New and Efficient Protocol for Arylation of Quinones

Abstract

A practical rhodium-mediated arylation of 1,4-quinones has been developed. The corresponding 2-aryl-1,4-quinones were obtained with excellent selectivity and high yields under convenient aerobic reaction conditions.

Key words

arylation - homogeneous catalysis - quinones - rhodium - cross-coupling

References

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12

Typical Coupling Procedure: A glass vial was loaded with [Rh(cod)Cl]₂ (5 mg, 0.01 mmol), Et(CO)Me (5 mL) and COD (35 µL, 0.2 mmol). Then, 1 (137 mg, 1.5 mmol), 2b (264 mg, 1 mmol), and KHSO₄ (137mg, 1 mmol) were sequentially added with stirring. The vial was then equipped with a condenser capped with a PP-cap and was put into a (95 ˚C) hot oil bath to be stirred for 18 h. After that time, the reaction mixture was allowed to cool down to r.t. Products 3 and 5 could be isolated by MPLC on this stage or only 3 after oxidation.
Oxidation: NaIO₄ (213 mg, 1 mmol) and Bu₄NBr (80 mg, 0.25 mmol) were added to the coupling reaction mixture and stirred at r.t. for 3 h. Bu₄NIO₄ (110 mg, 0.25 mmol) was then added. After 21 h of stirring at r.t. solvent was evaporated off, and 3 was chromatographically isolated (SiO₂, 20-400 mesh; hexane-acetone, 6:1) to yield 3 (273 mg, 87%); mp 121-123 ˚C. ^¹H NMR (400 MHz, CDCl₃): δ = 3.90 (s, 3 H), 7.09 (s, 1 H), 7.37-7.40 (m, 2 H), 7.44 (t, J = 7.2 Hz, 1 H), 7.62 (d, J = 8.4 Hz, 1 H), 7.81-7.83 (m, 2 H), 7.86 (d, J = 8.4 Hz, 1 H), 7.98 (d, J = 9.2 Hz, 1 H), 8.19-8.23 (m, 2 H). ^¹³C NMR (100 MHz, CDCl₃): δ = 56.6, 113.1, 116.9, 123.8, 123.9, 126.2, 127.1, 127.2, 128.4, 129.0, 131.1, 132.4, 132.5, 132.6, 133.7, 133.8, 139.3, 147.1, 154.4, 183.8, 185.1. Anal. Calcd for C₂₁H₁₄O₃: C, 80.24; H, 4.49. Found: C, 79.75; H, 4.81.