presented in our previous work and the reaction may occur via a different mechanism in the absence of oxygen , …”

“…Based on these experiments and the literature,[7a], [11a], , , we proposed a possible mechanism for the Pd‐catalyzed arylation reaction (Figure ). N′ ‐Acyl arylhydrazine ( A ) was oxidized by the Pd II species to give diazene intermediate B .…”

“…To the best of our knowledge, there is no report on the arylation of benzofurans using arylhydrazines as the aryl source. Our previous work demonstrated that N′ ‐acyl arylhydrazine is an efficient coupling partner for the arylation of arylhydrazines and olefins . As we continued exploring the reaction profiles of N′ ‐acyl arylhydrazines, we envisioned that the direct arylation of benzofurans via C–H functionalization using N′ ‐acyl arylhydrazines can be performed regioselectively under transition‐metal catalyzed conditions.…”

Sterically Shielded Stable Carbenes and Biscarbenes of the 1,2,4‐Triazole Series: A New Method for the Preparation of 1,3,4‐Triaryl‐1,2,4‐triazol‐5‐ylidenes

“…The acylation reaction of phenylhydrazine can also be carried out without the use of acid halides; in particular under the action to phenylhydrazine of benzoic anhydride or benzoic acid in the presence of carbodiimides or other condensing agents (see, for example,). In the present paper a preparatory one‐reactor method was used for obtaining 2‐benzoyl‐1‐formylhydrazine from phenylhydrazine and benzoyl chloride in dimethoxyethane at 0–5 °C followed by further refluxing in formic acid.…”

Synthesis of N‐Aryl‐ and N‐Alkenylhydrazides through C(sp2)−N Bond Construction

“…Lu developed a regioselective protocol to approach N ’, N ’‐diaryl acylhydrazines 111 / 142 through copper‐catalyzed homo‐coupling of N ’‐aryl acylhydrazines at ambient temperature (Scheme 43). [74a] In this process, N ‐acyl‐ N ’‐arylhydrazines 34 or 35 served not only as a hydrazine source but also as an aryl donor. Aliphatic acyl, aromatic acyl, trifluoroacetyl, and alkoxycarbonyl substituted hydrazine worked smoothly under standard conditions.…”