Visible-Light-Mediated (sp 3)Cα-H Functionalization of Ethers Enabled by Electron Donor-Acceptor Complex

N-Hydroxyphthalimide/TiO2 Catalyzed Addition of Ethers, Alkylarenes and Aldehydes to Azodicarboxylates under Visible Light

The addition of carbon-centered radicals to double bonds is one of the most atom-efficient approaches to the formation of new C-C or C-heteroatom bonds. Existing approaches for the generation of carbon-centered radicals often require elevated temperatures, UV radiation or expensive transition metal catalysts. In this work, a photocatalytic system based on a heterogeneous TiO2 catalyst and a redox organocatalyst N-hydroxyphthalimide is proposed for the generation of carbon-centered radicals from C(sp3)-H substrates or aldehydes at room temperature under visible light irradiation. The developed approach was successfully applied to the addition of ethers, alkylarenes and aldehydes to azodicarboxylates. Titanium oxide acts as a photocatalyst, producing phthalimide-N-oxyl radicals from N-hydroxyphthalimide, thereby enabling the organocatalytic process in solution. Phthalimide-N-oxyl radicals act as catalytically active species that cleave C-H bonds to form carbon-centered radicals.

Exploiting N-Centered Umpolung Reactivity of α-Iminomalonates for the Synthesis of N-Sulfenylimines and Sulfonamides

An efficient and interesting N-centered umpolung method has been disclosed to construct beneficial S-N bonds, furnishing N-sulfenylimines, which can readily be converted into the corresponding sulfonamide derivatives in a one-pot sequential operation. N-Sulfenylimines are potent intermediates in organic synthesis, whereas sulfonamides are of major molecular interest due to their rich biological activities and wide applicability in medicinal chemistry. Owing to the simple reaction conditions and setup, this protocol displays a broad and versatile substrate scope, resulting in excellent functional group tolerability toward the synthesis of both N-sulfenylimines and sulfonamides. A density functional theory (DFT) computed and experimentally supported convenient mechanism has been proposed for this unique method.

Visible-Light-Induced Hydrogen Atom Transfer En Route to Exocylic Alkenylation of Cyclic Ethers Enabled by Electron Donor-Acceptor Complex

An electron donor-acceptor (EDA)-triggered hydrogen atom transfer (HAT) process is developed for the efficient generation of an α-alkoxy radical from cyclic ethers to synthesize exocyclic alkenylated ethers with exclusive E-selectivity. A judiciously chosen donor-acceptor pair (DABCO and maleimide) serves as the desired HAT reagent under visible light irradiation without using any photocatalyst or peroxide. A wide variety of substrates were explored to demonstrate the diverse applicability and practical viability of this cross-dehydrogenative transformation. Detailed mechanistic studies revealed a radical reaction pathway under the oxidative environment.

Visible-Light-Induced Oxyalkylation of 1,2,4-Triazine-3,5(2H, 4H)-diones with Ethers via Oxidative Cross-Dehydrogenative Coupling

An efficient and convenient method to synthesize 6-oxyalkylated 1,2,4-triazine-3,5(2H, 4H)-diones has been developed via visible-light-induced cross-dehydrogenative coupling reaction between 1,2,4-triazine-3,5(2H, 4H)-diones and ethers with a wide range of functional group tolerance. The present transformation employs the cheap and low-toxic 2-tert-butylanthraquinone as a metal-free photocatalyst and air as a green oxidant at room temperature. Moreover, this reaction can also be driven by sunlight as a clean energy resource. The synthetic utility of this method is further demonstrated by gram-scale reaction and application in the preparation of key intermediates of bioactive molecules.