Solvent‐Free Ruthenium(II)‐Catalyzed C–H Activation: Synthesis of Alkenylarylpyrazole Derivatives

Abstract

Keywords: C-H activation / Ruthenium / Alkenylation / Nitrogen heterocyclesThe Ru II carboxylate complex Ru(MesCO 2 ) 2 (p-cymene) (Mes = mesityl) was found to be an efficient catalyst for the direct dehydrogenative alkenylation of N-arylpyrazoles by using styrenes and acrylates in the presence of Cu(OAc) 2 ·H 2 O in open air. The highly step-economical C-H bond functionalization process is characterized by a wide substrate scope and significant chemoselectivity, which allowed direct alkenylation to be performed either under solvent-free reaction con-

Recent Advances in C–H Bond Functionalization with Ruthenium-Based Catalysts

“…The reaction produced only C-3 alkylated product when [RuCl 2 (p-cymene)] 2 was used without a base,which is comparable to the yield of C-3 alkenylated product in the presence of K 2 CO 3 (Scheme 44). [111]. Recently, they also demonstrated the alkenylation of 1-phenylpyrazole with acrylate using a ruthenium(II) bipyridine complex, [Ru(MesCO 2 )(L)(p-cymene)] + , in the presence of Cu(OAc) 2 •H 2 O in ethanol at 80 • C, predominantly producing a monoalkenylated product (Scheme 45b) [112].…”

Ruthenium-bipyridine complex catalyzed C–H alkenylation of arylpyrazole derivatives

“…Purification by column chromatography (Hexane/EtOAc: 90/10) yielded 1b. 1 15 : The general procedure was followed using 4-fluoro phenylpyrazole (87 mg, 0.5 mmol) and butyl acrylate (0.049 mL, 0.55 mmol) in ethanol. Purification by column chromatography (Hexane/EtOAc: 90/10) yielded 1c.…”

“…Purification by column chromatography (Hexane/EtOAc: 90/10) yielded 1c. 1 15 : The general procedure was followed using 4-methoxy phenylpyrazoles (87 mg, 0.5 mmol) and butyl acrylate (0.147 mL, 1.5 mmol) in ethanol under sealed tube conditions for more than 20 h. Purification by column chromatography (petroleum ether/Et 2 O : 90/10) yielded 1g. 1 15 : The general procedure was followed using 4,4 -dimethylphenyloxazoline (66 µL, 0.5 mmol) and butylacrylate (0.07 mL, 0.55 mmol) in ethanol for 6 h. Purification by column chromatography (Hexane/EtOAc: 70/30) yielded 1i.…”

“…1 15 : The general procedure was followed using 4-methoxy phenylpyrazoles (87 mg, 0.5 mmol) and butyl acrylate (0.147 mL, 1.5 mmol) in ethanol under sealed tube conditions for more than 20 h. Purification by column chromatography (petroleum ether/Et 2 O : 90/10) yielded 1g. 1 15 : The general procedure was followed using 4,4 -dimethylphenyloxazoline (66 µL, 0.5 mmol) and butylacrylate (0.07 mL, 0.55 mmol) in ethanol for 6 h. Purification by column chromatography (Hexane/EtOAc: 70/30) yielded 1i. 1 15 : The general procedure was followed using 1-(4-(1H-pyrazol-1-yl)phenyl)ethanone (93 mg, 0.5 mmol) and butyl acrylate (0.147 mL, 1.5 mmol) in ethanol under sealed tube conditions for more than 20 h. Purification by column chromatography (Hexane/ EtOAc: 70/30) yielded 1j.…”

“…5 Use of [RuH 2 (CO)(PPh 3 ) 3 ] as catalyst in the C-H-activated alkenylation of arenes with alkynes was first pioneered by Kakiuchi and Trost, 6 following which several reports on different transition metals like ruthenium, 7 rhodium, 8 palladium, 9 iridium, 10 rhenium, 11 nickel 12 and cobalt 13 have been successfully applied in C-H bond activation. One of the most powerful strategies for the dissociation and functionalization of C-H bonds is the chelation-assisted C-H activation approach that allows several directing groups like pyridines, 14 pyrazoles, 15 nitroso, 16 sulfoximine, 17 P=O bonds 18 and unsaturated C-C bonds 19 to assist the selective C-H bond functionalization.…”