Directing group assisted rhodium catalyzed meta-C–H alkynylation of arenes Gaurav Prakash ‡ , Sheuli Sasmal , Uttam Dutta ‡ , Ranjini Laskar ‡ , Goutam Kumar Lahiri, Debabrata Maiti Indian Institute of Technology Bombay, India, ‡ These authors contributed equally Transition metal catalyzed C-H activation has evolved as a powerful synthetic tool as it offered a simplified route to incorporate several functional groups by converting inert C-H bond into various carbon-carbon or carbon-heteroatom bonds. 1 The key to success in molecular diversification through C-H bond activation required recognition of a selective C-H bond amongst multiple C-H bonds. 2 Directed C-H activation in this regard provides a unique solution to ensure site-selective C-H activation in a predictable manner. 3 Directing ability of an attached functional group to accommodate the transition metal catalyst to the closest proximity of the desired C-H bond ensured the site-selective C-H functionalization. However, the progress of directed C-H activation is majorly centered around the ortho -C-H activation, which is typically proceeded via five- to seven-membered metallacyclic intermediates. 4 Nevertheless, distal meta -C-H functionalization 5 aided by directing group assistance has recently attracted significant attention. 6 The formation of a large macrocyclic pre-transition state (usually greater than 11-memberered) is the prerequisite criteria to be successful in site-selective distal C-H activation. 7 Despite the success in achieving various meta -selective functionalization utilizing both weak and strong coordinating directing templates, the development was majorly focused on combination of Pd-catalyst and MPAA- ligands (MPAA: mono-protected-amino acid) system. 8 Considering the rapid resurgence in template assisted meta -C-H functionalization under transition metal catalyzed conditions other than Pd-MPAA catalytic system, we are intrigued in developing Rh-catalyzed methods for various meta -C-H functionalization. In order to diversify the scope of distal meta -C-H functionalization, here in we disclosed the first Rh(I) catalyzed meta -C-H alkynylation protocol through inverse Sonogashira coupling reaction. 9 The protocol is compatible with various substrate classes which include phenylacetic acids, hydrocinnamic acids, 2-phenyl benzoic acids, 2-phenyl phenols, benzyl sulfonates and ether-based scaffolds. The post-synthetic modification of meta -alkynylated arenes is also demonstrated through DG-removal as well as functional group interconversion. References 1. L. McMurray, F. O. Hara and M. J. Gaunt, Chem. Soc. Rev. 2011, 40 , 1885–1898. 2. Z. Huang and G. Dong, Acc. Chem. Res. 2017, 50 , 465–471. 3. A. Kapdi and D. Maiti, Strategies for Palladium-Catalyzed Non-directed and Directed C−H Bond Functionalization , Elsevier, Amsterdam, 2017.C. Sambiagio, D. Schonbauer, R. Blieck, T. Dao-Huy, G. Pototschnig, P. Schaaf, T. Wiesinger, M. F. Zia, J. Wencel-Delord, T. Besset, B. U. W. Maes and M. Schnurch, Chem. Soc. Rev . 2018, 47 , 6603–6743. 4. U. Dutta, S. Maiti, T. Bhattacharya and D. Maiti, Science , 2021, 372 , eabd5992. 5. S. K. Sinha, S. Guin, S. Maiti, J. P. Biswas, S. Porey and D. Maiti, Chem. Rev. 2022, 122 ,5682–5841. 6. A. Dey, S. K. Sinha, T. K. Achar and D. Maiti, Angew. Chem. Int. Ed. 2019, 58 , 10820–10843. 7. G. Meng, N. Y. S. Lam, E. L. Lucas, T. G. Saint-Denis, P. Verma, N. Chekshin and J-Q. Yu, J. Am. Chem. Soc. 2020, 142 , 10571–10591. 8. S. Sasmal, G. Prakash, U. Dutta, R. Laskar, G. K. Lahiri and D. Maiti, Chem. Sci., 2022, 13 , 5616.
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