Catalyst-Free Radical Dearomatization of Phenols with Aryldiazonium Tetrafluoroborates and DABCO·(SO₂)₂

Abstract

A catalyst-free, three-component dearomatization of phenols with aryldiazonium tetrafluoroborates and DABCO·(SO₂)₂ has been developed for the synthesis of 4-(arylsulfonyl)cyclohex-2,5-dien-1-one scaffolds. This method offers mild reaction conditions and high step efficiency, providing a green and efficient strategy for the dearomatization of phenols. Mechanistic studies indicated that this transformation relies on a tandem radical sulfur dioxide insertion process.

Key words

dearomatization - phenols - sulfur dioxide insertion - catalyst-free reaction - aryldiazonium tetrafluoroborates - arylsulfonylcyclohexadienones

Publication History

Received: 17 December 2024

Accepted after revision: 21 January 2025

Article published online:
04 March 2025

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• 45 4-(Arylsulfonyl)cyclohex-2,5-dien-1-ones 3a–w: General Procedure The appropriate phenol 1 (0.2 mmol), aryldiazonium salt 2 (0.4 mmol), and DABSO (72 mg, 0.3 mmol) were added to a 10 mL oven-dried reaction vial equipped with a magnetic stirrer bar. The reaction vessel was sealed with a rubber stopper, evacuated, and refilled three times with N₂. DMF (2.0 mL) was then added from a syringe, and the resulting mixture was stirred at 40 °C for 12 h until the reaction was complete (TLC). The mixture was diluted with H₂O (10 mL) and extracted with EtOAc (3 × 15 mL). The combined organic phase was concentrated, and the residue was purified by flash chromatography (silica gel, PE–EtOAc). 2,6-Di-tert-butyl-4-methyl-4-tosylcyclohexa-2,5-dien-1-one (3a) Prepared according to the general procedure and purified by flash column chromatography [silica gel, PE–EtOAc (15:1 to 10:1)] to give a white solid; yield: 63 mg (84%); mp 142–143 ℃; R_f = 0.4. ¹H NMR (400 MHz, CDCl₃): δ = 7.50 (d, J = 7.0 Hz, 2 H), 7.17 (d, J = 8.1 Hz, 2 H), 6.63 (s, 2 H), 2.35 (s, 3 H), 1.80 (s, 3 H), 1.09 (s, 18 H). ¹³C NMR (101 MHz, CDCl₃): δ = 183.7, 151.2, 145.3, 135.7, 130.6, 130.3, 128.8, 65.8, 35.2, 29.0, 21.6, 18.5. HRMS (ESI, ion trap): m/z [M + H]⁺ calcd for C₂₂H₃₁O₃S: 375.1989; found: 375.1988.