An Efficient Copper-mediated 1,3-Dipolar Cycloaddition of Pyrazolidinone-based Dipoles to Terminal Alkynes to Produce N,N-Bicyclic Pyrazolidinone Derivatives

Abstract

A simple dinuclear copper complex [Cu(®-OH)(tmen)] 2 Cl 2 (tmen = N,N,N¤,N¤-tetramethylethylenediamine) could act as an effective precatalyst for the 1,3-dipolar cycloaddition of pyrazolidinone-based dipoles to terminal alkynes to produce the corresponding N,N-bicyclic pyrazolidinone derivatives.

An Efficient, Ligand‐Free, Heterogeneous Supported Copper Hydroxide Catalyst for the Synthesis of N,N‐Bicyclic Pyrazolidinone Derivatives

“…The products were confirmed by the comparison of their NMR spectra with those of authentic data. [7][8][9]…”

“…Similarly, Fu and co‐workers reported for the first time that the 1,3‐dipolar cycloaddition of azomethine imines to terminal alkynes also proceeds regioselectively in the presence of copper(I) salts and certain nitrogen‐based ligands 7. Although copper‐catalyzed cycloaddition is a powerful method for the synthesis of N , N ‐bicyclic pyrazolidinone derivatives, only a few catalysts have been reported until now; for example, CuI/nitrogen‐based ligands,7 [Cu(μ‐OH)(tmen)] 2 Cl 2 (tmen= N , N , N′ , N′ ‐tetramethylethylenediamine),8 and copper(I)‐exchanged zeolites 9. In addition, these systems have shortcomings such as 1) low turnover frequency (TOF) and turnover number (TON), 2) difficulty in catalyst/product(s) separation and catalyst reuse, and/or 3) indispensability of additives such as stabilizing ligands.…”

“…These values were much higher than those previously reported for the copper-based heterogeneous catalyst of copper(I)-exchanged zeolite (TOF: 4.5 h À1 , TON: 18 at 60 8C). [9] 8 ]toluene (0.27 m, 2 mL) at 40 8C for 1 h under an Ar atmosphere, and the UV/Vis spectrum of the retrieved catalyst was measured. The intensity of the absorption band around 700 nm assignable to the d-d transition of copper(II) species [13] decreased considerably (Figure 1, inset).…”

Cu(I)-catalyzed [3+2] Cycloadditions of tert-Butyl (S)-(3-Oxopent-4- yn-2-yl)carbamate to 1-Benzylidenepyrazole-3-one-derived Azomethine Imines

“…Fu and co-workers reported regioselective and enantioselective copper(I)catalyzed [3+2] coupling of achiral 3-pyrazolidinon-1-azomethine imines with terminal acetylenes to generate optically active pyrazolo[1,2-a]pyrazolone derivatives in 74 -98 % ee [20,21]. Since then, several other examples of catalyzed cycloadditions of 3pyrazolidinone-derived azomethine imines to terminal acetylenes have been published comprising catalysis by CuI [22], di-copper-substituted silicotungstate [23], [Cu(µ-OH)(tmen)] 2 Cl 2 [24], Cu-USY-zeolites [25,26], Cu(OH) x /Al 2 O 3 [27], CuOAc [28], AgN(SiMe 3 ), and CuN(SiMe 3 ) 2 [29]. Moreover, Kobayashi and coworkers also showed that regiochemistry of these reactions can be tuned by the choice of the ligand [29].…”

Synthesis of Functionalized Pyridine‐2,6‐bis(imidazolines) by Ring Transformation of 4‐(Aminomethyl)oxazoline Derivatives

“…Procedures and data for all products 4-7 were in accordance with the literature; [13] Because organoazides are excellent precursors for primary amines, we activated the two primary alcohol functions of compound 6 by sulfonyl ester formation (74 % of product 8, Scheme 3) and converted it by treatment with sodium azide in EtOH by common protocols. Bis-triazole 10 was formed in 81 % yield in the presence, as catalyst, of the commercially available [Cu(μ-OH)(tmeda)] 2 Cl 2 complex, [16] which we had already reported be superior to the standard precatalyst (CuSO 4 , sodium ascorbate). Catalytic hydrogenation of this material proceeded smoothly to give, once again, a unique material (89 % yield) that was mass-spectrometrically and NMRspectroscopically consistent with the constitution of bisaminomethyl compound 1.…”