Copper-Promoted Aerobic Oxidative [3+2] Cycloaddition Reactions of N,N-Disubstituted Hydrazines with Alkynoates: Access to Substituted Pyrazoles

Abstract

A copper-promoted aerobic oxidative [3+2] cycloaddition reaction for the synthesis of various substituted pyrazoles from N,N-disubstituted hydrazines with alkynoates in the presence of bases is developed. This work involves a direct C(sp3)–H functionalization and the formation of new C–C/C–N bonds. In this strategy, inexpensive and easily available Cu2O serves as the promoter and air acts as the green oxidant. The reaction exhibits the advantages of high atom and step economy, high regioselectivity, and easy operation.

Palladium–Copper-Catalyzed Oxidative Intermolecular [2 + 2 + 2] Coupling–Annulation: Regioselective Synthesis of Multiaryl-Substituted Benzenes

“…Thin layer chromatography (TLC) was used on commercially available 100–400 mesh silica gel plates. Alkynoates ( 2b – x ) were prepared according to our previous report . Other alkynoates were obtained from Innochem (Beijing) Technology Co., Ltd. of China.…”

“…Alkynoates (2b−x) were prepared according to our previous report. 28 Other alkynoates were obtained from Innochem (Beijing) Technology Co., Ltd. of China. Unless otherwise stated, all purchased chemicals were used without further purification.…”

Copper-Catalyzed Domino-Double Annulation of o-Aminobenzamides with 2-Iodoisothiocyanates for the Synthesis of 12H-Benzo[4,5]thiazolo[2,3-b]quinazolin-12-ones

“…Therefore, the development of concise and efficient synthetic routes toward 12 H -benzo­[4,5]­thiazolo­[2,3- b ]­quinazolin-12-ones is still highly desirable. In a continuation of our research interests in developing new synthetic methodologies for constructing valuable N -heterocyclic compounds, herein we describe a convenient and efficient copper-catalyzed domino-double annulation of o -aminobenzamides and 2-iodoisothiocyanates for the synthesis of tetracyclic fused 12 H -benzo­[4,5]­thiazolo­[2,3- b ]­quinazolin-12-ones in moderate to good yields (Scheme f). The reaction was performed without the addition of ligands, bases, and external oxidants, which involves a C–N bond cleavage and the formation of a C–N/C-S bond in one step.…”

Metal‐Free [2+3] Dipolar Cycloaddition/Denitration Cascade between Nitroalkenes and α‐Diazoesters: Regioselective Access to Functionalized NH−Pyrazoles

“…Recently, a silver‐catalyzed decarboxylative cyclization was developed for the synthesis of pyrazoles from 1,2‐diaza‐1,3‐dienes and α‐ketoacids (Scheme 1c) [13c] . Very recently, copper‐promoted aerobic oxidative [3+2] cycloaddition reaction for the synthesis of pyrazoles from N,N‐disubstituted hydrazines with alkynoates has been devised (Scheme 1d) [13d] . Xie and co‐workers [13e] also reported an efficient method for the synthesis of functionalized pyrazoles via tandem reaction of nitroalkenes with ethyl diazoacetate.…”