Electrochemical multicomponent synthesis of 4-selanylpyrazoles under catalyst- and chemical-oxidant-free conditions

Abstract

An electrochemical multicomponent reaction was established under catalyst-, chemical-oxidant-free and mild conditions, which provides an eco-friendly and simple protocol for constructing 4-selanylpyrazoles from easily available raw materials with high yields.

A coupling process of electrodialysis with oxime hydrolysis reaction for preparation of hydroxylamine sulfate

“…5 shows the initial cell voltage curve under different current intensities through the ED stack. According to eqn (26), the voltage curve can be tted as a function (the green curve in Fig. 5a): U total ¼ 1.94 + 0.23 log I + 0.82I.…”

“…Electrodialysis (ED) is an extraordinarily mature and effective separation technique widely used in varieties of elds, such as seawater desalination, 15,16 wastewater treatment, [17][18][19] food, 20,21 and pharmaceutical [22][23][24][25][26] industries. The keys to isolation and aggregation of target ions or molecules are the selective permeability of ion exchange membranes (IEMs) and the directional migration of ions under an electric eld.…”

Facile One-Pot Preparation of 5-Substituted 4-Iodo-1-tosylpyrazoles from N-Propargyl-N′-tosylhydrazines through Iodocyclization

“…Recent examples of pyrazoles prepared in the absence of transition metals are as follows: 4 1-aryl-4-iodopyrazoles­ from the reaction of N -aryl- N ′-(α-alkynyl)­hydrazones with molecular iodine (I 2 ) and NaHCO 3 ; 4a 3-substituted pyrazoles from the reaction of propargylamines with m CPBA and then with hydrazines; 4b 3,5-disubstituted 1-arylpyrazoles from the reaction of α,β-unsaturated aldehydes with arylhydrazines and I 2 ; 4c 1-arylpyrazole-4-carboxylate esters from the reaction of α-[( tert -butoxycarbonyl)oxy]methylacrylate esters with N -arylazosulfones and Bu 3 P; 4d 5-amino-3-aryl-1-tosylpyrazoles from the reaction of N -tosylhydrazones with isocyanides, t BuOOH, and I 2 ; 4e ethyl 1-aryl-5-(acetylmethyl)pyrazole-4-carboxylates from the reaction of ethyl acetoacetate with arylhydrazines and NaOEt; 4f 1-aryl-5-hydroxy-4-thioarylpyrazoles from the reaction of arylhydrazines with ethyl acetoacetate, arenethiols, and I 2 ; 4g 1,5-diaryl-4-iodo-3-(trifluoromethyl)pyrazoles from the reaction of N -arylhydrazones of arylethynyl trifluoromethyl ketones with I 2 ; 4h 1,4-bis(arenesulfonyl)pyrazoles from the reaction of β-amino-α,β-unsaturated ketones­ with arenesulfonylhydrazines, t BuOOH, and I 2 ; 4i 5-amino-1-arylpyrazoles from the reaction of 3-aminocrotonitrile with arylhydrazine and 1 M HCl under microwave irradiation; 4j 1,3-diarylpyrazoles from the reaction of hydrazonyl chlorides with benzyl vinyl ether and Et 3 N; 4k 1,3-di­aryl-5-(bromomethyl)pyrazoles from the reaction of hydrazonyl chlorides with dimethyl propargylsulfonium and K 2 CO 3 ; 4l 1,4-bis(arenesulfonyl)pyrazoles from the reaction of 1,3-diketones with arenesulfonylhydrazines, arenesulfinate salts, and I 2 ; 4m and 1-aryl-4-selenoarylpyrazoles from the reaction of 1,3-diketones with arylhydrazines and diaryl diselenides by electrochemical method. 4n Examples of pyrazoles prepared in the presence of transition metals are as follows: 5 1-benzylpyrazole-4-carboxylates from the reaction of 2,3-allenoates with benzylamine in the presence of Cu(OAc) 2 ; 5a 1,4-diarylpyrazoles from the reaction of N -arylsydnone with terminal alkynes in the presence of silica-supported Cu(OAc) 2 ; 5b 1,5-diaryl-3-(trifluoromethyl)pyrazoles from the reaction of alkynyl trifluoromethyl ketones and arylhydrazines in the presence of AgOTf; 5c 1-aryl-3,5-dimethylpyrazoles from the reaction of arylhydrazines with Cu(acac) 2 under microwave irradiation; 5d 1,3,5-triaryl-4-selenophenylpyrazoles from the reaction of chalcones with arylhydrazines in the presence of CuBr; 5e 1-tosyl­pyrazole-4-boronate esters from the reaction of N -tosyl-(α-alkynyl)hydrazones with B -chlorocatechol...…”

Non-metal-mediated N-oxyl radical (TEMPO)-induced acceptorless dehydrogenation of N-heterocycles via electrocatalysis

“… 11 In general, the electrochemical reaction with electrons as the oxidizing/reducing agent can be performed at room temperature without the use of chemical oxidants, which makes it safe and low cost. 12 Recently, Gong's group has developed an electrochemical dehydrogenation method for synthesis of quinazolin-4(3 H )-ones under metal-free and oxidant-free conditions by combining acid-catalyzed annulation and TEMPO as the catalyst. 11 b Inspired by the Gong work, we envisaged electrocatalysis combined with nitroxyl radicals as a new strategy to direct catalytic acceptorless dehydrogenation of N-heterocycles under neutral conditions ( Scheme 1 ).…”