EDA mediated S-N bond coupling of nitroarenes and sodium sulfinate salts

Harnessing nitroarenes: photo-driven synergistic construction of phosphinic amides via hydrogen transfer and oxygen migration

A photo-mediated cascade rearrangement of nitroarenes in an electron donor-acceptor (EDA) complex generates phosphinic amides without metal or oxidants. Utilizing oxygen atoms from nitro groups, the reaction facilitates P(III) to P(V) conversion. The method shows broad substrate scope and compatibility with late-stage functionalization, offering potential for pharmaceutical synthesis.

Light-Induced Transformations of Donor-Donor Diazo Compounds Derived from N-Sulfonylhydrazones

The donor-donor carbene chemistry field is underdeveloped and often relies on harsh reaction conditions, utilizing either thermal or oxidative process with or without transition-metal catalysts. In this review, we discussed the synthesis and transformation of donor-donor diazo compounds from N-sulfonylhydrazones in the presence of light and base. The N-sulfonylhydrazones are easily accessible from the corresponding carbonyl compounds and sulfonyl hydrazides through condensation. The in situ generated N-sulfonyl anion in the presence of base would undergo the N-S bond cleavage with the aid of light to generate the donor-donor diazo compounds. The donor-donor diazo compounds showed various reactivity in the presence of light for the C-C and C-X bond formation, cyclopropanation reactions, and synthesis of nitrogen, oxygen-containing heterocyclic compounds, which all are discussed under metal-free conditions.

Anaerobic 1,2-/1,3-Hydroxytrifluoromethylation of Unactivated Alkenes Enabled by Photoexcited Nitroarenes

An anaerobic 1,2-/1,3-hydroxytrifluoromethylation of unactivated alkenes is described. This reaction proceeds in mild and environmentally friendly conditions without photocatalyst and metal catalyst, allowing access to a wide range of β- and γ-trifluoromethyl alcohols. Preliminary mechanistic investigations indicate that the accomplishment of this protocol relies on the dual functionality of the photoexcited triplet nitroarenes, which serve as the oxygen atom source and enable the single-electron transfer (SET) process with CF3SO2Na.

A General Photoactive H-Bonding EDA Complex Model Drives the Selective Hydrothiolation and Hydroxysulfenylation of Carbonyl Activated Alkenes

Excitation of photoactive electron donor-acceptor (EDA) complexes to generate radical is a promising approach in radical chemistry. In this study, we introduce a new model of H-bonding EDA complexes for the selective hydrothiolation and hydroxysulfenylation of carbonyl-activated alkenes with diverse thiols under visible light conditions. The reliability of this H-bonding EDA complex model has been confirmed by meticulous experimental and theoretical calculations. Mechanistic investigations have revealed the significant influence of the solvent in determining whether the excitation of photoactive H-bonding EDA complex leads to charge transfer (CT) or energy-charge transfer (En-CT), thereby controlling Markovnikov and anti-Markovnikov selectivity. Notably, the Quantum Theory of Atoms in Molecules (QTAIM) analysis clearly shows that the excited state of the C=O-H-S EDA complex involves closed-shell partially covalent interactions.

EDA Complex-Promoted Cascade Cyclization of Alkynes Enabling the Rapid Assembly of 3-Sulfonylindoles and Vinyl Sulfone Oxindoles

Herein, we disclose a photoinduced radical cascade cyclization of alkynes with sulfinates via a novel EDA complex for the synthesis of various 3-sulfonylindoles and vinyl sulfone oxindoles, which are crucial motifs in medicinal and biological chemistry. The reaction proceeds under mild, photocatalyst- and transition-metal-free conditions, featuring operational simplicity, broad substrate scope, and easy scalability. Mechanistic studies reveal that the reaction is initiated with a photoinduced intermolecular charge transfer from sulfinates to N-sulfonamides, generating a sulfonyl radical followed by an N-centered radical, thus enabling the cascade cyclization process.

Red-light-mediated copper-catalyzed photoredox catalysis promotes regioselectivity switch in the difunctionalization of alkenes

Controlling regioselectivity during difunctionalization of alkenes remains a significant challenge, particularly when the installation of both functional groups involves radical processes. In this aspect, methodologies to install trifluoromethane (-CF3) via difunctionalization have been explored, due to the importance of this moiety in the pharmaceutical sectors; however, these existing reports are limited, most of which affording only the corresponding β-trifluoromethylated products. The main reason for this limitation arises from the fact that -CF3 group served as an initiator in those reactions and predominantly preferred to be installed at the terminal (β) position of an alkene. On the contrary, functionalization of the -CF3 group at the internal (α) position of alkenes would provide valuable products, but a meticulous approach is necessary to win this regioselectivity switch. Intrigued by this challenge, we here develop an efficient and regioselective strategy where the -CF3 group is installed at the α-position of an alkene. Molecular complexity is achieved via the simultaneous insertion of a sulfonyl fragment (-SO2R) at the β-position. A precisely regulated sequence of radical generation using red light-mediated photocatalysis facilitates this regioselective switch from the terminal (β) position to the internal (α) position. Furthermore, this approach demonstrates broad substrate scope and industrial potential for the synthesis of pharmaceuticals under mild reaction conditions.

Visible light-induced metal-free cascade denitrogenative borylation and iodination of nitroarenes

An efficient method was developed for the one-pot construction of C-B and C-I via visible light-induced transformation of nitroarenes. This protocol relies on the photochemical properties of nitroarenes under visible light, followed by reduction with B2pin2 and diazotization with tBuONO. An array of arylboronates and iodobenzenes were constructed smoothly after excitation with purple LEDs at room temperature. In addition, the synthetic utility of this method was further demonstrated in the late-stage modification of a drug molecule. The advantages of this strategy include metal-free system, mild reaction conditions and acceptable substrate scope.

Photo-induced versatile aliphatic C-H functionalization via electron donor-acceptor complex

The ability to selectively introduce diverse functionality onto hydrocarbons is of substantial value in the synthesis of both small molecules and pharmaceuticals. In this endeavour, as a photocatalyst- and metal-free process, the electron donor-acceptor (EDA) strategy has not been well explored. Here we report an approach to aliphatic carbon-hydrogen bond diversification through an EDA complex constituted by HCl and SIV=O groups. As an efficient hydrogen atom transfer (HAT) reagent, chlorine radical can be produced via a proton-coupled electron transfer process in this system. Based on this unusual path, a photo-promoted versatile aliphatic C-H functionalization is developed without photo- and metal-catalysts, including thiolation, arylation, alkynylation, and allylation. This conversion has concise and ambient reaction conditions, good functional group tolerance, and substrate diversity, and provides an alternative solution for the high value-added utilization of bulk light alkanes.

Nitro-sulfinate Reductive Coupling to Access (Hetero)aryl Sulfonamides

A method to assemble (hetero)aryl sulfonamides via the reductive coupling of aryl sulfinates and nitroarenes is reported. Various reducing conditions with sodium bisulfite and with or without tin(II) chloride in DMSO were developed using an ultrasound bath to improve reaction homogeneity and mixing. A range of (hetero)aryl sulfonamides bearing a selection of functional groups were prepared, and the mechanism of the transformation was investigated. These investigations have led us to propose the formation of nitrosoarene intermediates, which were established via an independent molecular coupling strategy.

A General Platform for Visible Light Sulfonylation Reactions Enabled by Catalytic Triarylamine EDA Complexes

Catalytic electron donor-acceptor (EDA) complexes have recently emerged as a powerful and sustainable alternative to iridium- and ruthenium-based photoredox synthetic methods. Yet, these complexes remain underexplored and reliant on the use of meticulously designed acceptors that require previous installation. Herein, we report a novel EDA complex employing tris(4-methoxyphenyl) amine as a catalytic donor for the sulfonylation of alkenes using inexpensive and readily available sulfonyl chlorides. Applying this operationally simple, visible-light-mediated general platform, we report both the redox-neutral and net-reductive functionalization of more than 60 substrates, encompassing vinylic or allylic sulfonylation, hydrosulfonylation, and sulfamoylation of activated and unactivated alkenes and alkynes.

Visible-light-induced [3+2] cycloadditions of donor/donor diazo intermediates with alkenes to achieve (spiro)-pyrazolines and pyrazoles

To date, [3 + 2] cycloadditions of diazo esters with alkynes or alkenes have been a robust tool to generate pyrazoles and pyrazolines. However, methods capable of generating donor/donor diazo species from readily available N-tosylhydrazones to furnish [3 + 2] cycloadditions, remain elusive. Herein, we describe the first visible-light-induced [3 + 2] cycloadditions of donor/donor diazo precursors with alkenes to afford pyrazoles and novel (spiro)pyrazolines bearing a quaternary center. This protocol shows a tolerable substrate scope covering versatile carbonyl compounds and alkenes. Late-stage functionalization of bioactive molecules, one-pot approach, and gram-scale synthesis have also been introduced successfully to prove the practicability. At last, mechanistic experiments and DFT studies suggested the formation of non-covalent interactions enabling the activation of N-tosylhydrazones and the formation of the donor/donor diazo intermediates.

Metal- and Photocatalyst-Free, Visible-Light-Initiated C3 α-Aminomethylation of Quinoxalin-2(1H)-ones via Electron Donor-Acceptor Complexes

We report a metal- and photocatalyst-free C3 α-aminomethylation of quinoxalin-2(1H)-ones with N-alkyl-N-methylanilines. The reaction proceeds through the formation of a photoactivated electron donor-acceptor complex between quinoxalin-2(1H)-ones and N-alkyl-N-methylanilines. The present method provides a mild and environmentally friendly protocol that exhibits good atom economy and excellent functional group tolerance to obtain a library of biologically significant C3 α-aminomethylated quinoxalin-2(1H)-ones in good yields.