Aerobic Oxidation of Alkyl 2-Phenylhydrazinecarboxylates Catalyzed by CuCl and DMAP

Abstract

Recently, various fruitful organic reactions such as a catalytic Mitsunobu reaction were reported by virtue of alkyl 2-phenylazocarboxylates, however, the synthesis of alkyl 2-phenylazocarboxylates largely depended on the stoichiometric use of toxic oxidants. In this manuscript, an environment-friendly aerobic oxidative transformation of alkyl 2-phenylhydrazinecarboxylates to alkyl 2-phenylazocarboxylates is disclosed. The use of CuCl and DMAP system efficiently catalyzed the aerobic oxidation of alkyl 2-phenylhydrazinecarboxylates under mild conditions. The reaction rate of the present Cu-catalysis was much faster than that of the previously reported Fe-catalysis, and a variety of azo products were synthesized within 3 h. The present protocol was effective on larger scale. It was observed that the produced azo compound could undergo various reactions without isolation through one-pot sequential protocols.

Synthesis of Cinnolines and Cinnolinium Salt Derivatives by Rh(III)-Catalyzed Cascade Oxidative Coupling/Cyclization Reactions

“…First, Boc-phenylhydrazine was treated without diphenylacetylene under the optimal conditions, and ( E )- tert -butyl 2-phenyldiazenecarboxylate ( 5b) was isolated in 18% yield (Scheme , eq 1). In the literature, there are many reports on the conversion of N ′-phenylhydrazide to the azo compounds under mild oxidation conditions . Therefore, we inferred that the Boc-phenylhydrazine may be converted to the corresponding azo compounds first in the reaction system.…”

Systematic Evaluation of 2-Arylazocarboxylates and 2-Arylazocarboxamides as Mitsunobu Reagents

“…This feature was applicable to easy and scalable recovery of the reagents. The emergence of recyclable azo reagents in the Mitsunobu reaction shall inspire development of new protocols for the parent hydrazine oxidations …”

“…The emergence of recyclable azo reagents in the Mitsunobu reaction shall inspire development of new protocols for the parent hydrazine oxidations. 35 Most of the 2-arylazocarboxylates and 2-arylazocarboxamides were stable for more than a few months under ambient conditions. SC-DSC analyses of representative azo reagents revealed considerably higher exothermic decomposition points as compared to the typical Mitsunobu azo reagents such as DEAD.…”

Oxidative Dehydrogenation of Hydrazobenzenes toward Azo Compounds Catalyzed by tert-Butyl Nitrite in EtOH

“…Azo compounds, a class of prominent compounds containing a NN unsaturated bond, are versatile synthetic building blocks in synthesis as well as pervasive motifs in related bioactive natural products, pharmaceuticals, functional materials (e.g., dyes, pigments, indicators, photochemical switches, chemosensors, food additives, and polymers), and radical-reaction initiators . As a result, considerable efforts have been dedicated to the development of efficient, sustainable methods for azo compound synthesis. − ,,, Among them, dehydrogenation of the NH–NH bonds in hydrazines represents the most efficient and straightforward method for these purposes. − ,,, Traditional approaches usually employ an excess amount of strong oxidants (e.g., MnO 2 , KMnO 4 , and HgO) to oxidative dehydrogenation of hydrazobenzenes for accessing azo compounds (Scheme a) . However, these transformations suffer from a limited substrate scope, occurrence of unwanted side reactions, and discharge of large quantities of waste.…”