01115nas a2200169 4500008004100000022001400041245011300055210006900168260011000237300001600347490000600363520038600369100001800755700002100773700002000794856013100814 2015 eng d a2046-206900aMetal-free regioselective C-3 acetoxylation of N-substituted indoles: crucial impact of nitrogen-substituent0 aMetalfree regioselective C3 acetoxylation of Nsubstituted indole aTHOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLANDbROYAL SOC CHEMISTRYcJUN a57472-574810 v53 a

A metal-free method for the regioselective C-3 acetoxylation of the N-substituted indoles with PhI(OAc)(2) is described under mild reaction conditions. This method tolerates a broad range of functional groups with moderate to good yields. The pi-electron-deficient aryl-substituents on the N-atom of indoles and the acidic reaction medium remarkably favor C-3 acetoxylation.

1 aSoni, Vineeta1 aPatel, Ulhas, N.1 aPunji, Benudhar uhttps://library.ncl.res.in/content/metal-free-regioselective-c-3-acetoxylation-n-substituted-indoles-crucial-impact-nitrogen-002240nas a2200205 4500008004100000022001400041245009000055210006900145260000800214300001400222490000700236520155700243100002401800700001801824700002101842700002401863700001701887700002001904856011001924 2018 eng d a0276-733300aMechanism of nickel(II)-catalyzed C(2)-H alkynylation of indoles with alkynyl bromide0 aMechanism of nickelIIcatalyzed C2H alkynylation of indoles with  cJUL a2037-20450 v373 a

The nickel system (THF)(2)NiBr2/phen has recently been shown as an efficient catalyst for the C-H bond alkynylation of diverse heteroarenes with (triisopropylsilyl)alkynyl bromide via monodentate chelation assistance. Herein, we report an extensive mechanistic investigation for the direct alkynylation of indoles involving the well-defined nickel catalyst, which features a coordinative insertion pathway of alkynyl bromide with the Ni(II) catalyst. Catalytic relevant nickel complexes, (phen)NiCl2 (5), (phen)(2)NiCl2 (6) and [(phen)(3)Ni].NiCl4 (7) were isolated, and the complexes 6 and 7 were structurally characterized. Well-defined complexes were as competent as the in situ generated catalyst system (THF)(2)NiBr2/phen for the alkynylation of indoles. Various controlled studies and reactivity experiments were performed to understand the probable pathway for the alkynylation reaction. Kinetics analysis highlights that the complex (phen)NiX2 acts as a precatalyst, and the involvement of substrate indole and LiO'Bu are essential for the generation of the active catalyst. Deuterium labeling and kinetic studies suggest that the process involving C-H cleavage and carbo-nickelation of indole is a crucial rate influencing step. Reactivity study of various alkynyl compounds with nickel-species highlights a migratory insertion route for the reaction. DFT calculations firmly support the experimental findings and suggest the coordinative insertion pathway of alkynyl bromide rather than oxidative addition toward the nickel(II) center.

1 aKhake, Shrikant, M.1 aJain, Shailja1 aPatel, Ulhas, N.1 aGonnade, Rajesh, G.1 aVanka, Kumar1 aPunji, Benudhar uhttps://library.ncl.res.in/content/mechanism-nickelii-catalyzed-c2-h-alkynylation-indoles-alkynyl-bromide02045nas a2200205 4500008004100000022001400041245010400055210006900159260000800228300001400236490000700250520133400257100002101591700001801612700002201630700002401652700001701676700002001693856012601713 2018 eng d a0276-733300aMechanistic aspects of pincer nickel(II)-catalyzed C-H bond alkylation of azoles with alkyl halides0 aMechanistic aspects of pincer nickelIIcatalyzed CH bond alkylati cMAR a1017-10250 v373 a

The quinolinyl-based pincer nickel complex, kappa(N),kappa(N),kappa(N)-{C9H6N-(mu-N)-C6H4-NMe2}NiCl [((NNNMe2)-N-Q)-NiCl; (1)] has recently been demonstrated to be an efficient and robust catalyst for the alkylation of azoles with alkyl halides under copper-free conditions. Herein, we report the detailed mechanistic investigation for the alkylation of azoles catalyzed by ((NNNMe2)-N-Q)NiCl (1), which highlights an iodine atom transfer (IAT) mechanism for the reaction involving a Ni-II/Ni-III process. Deuterium labeling experiments indicate reversible cleavage of the benzothiazole C-H bond, and kinetic studies underline a fractional negative rate order with the substrate benzothiazole. The involvement of an alkyl radical during the alkylation is validated by radical clock and external additive experiments. An active intermediate species ((NNNMe2)-N-Q)Ni(benzothiazolyl) (5a) has been isolated and structurally characterized. The complex ((NNNMe2)-N-Q)Ni(benzothiazoly1) (5a) is found to be the resting state of catalyst 1. Kinetic analysis of electronically different intermediates suggests that the step involving the reaction of 5a with alkyl iodide is crucial and a rate-influencing step. DFT calculations strongly support the experimental findings and corroborate an IAT process for the alkylation reaction.

1 aPatel, Ulhas, N.1 aJain, Shailja1 aPandey, Dilip, K.1 aGonnade, Rajesh, G.1 aVanka, Kumar1 aPunji, Benudhar uhttps://library.ncl.res.in/content/mechanistic-aspects-pincer-nickelii-catalyzed-c-h-bond-alkylation-azoles-alkyl-halides