Photocatalytic Oxygenation of Heterostilbenes—Batch versus Microflow Reactor

Abstract

On the basis of earlier results with furan and thiophene derivatives of benzobicyclo[3.2.1]octadiene, photocatalytic oxygenation of novel furo- and thieno heterostilbenes with water-soluble manganese(III) porphyrins offered suitable possibilities to study their reactivities and reaction pathways depending on the heteroatom and the catalyst charge. The experiments were carried out in two reactors types (batch and microflow) to investigate the geometric effects. NMR spectroscopy, GC, and UPLC/MS analyses were applied for identification and quantification of the products. As our results indicated, the 2-thienyl and the common p-tolyl groups in the starting compounds remained intact due to their stronger aromaticity. Hence, the thieno derivative underwent oxygenation only at the open-chain part of the molecule, and the rates of its reactions were much lower than those of the furyl analogue. The less stable furan ring was easily oxygenated, its products with highest ratios were 2-furanon derivatives. Epoxide formation occurred at the open-chain parts of both substrates preferably by the anionic catalyst. Nevertheless, the conversion rates of the substrates were higher with the cationic porphyrin, according to electrophilic attacks by photogenerated Mn(V)=O species. Additionally, the reactions were significantly faster in microflow reactors due to the more favorable circumstances of mass transfer, diffusion, and light penetration.

Technological Innovations in Photochemistry for Organic Synthesis: Flow Chemistry, High-Throughput Experimentation, Scale-up, and Photoelectrochemistry

“…Horváth, Škoric, and co-workers reported the photocatalytic oxidation of heterostilbenes . Manganese­(III) porphyrins worked as the photocatalyst.…”

“…Horvath, S ̌koric, and co-workers reported the photocatalytic oxidation of heterostilbenes. 756 Manganese(III) porphyrins worked as the photocatalyst. Differently from metal-free porphyrins, these catalysts perform an electron transfer after light irradiation, affording Mn(IV) and Mn(V) complexes which are then involved in follow-up reactions.…”

Phosphonate-substituted porphyrins as efficient, cost-effective and reusable photocatalysts

“…These catalysts can be easily separated from the target products but their reuse was impossible probably due to their low photostability. [119][120][121] To knowledge, we report here the first example of an oxidation reaction in which water-soluble porphyrins can be recycled and reused.…”

“…It is noteworthy that the photocatalytic properties of watersoluble Mn(III) complexes for oxygenation of unsaturated compounds were thoroughly investigated. [119][120][121] In the case of sulfonate-substituted porphyrin derivatives, it was shown that free-base porphyrins can also be used as PCs. These catalysts can be easily separated from the target products but their reuse was impossible probably due to their low photostability.…”

Effects of Temperature, Axial Ligand, and Photoexcitation on the Structure and Spin-State of Nickel(II) Complexes with Water-Soluble 5,10,15,20-Tetrakis(1-methylpyridinium-4-yl)porphyrin

“…Water-soluble metalloporphyrins, due their special spectral, coordination, and photoredox features, offer numerous possibilities of application in various photochemical procedures, e.g., for visible light-driven photocatalysis [ 1 , 2 , 3 , 4 , 5 , 6 ]. These peculiar coordination and electronic properties are due in large part to the structure of the porphyrin ligand.…”