Transition‐Metal‐Free C(sp2)–C(sp2) Cross‐Coupling of Diazo Quinones with Catechol Boronic Esters

• Published in: Angewandte Chemie International Edition Vol. 59; no. 37; pp. 16202 - 16208
• Main Authors: Wu, Kai, Wu, Liang‐Liang, Zhou, Cong‐Ying, Che, Chi‐Ming
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 07.09.2020; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: boronic esters; C(sp2)−C(sp2) bond; Catechol; Chemistry; Chemistry, Multidisciplinary; Cross coupling; cross-coupling reactions; Density functional theory; diazo compounds; Esters; Natural products; Phenols; Physical Sciences; Quinones; Science & Technology; transition-metal-free reaction; C(sp)-C(sp) bond; ROUTE; COMPLEXES; 1,2-DIAZONAPHTHOQUINONES; REACTIVITY; DIAZOCARBONYL COMPOUNDS; ALKENYLBORONIC ACIDS; C-H ARYLATION; ARYL; diazo compounds; DERIVATIVES; boronic esters; cross-coupling reactions; transition-metal-free reaction; DIAZIDES
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.202006542

A transition‐metal‐free C(sp2)−C(sp2) bond formation reaction by the cross‐coupling of diazo quinones with catechol boronic esters was developed. With this protocol, a variety of biaryls and alkenyl phenols were obtained in good to high yields under mild conditions. The reaction tolerates various functionalities and is applicable to the derivatization of pharmaceuticals and natural products. The synthetic utility of the method was demonstrated by the short synthesis of multi‐substituted triphenylenes and three bioactive natural products, honokiol, moracin M, and stemofuran A. Mechanistic studies and density functional theory (DFT) calculations revealed that the reaction involves attack of the boronic ester by a singlet quinone carbene followed by a 1,2‐rearrangement through a stepwise mechanism. Without transition metal catalysts, diazo quinones undergo cross‐coupling with catechol boronic esters to give a variety of biaryls and alkenyl phenols in up to 96 % yield under mild conditions. The reaction is applicable to the synthesis of multi‐substituted triphenylenes and natural products honokiol, moracin M, and stemofuran A. DFT calculations revealed a stepwise mechanism involving attack of the boronic ester by a singlet quinone carbene.