Ruthenium(II)-Catalyzed C–H Alkynylation of Heterocycles under Chelation Assistance

Abstract

An efficient ruthenium(II)-catalyzed, chelation-assisted C–H alkynylation of heterocycles is described using hypervalent iodine–alkyne as an alkynylating reagent. This reaction proceeds smoothly under mild conditions with high regioselectivity and good functional group tolerance, delivering the desired alkynylated indoles, thiophene, furan, and pyrrole in high yields.

Key words

ruthenium - alkynylation - hypervalent iodine–alkyne - ­chelation - heterocycles.

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• 14 1-(Pyrimidin-2-yl)-2-[(triisopropylsilyl)ethynyl]-1H-indole (3a) – Typical Procedure 1-(Pyrimidin-2-yl)-1H-indole (1a, 0.1 mmol, 1.0 equiv), hypervalent iodine–alkyne 2a (0.12 mmol, 1.2 equiv), [Ru(cymene)Cl₂]₂ (5 mol %), AgSbF₆ (0.02 mmol, 20 mol%), NaOAc (0.1 mmol, 1.0 equiv), and 1,2-DCE (1 mL) were charged into a pressure tube under argon. The reaction mixture was stirred for 24 h at 80 °C under Ar atmosphere, and then the mixture was cooled to room temperature. The solvent was removed under reduced pressure, and the residue was purified by silica gel chromatography using EtOAc/PE to afford the alkynylation product 3a. ¹H NMR (400 MHz, CDCl₃): δ = 8.79 (d, J = 4.8 Hz, 2 H), 8.28 (d, J = 7.7 Hz, 1 H), 7.57 (d, J =7.7 Hz, 1 H), 7.34–7.29 (m, 1 H), 7.25–7.19 (m, 1 H), 7.17 (t, J = 4.8 Hz, 1 H), 7.08 (s, 1 H), 1.14 (s, 21 H). ¹³C NMR (100 MHz, CDCl₃ ): δ = 158.1, 157.4, 136.2, 128.6, 124.8, 122.4, 121.0, 120.7, 117.5, 115.7, 114.1, 98.8, 97.9, 18.7, 11.4.