Ruthenium-Catalyzed Addition of 1,3-Diketones to Terminal Alkynes

Abstract

Ruthenium complex [RuCl₂(CO)₃]₂ catalyzes the addition of 1,3-diketones to terminal alkynes. We observed C-addition with acyclic 1,3-diketones, whereas the use of cyclic 1,3-diketones systematically led to O-addition reactions.

Key words

ruthenium - catalysis - alkynes - 1,3-diketones - vinylation

• References and Notes

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• 10 Reaction of Acyclic Diketones; Typical Procedure for 4-Hydroxy-3-(1-phenylvinyl)-3-pentene-2-one (3a): ^3a Under an atmosphere of argon, acetylacetone (1a; 50 mg, 0.5 mmol) and phenylacetylene (2a; 102 mg, 1 mmol) were added to a screw-cap test tube, then [RuCl₂(CO)₃]₂ (12.8 mg, 0.025 mmol) was added. After sealing the tube, the mixture was stirred by a stirring bar at 70 °C for 5 h. After cooling, the reaction mixture was separated by column chromatography on silica gel (hexane–Et₂O, 98:2), which allowed the isolation of the desired product 3a (59.6 mg, 59%) as a pale-yellow oil; R_f = 0.48 (hexane–Et₂O, 80:20). ¹H NMR (CDCl₃, 500 MHz): δ = 7.31–7.44 (m, 5 H), 5.91 (d, J = 1.0 Hz, 1 H), 5.24 (d, J = 1.0 Hz, 1 H), 1.99 (s, 6 H); ¹³C NMR (CDCl₃, 125 MHz): δ = 191.3 (2C), 143.4, 139.6, 128.7 (2C), 128.1, 125.8 (2C), 118.3, 113.9, 23.5 (2C). Reaction of Cyclic Diketones; Typical Procedure for 3-(1-Phenylvinyloxy)-2-cyclohexenone (5a): Under an atmosphere of argon, 1,3-cyclohexandione (4a; 56 mg, 0.5 mmol) and phenylacetylene (2a; 102 mg, 1 mmol) were placed in a screw-cap test tube and [RuCl₂(CO)₃]₂ (12.8 mg, 0.025 mmol) and benzene (1 mL) were then added. After sealing the tube, the mixture was stirred using a stirring bar at 70 °C for 5 h. After cooling, the reaction mixture was separated by column chromatography on silica gel (hexane–EtOAc, 60:40), which allowed the isolation of the desired product 5a (84.4 mg, 79%) as a pale-yellow oil; R_f = 0.35 (hexane–EtOAc, 60:40). ¹H NMR (CDCl₃, 500 MHz): δ = 7.30–7.42 (m, 4 H), 5.43 (d, J = 1.9 Hz, 1 H), 5.41 (s, 1 H), 4.97 (d, J = 1.9 Hz, 1 H), 2.60 (t, J = 6.4 Hz, 2 H), 2.29 (t, J = 6.4 Hz, 2 H), 2.01 (quint, J = 6.4 Hz, 2 H); ¹³C NMR (CDCl₃, 125 MHz): δ = 199.3, 176.3, 154.7, 133.1, 129.2 (2C), 126.6, 124.9 (2C), 106.3, 101.8, 36.4, 28.1, 21.0; IR (neat): 1613, 1651 cm^–1; MS (EI): m/z (%) = 214 (21) [M]⁺, 186 (21), 158 (26), 103 (100), 77 (57). HRMS (EI): m/z [M]⁺ calcd for C₁₄H₁₄O₂: 214.0994; found: 214.0988.