Photocatalytic Oxidative Dearomatization of Orcinaldehyde Derivatives

Abstract

For decades oxidative dearomatization has been employed as a key step in the synthesis of complex molecules. Challenges in controlling the chemo-and site-selectivity of this transformation have sparked the development of a variety of specialized oxidants; however, these result in stoichiometric amounts of organic byproducts. Herein, we describe a photocatalytic method for oxidative dearomatization using molecular oxygen as the stoichiometric oxidant. This provides environmentally benign entry to highly substituted o-quinols, reactive intermediates which can be elaborated to a number of natural product families.

Photochemical and Electrochemical Applications of Proton-Coupled Electron Transfer in Organic Synthesis

“…Narayan and Baker Dockrey recently presented an elegant, bioinspired solution to the oxidative de-aromatization of orcinaldehyde derivatives, developing a method with air as the terminal oxidant, a natural flavin photocatalyst FMN , and water as solvent ( Scheme 201 ). 549 This method avoids the use of synthetic noble metal photocatalysts and the generation of stoichiometric quantities of waste products, which occurs when traditional chemical oxidants are employed for phenol de-aromatization (Pb(OAc) 4 and hypervalent iodine reagents, for example). 550 The optimized conditions here consisted of blue-light irradiation of orcinaldehyde substrates in the presence of flavin mononucleotide (FMN) photocatalyst in tris pH = 8 aqueous buffer solution under an O 2 atmosphere.…”

“…SV fluorescence emission studies indicate that the resulting phenoxide quenches the photocatalyst approximately 200 times faster than the tris buffer ( K SV phenoxide = 206/M, compared to K SV tris = 1.13/M, under air). 549 Therefore, the photoexcited-state FMN most likely undergoes direct ET with the phenoxide to deliver the phenoxyl radical and FMN SQ semiquinone radical anion. The phenoxy radical reacts with triplet oxygen to yield a peroxy radical, which is reduced to the peroxide anion by the SQ form of the photocatalyst.…”

Protonation-Enhanced Reactivity of Triplet State in Dearomative Photocycloaddition of Quinolines to Olefins

“…Dearomatization of arenes is challenging because of the high chemical stability inherent due to aromaticity. Despite this, chemists have developed various dearomative transformations of arenes, which are currently indispensable tools for synthesizing complex molecules. − Photochemical methods are a common approach to induce the loss of aromaticity. − In particular, visible-light photocatalysis has emerged as an efficient and environmentally friendly tool for utilizing energy transfer − and electron transfer, − enabling sustainable reactions, including various dearomative reactions. − …”

Heterologous Expression of Secondary Metabolite Genes in Trichoderma reesei for Waste Valorization

“…The following are available online at https://www.mdpi.com/article/10 .3390/jof8040355/s1: all experimental details including growth media, buffers, enzyme, and antibiotic solutions; bacterial and fungal strains; vectors and oligonucleotides; tabulated NMR data; NMR spectra; and HRMS data. References [25,[28][29][30]32,33,45,[52][53][54][55][56][57][58][59][60][61][62] are cited in Supplementary Materials.…”