Red-Light-Promoted Radical Cascade Reaction to Access Tetralins and Dialins Enabled by Zinc(II)porphyrin, A Light-Flexible Catalyst

[5,15-Bis(pentafluorophenyl)-10,20-diphenylporphinato]zinc(II) (1), a metalloporphyrin derivative that was recently reported as an efficient photocatalyst driven by blue LEDs by our group, was found to catalyze a red-light-promoted (630 nm LEDs) radical cascade reaction of N-3-arylpropionyloxyphthalimides with radicophiles including electron-deficient alkenes and alkynes, providing access to a range of functionalized tetralin and dialin derivatives. The radical cascade reaction catalyzed by 1 took place via an oxidative quenching cycle in DMSO, where no sacrificial electron donor was required, uncovering a unique solvent effect capable of promoting the porphyrin catalysis.

Red-light-mediated Barton decarboxylation reaction and one-pot wavelength-selective transformations

In organic chemistry, selecting mild conditions for transformations and saving energy are increasingly important for achieving sustainable development goals. Herein, we describe a red-light-mediated Barton decarboxylation using readily available red-light-emitting diodes as the energy source and zinc tetraphenylporphyrin as the catalyst, avoiding explosive or hazardous reagents or external heating. Mechanistic studies suggest that the reaction probably proceeds via Dexter energy transfer between the activated catalyst and the Barton ester. Furthermore, a one-pot wavelength-selective reaction within the visible light range is developed in combination with a blue-light-mediated photoredox reaction, demonstrating the compatibility of two photochemical transformations based on mechanistic differences. This one-pot process expands the limits of the decarboxylative Giese reaction beyond polarity matching.

Applications of red light photoredox catalysis in organic synthesis

Photoredox catalysis has emerged as an efficient and versatile approach for developing novel synthetic methodologies. Particularly, red light photocatalysis has attracted more attention due to its intrinsic advantages of low energy, few health risks, few side reactions, and high penetration depth through various media. Impressive progress has been made in this field. In this review, we outline the applications of different photoredox catalysts in a wide range of red light-mediated reactions including direct red light photoredox catalysis, red light photoredox catalysis through upconversion, and dual red light photoredox catalysis. Due to the similarities between near-infrared (NIR) and red light, an overview of NIR-induced reactions is also presented. Lastly, current evidence showing the advantages of red light and NIR photoredox catalysis is also described.

Performances of Homogeneous and Heterogenized Methylene Blue on Silica Under Red Light in Batch and Continuous Flow Photochemical Reactors

Methylene blue was efficiently immobilized on silica micro- and nanoparticles by electrostatic interactions and the performances of the heterogenized photocatalysts were compared against the homogeneous conditions using the photooxidation of citronellol as a model reaction under red light, in a batch and a continuous flow photochemical reactor. In batch, the heterogeneous photocatalyst outperforms the homogeneous one, presumably due to kinetic and stability effects. The two catalytic systems are also compared in a flow reactor displaying improved mass transfer properties. We demonstrate that this results in a dramatic enhancement in photocatalyst stability, reactivity and productivity. This study highlights the importance of photocatalyst stability under homogeneous versus heterogenized conditions and in batch versus flow photochemistry.