Synthesis, Table of Contents Synthesis 2021; 53(17): 3057-3064DOI: 10.1055/a-1511-1025 special topic Bond Activation – in Honor of Prof. Shinji Murai Intramolecular Addition of a Dimethylamino C(sp3)–H Bond across C–C Triple Bonds Using IrCl(DTBM-SEGPHOS)(ethylene) Catalyst: Synthesis of Indoles from 2-Alkynyl-N-methylanilines Toshimichi Ohmura ∗ , Kaito Yagi , Takeru Torigoe , Michinori Suginome ∗Recommend Article Abstract Buy Article All articles of this category Abstract Intramolecular addition of a C(sp3)–H bond of the dimethylamino group across the C–C triple bond in 2-alkynyl-N,N-dimethylanilines is effectively catalyzed by a new iridium complex, IrCl(DTBM-SEGPHOS)(C2H4), in mesitylene at 150 °C. The intramolecular C(sp3)–H addition is followed by double-bond isomerization to afford 3-substituted indoles in good to high yields. Key words Key wordsC–H bond activation - addition reaction - cyclization - iridium - indoles Full Text References References For recent reviews, see: 1a Dong Z, Ren Z, Thompson SJ, Xu Y, Dong G. Chem. Rev. 2017; 117: 9333 1b Edwards PM, Schafer LL. Chem. Commun. 2018; 54: 12543 1c Gonnard L, Guérinot A, Cossy J. Tetrahedron 2019; 75: 145 1d Antermite D, Bull JA. Synthesis 2019; 51: 3171 1e Wang H, Gao X, Lv Z, Abdelilah T, Lei A. Chem. Rev. 2019; 119: 6769 1f Fernández DF, Mascareñas JL, López F. Chem. Soc. Rev. 2020; 49: 7378 2a Murai S, Kakiuchi F, Sekine S, Tanaka Y, Kamatani A, Sonoda M, Chatani N. Nature 1993; 366: 529 2b Kakiuchi F, Murai S. Acc. Chem. Res. 2002; 35: 826 3a Xia X.-F, Zhang L.-L, Song X.-R, Niu Y.-N, Liu X.-Y, Liang Y.-M. Chem. Commun. 2013; 49: 1410 3b Gogoi A, Guin S, Rout SK, Patel BK. Org. Lett. 2013; 15: 1802 3c Gogoi A, Modi A, Guin S, Rout SK, Das D, Patel BK. Chem. Commun. 2014; 50: 10445 3d Paladugu S, Mainkar PS, Chandrasekhar S. ACS Omega 2018; 3: 4289 3e Gogoi A, Sau P, Ali W, Guin S, Patel BK. Eur. J. Org. Chem. 2016; 1449 4 Zhang P, Xiao T, Xiong S, Dong X, Zhou L. Org. Lett. 2014; 16: 3264 5a DeBoef B, Pastine SJ, Sames D. J. Am. Chem. Soc. 2004; 126: 6556 5b Ohmura T, Yagi K, Kusaka S, Suginome M. ACS Catal. 2020; 10: 3152 6 Shibata T, Hirashima H, Kasagawa M, Tsuchikama K, Endo K. Synlett 2011; 2171 7a Li Q, Yu Z.-X. J. Am. Chem. Soc. 2010; 132: 4542 7b Li Q, Yu Z.-X. Angew. Chem. Int. Ed. 2011; 50: 2144 7c Cui Q, Liao W, Tian Z.-Y, Li Q, Yu Z.-X. Org. Lett. 2019; 21: 7692 Intramolecular addition of a C(sp3)–H bond α to nitrogen across C–C double bonds to form carbocycles has also been reported: 8a Kubiak R, Prochnow I, Doye S. Angew. Chem. Int. Ed. 2009; 48: 1153 8b Bexrud JA, Eisenberger P, Leitch DC, Payne PR, Schafer LL. J. Am. Chem. Soc. 2009; 131: 2116 8c Prochnow I, Kubiak R, Frey ON, Beckhaus R, Doye S. ChemCatChem 2009; 1: 162 8d Chong E, Schafer LL. Org. Lett. 2013; 15: 6002 8e Dörfler J, Bytyqi B, Hüller S, Mann NM, Brahms C, Schmidtmann M, Doye S. Adv. Synth. Catal. 2015; 357: 2265 9a Torigoe T, Ohmura T, Suginome M. Chem. Eur. J. 2016; 22: 10415 9b Torigoe T, Ohmura T, Suginome M. Angew. Chem. Int. Ed. 2017; 56: 14272 9c Ohmura T, Kusaka S, Torigoe T, Suginome M. Adv. Synth. Catal. 2019; 361: 4448 10 This reaction was slow at 110 °C: 6a was formed in only 33% yield in the reaction of 4a for 24 hours at 110 °C with Ir/L3 (10 mol%). 11 In GC analysis of the reaction mixture, we could not find any significant peaks around the peaks of 4a and 6a. Therefore, we assume that the reaction afforded oligomers of the alkyne. For examples of IrCl(L)2(C2H4), see: 12a Steinert P, Werner H. Organometallics 1994; 13: 2677 12b Werner H, Ortmann DA, Ilg K. Z. Anorg. Allg. Chem. 2000; 626: 2457 12c Carmona D, Ferrer J, Lalaguna E, Lorenzo M, Lahoz FJ, Elipe S, Oro LA. Eur. J. Inorg. Chem. 2002; 259 13 A related 1-octene-coordinated complex IrCl(L3)(1-octene) has been reported: Sevov CS, Hartwig JF. J. Am. Chem. Soc. 2013; 135: 2116 14a Yao B, Wang Q, Zhu J. Angew. Chem. Int. Ed. 2012; 51: 12311 14b Xia X.-F, Wang N, Zhang L.-L, Song X.-R, Liu X.-Y, Liang Y.-M. J. Org. Chem. 2012; 77: 9163 15 The retro-aminoiridation of 8b was slow at 110 °C: 6b was formed in only 7% yield in the reaction of 8b in C6D6 at 110 °C for 12 h. 16 Arthurs MA, Bickerton J, Stobart SR, Wang J. Organometallics 1998; 17: 2743 Supplementary Material Supplementary Material Supporting Information