Functionalized Oxindole Construction via a Cyano Migration and Cyclization Relay Strategy

A visible-light-induced trifunctionalization of unactivated alkenes for building functionalized oxindoles through a radical cyano migration strategy is reported. This transformation employs a tandem alkene sulfonylation-initiated cyano migration/cyclization cascade process. This strategy features stable and easily accessible substrates, mild reaction conditions, metal-free catalysts, and the capability of late-stage functionalization.

Remote radical alkynylation of unactivated C(sp3)-H bonds of ethynesulfonamides

We report an efficient protocol for the construction of δ-alkynyl amides via 1,5-hydrogen atom transfer and alkynyl group transfer of ethynesulfonamides. The readily installed ethynesulfonamides serve as both an amidyl radical precursor and an alkyne source. This reaction features excellent site selectivity for tertiary, secondary, primary, and benzylic C(sp3)-H bonds.

Intramolecularly remote functional group migration reactions involving free radicals

The application of rearrangement reactions offers opportunities for the efficient construction of complex molecules that are challenging to obtain through conventional synthetic methods. However, the development of radical-mediated rearrangements has lagged far behind that of ionic-type rearrangements, due to the uncontrollability of radical species. Along with the recent renaissance in radical chemistry, radical-mediated functional group migration (FGM) reactions provide a versatile platform for the selective incorporation of functional groups across different molecular distances, enabling the construction of intricate molecular architectures. In the past few years, FGM reactions have showcased plentiful reaction modes, rendering precious control in terms of chemo- and regio-selectivities. This feature article summarizes our achievements in radical-mediated FGM reactions, wherein brief discussion of related works from other laboratories is also included. In this feature article, we aim to provide a comprehensive understanding of the progress in this emerging area.

Sulfonamide-directed site-selective functionalization of unactivated C(sp3)-H enabled by photocatalytic sequential electron/proton transfer

The generation of alkyl radical from C(sp3)-H substrates via hydrogen atom abstraction represents a desirable yet underexplored strategy in alkylation reaction since involving common concerns remain adequately unaddressed, such as the harsh reaction conditions, limited substrate scope, and the employment of noble metal- or photo-catalysts and stoichiometric oxidants. Here, we utilize the synergistic strategy of photoredox and hydrogen atom transfer (HAT) catalysis to accomplish a general and practical functionalization of unactived C(sp3)-H centers with broad reaction scope, high functional group compatibility, and operational simplicity. A combination of validation experiments and density functional theory reveals that the N-centered radicals, generated from free N - H bond in a stepwise electron/proton transfer event, are the key intermediates that enable an intramolecular 1,5-HAT or intermolecular HAT process for nucleophilic carbon-centered radicals formation to achieve heteroarylation, alkylation, amination, cyanation, azidation, trifluoromethylthiolation, halogenation and deuteration. The practical value of this protocol is further demonstrated by the gram-scale synthesis and the late-stage functionalization of natural products and drug derivatives.

Copper-Catalyzed Asymmetric Remote C(sp3)-H Alkylation of N-Fluorocarboxamides with Glycine Derivatives and Peptides

Saturated hydrocarbon bonds are ubiquitous in organic molecules; to date, the selective functionalization of C(sp3)-H bonds continues to pose a notorious difficulty, thereby garnering significant attention from the synthetic chemistry community. During the past several decades, a wide array of powerful new methodologies has been developed to enantioselectively modify C(sp3)-H bonds that is successfully applied in asymmetric formation of diverse bonds, including C-C, C-N, and C-O bonds; nevertheless, the asymmetric C(sp3)-H alkylation is elusive and, therefore, far less explored. In this work, we report a direct and robust strategy to construct highly valuable enantioenriched unnatural α-amino acid (α-AA) cognates and peptides by a copper-catalyzed enantioselective remote C(sp3)-H alkylation of N-fluorocarboxamides and readily accessible glycine esters under ambient conditions. The key to success lies in the optically active Cu catalyst generated through the coordination of glycine derivatives to enantiopure bisphosphine/Cu(I) species, which is beneficial to the single electronic reduction of N-fluorocarboxamides and the subsequent stereodetermining alkylation. More importantly, all types (primary, secondary, tertiary, and even α-oxy) of δ-C(sp3)-H bonds could be site- and stereospecifically activated by the kinetically favored 1,5-hydrogen atom transfer (1,5-HAT) step.

Intramolecular trapping of spiro radicals to produce unusual cyclization products from usual migration substrates

A conceptually new methodology to give unusual cyclization products from usual migration substrates was disclosed. The highly complex and structurally important and valuable spirocyclic compounds were produced through radical addition, intramolecular cyclization and ring opening instead of usual migration to the di-functionalization products of olefins. Furthermore, a plausible mechanism was proposed based on a series of mechanistic studies including radical trapping, radical clock, verification experiments of intermediates, isotope labeling and KIE experiments.

Radical Heteroarylation of Alkenes and Alkanes via Heteroaryl Migration

Heteroarenes are important units in organic chemistry and are ubiquitous in natural products, pharmaceuticals, and numerous artificial molecules. Despite great efforts devoted to accessing heteroarenes, the development of new methods to efficiently produce heteroarenes remains a long-term interest. Recently, the strategy of radical-mediated heteroaryl migration has supplied a robust toolkit for the synthesis of a diversity of heteroaryl-containing compounds. This Account summarizes our recent achievements in this field and provides insight into the incorporation of heteroarenes into organic skeletons.

Radical trifunctionalization of hexenenitrile via remote cyano migration

A novel radical-mediated trifunctionalization of hexenenitriles via the strategy of remote functional group migration is disclosed. A portfolio of functionalized hexenenitriles are employed as substrates. After difunctionalization of the unactivated alkenyl part via remote cyano migration, the in situ formed radical intermediate is captured by an azido radical, thus enabling the trifunctionalization. The reaction features mild conditions and broad functional group compatibility, leading to valuable products bearing multiple useful groups. This protocol further extends the scope of remote functional group migration.