Synthesis of Tetraarylmethanes by the Triflic Acid-Promoted Formal Cross-Dehydrogenative Coupling of Triarylmethanes with Arenes

Dedicated to Professor Victor Snieckus, colleague, mentor, and friend on the occasion of his 80th birthday.

Abstract

The formal cross-dehydrogenative coupling of triarylmethanes with arenes promoted by triflic acid and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone is described. This method provides a variety of tetraarylmethane derivatives in good to excellent yields from triarylmethanes that can be readily prepared by our previous methods. Control experiments suggest a possible catalytic cycle involving the generation of a trityl cation intermediate followed by nucleophilic addition of the arene.

Key words

cross-coupling - dehydrogenation - tetraarylmethanes - triarylmethanes - arylation - organocatalysis

• References and Notes


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• 18 1-Methoxy-4-tritylbenzene (3aa); Typical Procedure A 10-mL sealable reaction tube equipped with a magnetic stirring bar and a septum was evacuated, flame-dried under vacuum, cooled to r.t., and backfilled with argon. The tube was then charged with Ph₃CH (1a; 24.4 mg, 0.1 mmol) and DDQ (45.4 mg, 0.2 mmol, 2 equiv) under a constant stream of argon. The tub was evacuated for 5 min and refilled with argon. This cycle was repeated twice more. DCE (0.3 mL), TfOH (0.9 μL, 0.01 mmol, 10 mol%), and anisole 2a (51 μL, 0.5 mmol, 5 equiv) were added, and the vessel was sealed. The mixture was stirred at 100 °C for 6 h then cooled to r.t. EtOAc (~5 mL) was added, and the solution was passed through a pad of Celite with copious washings with EtOAc. The solvent was evaporated under reduced pressure to give a crude product that was purified by preparative TLC (hexane–EtOAc, 50:1) to give a white solid; yield: 25.9 mg (74%). ¹H NMR (400 MHz, CDCl₃): δ = 3.78 (s, 3 H), 6.80 (dm, J = 9.2 Hz, 2 H), 6.80 (dm, J = 9.2 Hz, 2 H), 7.16–7.26 (m, 15 H). ¹³C NMR (150 MHz, CDCl₃): δ = 55.2, 64.3, 112.7, 125.8, 127.4, 131.1, 132.2, 139.0, 147.0, 157.5. HRMS (DART): m/z calcd for C₂₆H₂₂O: 350.1671; found: 350.1663.