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TCI Practical Example: The Synthesis of Rubicene through the Scholl Reaction

We are proud to present the synthesis of rubicene from 9,10-diphenylanthracene using DDQ and trifluoromethanesulfonic acid.

Used Chemicals

• DDQ [D1070]
• Trifluoromethanesulfonic Acid (= TfOH) [T0751]
• 9,10-Diphenylanthracene [D1689]
• Dichloromethane

Procedure

Trifluoromethanesulfonic acid (1 mL) was added to a solution of 9,10-diphenylanthracene (200 mg, 0.61 mmol) and DDQ (412 mg, 1.8 mmol, 3.0 eq.) in dichloromethane (19 mL) at 0 °C and the mixture was stirred for 1 hour. The reaction mixture was quenched with sat. NaHCO₃ aq. (20 mL), filtered through celite pad and the residue was washed with dichloromethane (100 mL). The organic layer was washed with sat. NaHCO₃ aq. and dried over anhydrous Na₂SO₄. The solvent was removed under reduced pressure and the residue was purified by column chromatography (hexane:dichloromethane = 0:1 - 1:3 on silica gel) to give rubicene (131 mg, 67%) as a red solid.

Experimenter's Comments

The reaction mixture was monitored by TLC (hexane:dichloromethane = 3:2, Rf = 0.37).
The color of the reaction mixture changed as follows.

• Before adding trifluoromethanesulfonic acid: yellow
• After adding trifluoromethanesulfonic acid: blue
• After quenching with sat. NaHCO₃ aq.: red

Analytical Data

Rubicene

¹H NMR (270 MHz, CDCl₃); δ 8.62 (d, J = 8.6 Hz, 2H), 8.34 (d, J = 7.6 Hz, 2H), 8.04 (d, J = 6.8 Hz, 2H), 7.98 (d, J = 7.0 Hz, 2H), 7.79 (dd, J = 8.6, 6.6 Hz, 2H), 7.45 (td, J = 7.6, 0.8 Hz, 2H), 7.39 (td, J = 7.6, 0.8 Hz, 2H).

Lead Reference

• Facile Synthesis of Rubicenes by Scholl Reaction
  • M. Kawamura, E. Tsurumaki, S. Toyota, Synthesis 2018, 50, 134.