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TCI Practical Example: The Intermolecular [2+2] Cycloaddition Catalyzed by a Photoredox Catalyst

We are proud to present the [2+2] photocycloaddition reaction between an extended enoate and an olefin catalyzed by Ru(phen)₃(PF₆)₂.

Used Chemicals

• Ethyl (E)-4-(4-Fluorophenyl)-2-oxobut-3-enoate (1)
• 1,1-Diphenylethylene [D0886]
• Tris(1,10-phenanthroline)ruthenium(II) Bis(hexafluorophosphate) (= Ru(phen)₃(PF₆)₂) [T3208]
• Acetone

Procedure

A 3-neck round bottom flask was charged with 1 (0.1 g, 0.5 mmol, 1 eq.), 1,1-diphenylethylene (0.2 g, 1 mmol, 2 eq.), Ru(phen)₃(PF₆)₂ (0.009 g, 0.01 mmol, 2 mol%), degassed acetone (12.5 mL) at rt under N₂. The mixture was placed at a distance of 2-3 cm from Blue LED lamp with a cooling fan. The reaction mixture was stirred at rt under visible light irradiation. After 19 hours of irradiation, the solvent was removed in vacuo, giving crude as a blown oil (0.32 g). The crude was purified by silica gel column chromatography (hexane:ethyl acetate = 10:1, Rf = 0.57) to give compound 2 as a colorless sticky solid (0.12 g, Y. 60%)

Experimenter’s Comments

• Acetone was degassed with nitrogen for 30 min before use.
• Irradiation of visible light was performed with Kessil A160WE Tuna Blue 40W x 2.
• Temperature of the reaction mixture was maintained at rt by a cooling fan.
• The reaction mixture was monitored by ¹H NMR and TLC.

Analytical Data

Compound 2

¹H NMR (400 MHz, CDCl₃); δ 7.33−7.27 (m, 4H), 7.20−7.12 (m, 4H), 7.00−6.98 (m, 2H), 6.83−6.78 (m, 4H), 4.54 (d, J = 9.2 Hz, 1H), 4.28−4.01 (m, 3H), 3.49-3.36 (m, 1H), 2.66 (t, J = 10.5 Hz, 1H),1.20 (t, J = 7.3 Hz, 3H).

¹³C NMR (101 MHz, CDCl₃); δ 193.4, 161.8 (d, J_C‑F = 247.49 Hz), 161.3, 161.0, 150.0, 140.8, 133.8 (d, J_C‑F = 2.9 Hz), 130.3 (d, J_C‑F = 7.7 Hz), 128.5, 128.4, 128.0, 126.4, 126.1, 114.6 (d, J_C‑F = 21.1 Hz), 62.5, 53.6, 52.9, 44.0, 33.7, 14.5.

¹⁹F NMR (376 MHz, CDCl₃); δ -116.39 (s, 1F).

Lead Reference

• Visible-Light-Triggered Selective Intermolecular [2+2] Cycloaddition of Extended Enones: 2‑Oxo-3-enoates and 2,4-Dien-1-ones with Olefins
• L.-M. Zhao, T. Lei, R.-Z. Liao, H. Xiao, B. Chen, V. Ramamurthy, C.-H. Tung, L.-Z. Wu, J. Org. Chem. 2019, 84, 9257.

Other References

• Direct Synthesis of β,γ-Unsaturated α-Keto Esters from Aldehydes and Pyruvates
• J. K. Mansaray, J. Sun, S. Huang, W. Yao, Synlett 2019, 30, 809.