Discovery of an Oxidative System for Radical Generation from Csp³–H Bonds: A Synthesis of Functionalized Oxindoles

Abstract

A facile and versatile method for generating radicals from Csp3–H bonds under metal-free and organic-peroxide-free conditions was developed. By combining safe persulfate and low-toxic quaternary ammonium salt, a wide variety of Csp3–H compounds including ethers, (hetero)­aromatic/aliphatic ketones, alkylbenzenes, alkylheterocycles, cycloalkanes, and haloalkanes were selectively activated to generate the corresponding C-centered radicals, which could be further captured by N-arylacrylamides to deliver the valuable functionalized oxindoles. Good functional group tolerance was demonstrated. The useful polycarbonyl compound and esters were also modified with the strategy. Moreover, the combination can also be applied to the practical coupling between simple haloalkanes and N-hydroxyphthalimide (NHPI).

Carboazidation of Terminal Alkenes with Trimethylsilyl Azide and Cyclic Ethers Catalyzed by Copper Powder under Oxidative Conditions

“…For example, the diastereoselectivity improved with increasing substituent sizes of 3aa (phenyl), 3da (4,4′-biphenyl), and 3ga (1-naphthyl) to 1.1:1, 2:1, and 7:1, respectively. A large number of reactions have been reported using simple cyclic ethers to give mixtures of the two diastereomers with respect to addition to styrene . However, to the best of our knowledge, the highest diastereoselectivity reported in those studies is 1.5:1, and there is no precedent for improving diastereoselectivity by the bulkiness of substituents in the remote control of radical reactions.…”

Potassium Persulfate as an Eco-Friendly Oxidant for Oxidative Transformations

“…Zhang and Chen jointly reported K 2 S 2 O 8 −/tetrabutylammonium hydrogen sulfate (TBAHS) promoted cascade oxidative aryl-alkylation of N-Aryl-alkylation of N-aryl acrylamides for functionalized oxindole synthesis (Figure 5) [21]. Under the heating condition, K 2 S 2 O 8 interacted with TBAHS to produce bis(tetrabutylammonium) ) to obtain the desired product.…”

Divergent Radical Cyclization and Hydroaminoalkylation of N-Arylacrylamides Using Photoredox Catalysis

“…In recent years, N -arylacrylamides have received widespread interest as radical receptors and have been developed with a variety of radical precursors for the construction of the 2-hydroxyindole backbone (Scheme a) . Within this field, researchers have explored various strategies to trigger α-C–H bonding to generate alkyl radicals (Scheme b), and they use N -arylacrylamides to capture radicals to construct 2-hydroxyindole backbones with a quaternary carbon center . However, due to the high bond dissociation energy (BDE) of α-C–H, only a few works have been reported.…”