Divergent Synthesis of Bisphenols and Diaryl Ethers by Metal Compatible Organocatalytic Aerobic Oxidation of Boronic Acids

Abstract

Activation of dioxygen by monooxygenase enzymes enables the oxidation of a rich variety of substrates mainly due to the compatibility of this process with redox active metals. The current study shows that similarly to monooxygenases, pyrrole‐proline 2,5‐diketopiperazine (DKP) organocatalyst, in the presence of Hantzsch ester and HFIP is compatible with copper(II) salts for the activation of dioxygen. These findings allow to selectively diverge the oxidation profile of boronic acids for the synthesis of phenols, bisphenols and diaryl ethers by DKP‐promoted aerobic oxidation and subsequent metal oxidative‐coupling or Chan‐Lam‐Evans type reaction of the formed phenols.

Anthraquinone-Catalyzed Photooxidation of Boronic Acids in a Bio-Based Solvent (2-Me-THF)

“…Recently, Zografos and coworkers reported an organocatalytic oxidation of boronic acids, utilizing a proline-based organocatalyst. 12…”

“…Recently, Zografos and coworkers reported an organocatalytic oxidation of boronic acids, utilizing a prolinebased organocatalyst. 12 Over the past decade, three independent seminal contributions by MacMillan, 13 Yoon, 14 and Stephenson 15 added another option in the researcher's arsenal. The field of photochemistry, which was forgotten for more than a century, offered new opportunities triggering the formation of challenging chemical transformations under milder reaction conditions.…”

UVA‐Light‐Promoted Catalyst‐Free Photochemical Aerobic Oxidation of Boronic Acids

“…Recently, Zografos and coworkers designed a proline-based catalyst to activate oxygen for the same transformation. [10] In most cases, major drawbacks, such as prolonged reaction times and/or excess of oxidant narrow down their application. Another major issue arises from the use of handmade metal-based catalysts [7] or organocatalysts, [10] whose preparation poses extra difficulties in the implementation of those protocols.…”

“…[10] In most cases, major drawbacks, such as prolonged reaction times and/or excess of oxidant narrow down their application. Another major issue arises from the use of handmade metal-based catalysts [7] or organocatalysts, [10] whose preparation poses extra difficulties in the implementation of those protocols. In 2008, MacMillan, [11] Yoon [12] and Stephenson [13] almost simultaneously turned the lights on a "forgotten" research field called photoredox catalysis.…”

“…A plethora of metal‐mediated [8] or organocatalytic [9] protocols have been developed, employing either oxygen or hydrogen peroxide as the oxidant of choice. Recently, Zografos and coworkers designed a proline‐based catalyst to activate oxygen for the same transformation [10] . In most cases, major drawbacks, such as prolonged reaction times and/or excess of oxidant narrow down their application.…”