Sulfonamide-Directed Chemo- and Site-Selective Oxidative Halogenation/Amination Using Halogenating Reagents Generated in Situ from Cyclic Diacyl Peroxides

Visible light-induced PPh3/MI-promoted δ-C(sp3)-H chlorination and cyclization with N-chloro-arylsulfonamides via EDA complexes

Triphenylphosphine, iodide and N-chloro-arylsulfonamides could generate amidyl radicals via EDA (Electron Donor-Acceptor) complexes under visible light irradiation, and this strategy enables the synthesis of valuable δ-chloro-arylsulfonamide and N-arylsulfonylpyrrolidine motifs in moderate yields. This blue LED-induced method utilizes more readily available reagents, providing advantages in terms of cost efficiency, broad substrate scope, and functional-group compatibility.

Remote C-H Amination and Alkylation of Camphor at C8 through Hydrogen-Atom Abstraction

Camphor continues to serve as a versatile chiral building block for chemical synthesis. We have developed a novel method to functionalize the camphor skeleton at C8 using an intramolecular hydrogen atom abstraction. The key advance involves the use of a camphor-derived aminonitrile, which is converted to the corresponding nitrogen-centered radical under photoredox conditions to effect the 1,5-hydrogen atom transfer at C8. The resulting carbon-centered radical at C8 was utilized in a C-H amination to access topologically complex proline derivatives. Furthermore, the total synthesis of several sesquiterpenoids was accomplished by engaging the radical generated at C8 in alkylation reactions.

Iodine-Mediated δ-Amination of sp3 C-H Bonds

We present a direct δ-amination reaction of sp3 C-H bonds, employing molecular iodine (I2) as the sole oxidant under transition-metal-free conditions. This remote C-H functionalization approach is operationally simple and provides facile, efficient access to pyrrolidines and related heterocyclic derivatives from readily accessible substrates.

Synthesis of C3-halo substituted bicyclo[1.1.1]pentylamines via halosulfoamidation of [1.1.1]propellane with sodium hypohalites and sulfonamides

Herein, we report a catalyst-free synthesis of C3-halo substituted bicyclo[1.1.1]pentylamines under mild conditions. The reaction involves the use of sodium hypohalites and sulfonamides to generate N-halosulfonamides in situ, which subsequently undergo radical addition with [1.1.1]propellane to yield the desired products with suitable functional group tolerance.

Intramolecular C-H Amination of N-Alkylsulfamides by tert-Butyl Hypoiodite or N-Iodosuccinimide

1,3-Diamines are an important class of compounds that are broadly found in natural products and are also widely used as building blocks in organic synthesis. Although the intramolecular C-H amination of N-alkylsulfamide derivatives is a reliable method for the construction of 1,3-diamine structures, the majority of these methods involve the use of a transition-metal catalyst. We herein report on a new transition-metal-free method using tert-butyl hypoiodite (t-BuOI) or N-iodosuccinimide (NIS), enabling secondary non-benzylic and tertiary C-H amination reactions to proceed. The cyclic sulfamide products can be easily transformed into 1,3-diamines. Mechanistic investigations revealed that amination reactions using t-BuOI or NIS each proceed via different pathways.

Photoredox-Mediated Mono- and Difluorination of Remote Unactivated Methylene C(sp3)-H Bonds of N-Alkyl Sulfonamides

A photoredox-mediated δ-C(sp³)-H fluorination of sulfonyl-protected primary alkylamines with Selectfluor is developed. The reaction can proceed in excellent monofluorination selectivity for amine substrates without α substituent. For α-substituted substrates, a slightly modified reaction conditions with two rounds of operation gives the δ,δ-difluorination products in good yield. Mechanistic studies suggest SET oxidation of sulfonamide group directly generates the key sulfonamide N radical intermediate, which triggers a 1,5-HAT process to form the δ alkyl radical.

Energy Read-out as a Probe of Kinetically Hidden Transition States

The initial energy in a reactive intermediate is derived from the transition state before the intermediate but can affect selectivity after the intermediate. In this way an observable selectivity can report on a prior, kinetically hidden mechanistic step. This new type of mechanistic probe is demonstrated here for the oxidation of 1-methylcyclobutanol by phthaloyl peroxide/Bu₄N⁺Br^-, and it supports a hypobromite chain mechanism in place of the previously proposed hydrogen atom transfer mechanism.

Oxidative α-acyloxylation of acetals with cyclic diacyl peroxides

Selective functionalization of the non-activated acetal α-position with formal retaining of the acetal fragment was realized using cyclic diacyl peroxides.

Site-Specific C(sp3 )-H Aminations of Imidates and Amidines Enabled by Covalently Tethered Distonic Radical Anions

The utilization of N-centered radicals to synthesize nitrogen-containing compounds has attracted considerable attention recently, due to their powerful reactivities and the concomitant construction of C-N bonds. However, the generation and control of N-centered radicals remain particularly challenging. We report a tethering strategy using SOMO-HOMO-converted distonic radical anions for the site-specific aminations of imidates and amidines with aid of the non-covalent interaction. This reaction features a remarkably broad substrate scope and also enables the late-stage functionalization of bioactive molecules. Furthermore, the reaction mechanism is thoroughly investigated through kinetic studies, Raman spectroscopy, electron paramagnetic resonance spectroscopy, and density functional theory calculations, revealing that the aminations likely involve direct homolytic cleavage of N-H bonds and subsequently controllable 1,5 or 1,6 hydrogen atom transfer.

Visible-light-promoted N-centered radical generation for remote heteroaryl migration

An efficient visible-light-mediated organocatalyzed N–H heteroarylation was accomplished via remote heteroaryl ipso-migration.

Photoredox-Mediated Remote C(sp3)-H Heteroarylation of N-Alkyl Sulfonamides

A Minisci-type δ-selective C(sp³)-H heteroarylation of sulfonyl-protected primary aliphatic amines with N-heteroarenes under photoredox-catalyzed conditions was developed. The reaction typically uses a slight excess of amine reactant. The use of benziodoxole acetate (BI-OAc) oxidant and hexafluoroisopropanol solvent is critical to achieve high yield. Besides methylene C-H bonds, heteroarylation reactions of δ methyl C-H bonds also worked under more forced conditions. The reactions show a broad scope for both amine and N-heteroarene substrates, offering a straightforward method for synthesis of complex δ-heteroarylalkylmines from simple precursors.

Enantioselective Synthesis of Nicotine via an Iodine-Mediated Hofmann-Löffler Reaction

An iodine-mediated Hofmann-Löffler reaction has been developed that enables the first enantioselective synthesis of nicotine based on this synthetic methodology. The effect of the free pyridine core on the involved electrophilic iodine reagents was explored in detail. The final synthesis proceeds under moderate reaction conditions that tolerate the free pyridine core. The same synthetic sequence is also applicable to a number of derivatives with higher substituted pyridine cores, including bipyridine derivatives.

Catalytic β C-H amination via an imidate radical relay

An iodine-catalyzed strategy for β C–H amination of alcohols is enabled by a chemo-, regio-, and stereo-selective H-atom transfer mechanism.

The first catalytic strategy to harness imidate radicals for C–H functionalization has been developed. This iodine-catalyzed approach enables β C–H amination of alcohols by an imidate-mediated radical relay. In contrast to our first-generation, (super)stoichiometric protocol, this catalytic method enables faster and more efficient reactivity. Furthermore, lower oxidant concentration affords broader functional group tolerance, including alkenes, alkynes, alcohols, carbonyls, and heteroarenes. Mechanistic experiments interrogating the electronic nature of the key 1,5 H-atom transfer event are included, as well as probes for chemo-, regio-, and stereo-selectivity.

A General Approach to Site-Specific, Intramolecular C-H Functionalization Using Dithiocarbamates

Intramolecular hydrogen atom transfer is an established approach for the site-specific functionalization of unactivated, aliphatic C-H bonds. Transformations using this strategy typically require unstable intermediates formed using strong oxidants and have mainly targeted C-H halogenations or intramolecular aminations. Herein, we report a site-specific C-H functionalization that significantly increases the synthetic scope and convergency of reactions proceeding via intramolecular hydrogen atom transfer. Stable, isolable N-dithiocarbamates are used as precursors to amidyl radicals formed via either light or radical initiation to efficiently deliver highly versatile alkyl dithiocarbamates across a wide range of complex structures.

Two catalytic protocols for Achmatowicz rearrangement using cyclic diacyl peroxides as oxidants

The development of two new catalytic protocols for Achmatowicz rearrangement using cyclic diacyl peroxides as terminal oxidants.