Experimental study demonstrates regioselective cobalt-catalyzed C(4)–H functionalization of 3-pivaloyl indole using alkynes, indicating novel reaction pathways mediated by in situ water formation.
Unique reactivity of diphenylacetylene has been uncovered through weak chelation-assisted cobalt-catalyzed regioselective C(4)–H activation of 3-pivolyl indole. α-Hydroxy ketone and α,β-unsaturated ketone derivatives have been synthesized in good yields from indole and alkynes. Notably, the indole C(4)–H-functionalized α,β-unsaturated ketone product was obtained with high stereo- and regioselectivity simply by changing the coupling partner from symmetrical alkynes to unsymmetrical aromatic-aliphatic alkynes. Most importantly, trifluoroethanol acts as a sole source of water for this conversion. Quantitative detection of bis(2,2,2-trifluoroethyl) ether from dry trifluoroethanol through 19 F NMR and LCMS studies indirectly confirms the in situ formation of water. A six-membered cobaltacycle intermediate was detected in HRMS, and also, this was further confirmed by the quantum mechanical calculations, which accounts for the highly regioselective C(4)–H functionalization.
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Banjare et al. (2021) studied this question.
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