Visible-light induced copper(i)-catalyzed oxidative cyclization of o-aminobenzamides with methanol and ethanol via HAT

Visible light-mediated synthesis of quinazolinones and benzothiadiazine-1,1-dioxides utilizing aliphatic alcohols

The activation and utilization of challenging aliphatic alcohols like methanol and ethanol is a very appealing approach to synthesize valuable organic molecules. Utilization of methanol and ethanol as a coupling partner has emerged as a valuable alternative to synthesize industrially relevant N-heterocycles because they can be easily procured from renewable sources unlike other activated coupling partners which are expensive and also unstable. Herein, a mild and metal-free photocatalytic protocol to synthesize quinazolinones and more challenging benzothiadiazine-1,1-dioxides, which is unprecedented at room temperature, is demonstrated. This methodology showcased broad substrate scope and provided important N-heterocycles more efficiently than the transition metal-based high temperature protocols. An unexplored reactivity with allyl alcohol is observed following the developed protocol. A series of control experiments were carried out to understand the mechanism.

Photogenerated chlorine radicals activate C(sp3)-H bonds of alkylbenzenes to access quinazolinones

An Fe-catalyzed visible-light induced condensation of alkylbenzenes with anthranilamides has been developed. Upon irradiation, the trivalent iron complex could generate chlorine radicals, which successfully abstracted the hydrogen of benzylic C-H bonds to form benzyl radicals. And these benzyl radicals were converted into oxygenated products under air conditions, which subsequently reacted with anthranilamides for the synthesis of quinazolinones.

Cu-Catalyzed Carbocyclization for General Synthesis of N-Containing Heterocyclics Enabled by BrCF2COOEt as a C1 Source

A practical and efficient copper-catalyzed carbocyclization of 2-functionalized anilines with ethyl bromodifluoroacetate has been developed. Ethyl bromodifluoroacetate is employed as the C1 source via quadruple cleavage in this transformation. This reaction can afford a variety of N-containing heterocyclics with satisfactory yields and excellent functional group compatibility.

Photo-Induced C1 Substitution Using Methanol as a C1 Source

The development of sustainable and efficient C1 substitution methods is of central interest for organic synthesis and pharmaceuticals production, the methylation motifs bound to a carbon, nitrogen, or oxygen atom widely exist in natural products and top-selling drugs. In the past decades, a number of methods involving green and inexpensive methanol have already been disclosed to replace industrial hazardous and waste-generating C1 source. Among the various efforts, photochemical strategy is considered as a "renewable" alternative that shows great potential to selectively activate methanol to achieve a series of C1 substitutions at mild conditions, typically C/N-methylation, methoxylation, hydroxymethylation, and formylation. Herein the recent advances in selective transformation of methanol to various C1 functional groups via well-designed photochemical systems involving different types of catalysts or not is systematically reviewed. Both the mechanism and corresponding photocatalytic system were discussed and classified on specific methanol activation models. Finally, the major challenges and perspectives are proposed.

Structural Regulation of Two Polyoxometalate-Based Metal-Organic Frameworks for the Heterogeneous Catalysis of Quinazolinones

Two dimeric {ε-Zn₄PMo₁₂}-based metal-organic frameworks (MOFs), [ε-PMo₈^VMo₄^VIO₃₄(OH)₆Zn₄][LO] (SDUT-21, LO = [5-((4'-carboxybenzyl)oxy)isophthalic acid]) and [TBA]₃[ε-PMo₈^VMo₄^VIO₃₇(OH)₃Zn₄][LN] (SDUT-22, TBA⁺ = tetrabutylammonium ion, LN = [5-((4-carboxybenzyl)imino)isophthalic acid]), combining the advantages of polyoxometalates (POMs) and MOFs, were synthesized by the one-pot assembly strategy. The dimeric {ε-Zn₄PMo₁₂} units act as nodes that are linked by the flexible ligands and extended into two- or three-dimensional frameworks. The cyclic voltammetry and proton conductivity measurements of SDUT-21 and SDUT-22 were performed and indicated the high electron and proton transfer abilities. These materials also e xhibited the catalytic performance for the synthesis of quinazolinones in the heterogeneous state, and the different binding capacities toward the substrates caused the catalytic activity of SDUT-21 to be higher than that of SDUT-22 under the same conditions. In addition, the used catalysts could be readily recovered for five successive cycles and maintained high catalytic efficiency.

Controlled Photochemical Synthesis of Substituted Isoquinoline-1,3,4(2H)-triones, 3-Hydroxyisoindolin-1-ones, and Phthalimides via Amidyl Radical Cyclization Cascade

We report a controlled radical cyclization cascade of isoquinoline-1,3,4(2H)-triones, 3-hydroxyisoindolin-1-ones, and phthalimides from o-alkynylated benzamides by metal-free photoredox catalyzed amidyl N-centered radical addition to the C-C triple bond using the proton-coupled electron transfer (PCET) process under mild reaction conditions. A time tunable synthesis of 3-hydroxyisoindolin-1-ones and phthalimides via β-carbonyl-C(sp³) bond cleavage was also achieved under visible light irradiation. A mechanistic rationale for the radical cyclization cascade is supported by various control and quenching experiments as well as EPR studies.

UV-Light-Induced Dehydrogenative N-Acylation of Amines with 2-Nitrobenzaldehydes To Give 2-Aminobenzamides

A simple, mild, green, and efficient method for the synthesis of 2-aminobenzamides is highly desirable. Herein, we report the development of an efficient, one-pot strategy starting from 2-aminobenzaldehydes and amines with acetic acid in ethyl acetate/acetone using irradiation with UV light for the synthesis of 2-aminobenzamides in high yields; 32 examples proceeded successfully by this photo-induced protocol in up to 92% yield. The reaction was also readily achieved on a gram scale. The utility of the 2-aminobenzamide building block in organic synthesis was shown by their use in the preparation of quinazolinone derivatives. The method was applied to amino acid derivatives as the amine component, which smoothly gave N-(2-aminobenzoyl)acetate derivatives at room temperature. Finally, a plausible mechanism is proposed.

Metal-free photoredox-catalyzed direct α-oxygenation of N,N-dibenzylanilines to imides under visible light

An efficient synthesis of imides using metal-free photoredox-catalyzed direct α-oxygenation of N,N′-disubstituted anilines in the presence of 9-mesityl-10-methylacridinium [Acr⁺-Mes]BF₄ as a photoredox catalyst and molecular oxygen as a green oxidant under visible light was developed. This photochemical approach offered operational simplicity, high atom economy with a low E-factor, and functional group tolerance under mild reaction conditions. Control and quenching experiments confirmed the occurrence of a radical pathway and superoxide radical anion α-oxygenation reactions, and also provided strong evidence for the reductive quenching of [Acr⁺-Mes]BF₄ based on a Stern–Volmer plot, which led to the proposed mechanism of this reaction.

A visible-light-mediated direct α-oxygenation of N,N-dibenzylanilines to imides in the presence of [Acr⁺-Mes]BF₄ as a metal-free photocatalyst and O₂ as a green oxidant.

Regioselective Synthesis of 2° Amides Using Visible-Light-Induced Photoredox-Catalyzed Nonaqueous Oxidative C-N Cleavage of N,N-Dibenzylanilines

A visible-light-driven photoredox-catalyzed nonaqueous oxidative C-N cleavage of N,N-dibenzylanilines to 2° amides is reported. Further, we have applied this protocol on 2-(dibenzylamino)benzamide to afford quinazolinones with (NH₄)₂S₂O₈ as an additive. Mechanistic studies imply that the reaction might undergo in situ generation of α-amino radical to imine by C-N bond cleavage followed by the addition of superoxide ion to form amides.

Visible-light-mediated copper photocatalysis for organic syntheses

Photoredox catalysis has been applied to renewable energy and green chemistry for many years. Ruthenium and iridium, which can be used as photoredox catalysts, are expensive and scarce in nature. Thus, the further development of catalysts based on these transition metals is discouraged. Alternative photocatalysts based on copper complexes are widely investigated, because they are abundant and less expensive. This review discusses the scope and application of photoinduced copper-based catalysis along with recent progress in this field. The special features and mechanisms of copper photocatalysis and highlights of the applications of the copper complexes to photocatalysis are reported. Copper-photocatalyzed reactions, including alkene and alkyne functionalization, organic halide functionalization, and alkyl C-H functionalization that have been reported over the past 5 years, are included.

Electrochemical synthesis of isobenzofuran-1-imines using oxidative halocyclization of o-alkynylbenzamides

Electrochemical oxidative 5-exo-dig-oxo-halocyclization of o-alkynylbenzamides was achieved using readily available NaX (X = Cl, Br and I) salts under mild reaction conditions. The use of a cheap and highly stable sodium halide as a halide ion source is impressive for the synthesis of a variety of halogenated isobenzofuran-1-imines. This electrochemical protocol shows regioselectivity and excellent conversion to isobenzofuran-1-imines in good yields without the use of stoichiometric amounts of oxidants and transition metal catalysts.

Electrophilically Activated Nitroalkanes in Synthesis of 3,4-Dihydroquinozalines

Nitroalkanes activated with polyphosphoric acid serve as efficient electrophiles in reactions with various nucleophilic amines. Strategically placed second functionality allows for the design of annulation reactions enabling preparation of various heterocycles. This strategy was employed to develop an innovative synthetic approach towards 3,4-dihydroquinazolines from readily available 2-(aminomethyl)anilines.

Photoinduced Enhanced Decomposition of TBHP: A Convenient and Greener Pathway for Aqueous Domino Synthesis of Quinazolinones and Quinoxalines

Catalyst-free photoinduced processes in aqueous medium represent significant advancement toward development of green and sustainable pathways in organic synthesis. tert-Butyl hydroperoxide (TBHP) is a widely used oxidant in organic reactions, where the decomposition of TBHP into its radicals by metal catalysts or other reagents is a key factor for efficient catalytic outcome. Herein, we report a simple and environmentally friendly visible light-promoted synthetic pathway for the synthesis of N-heterocyclic moieties, such as quinazolinones and quinoxalines, in the presence of TBHP as an oxidizing agent in aqueous medium that requires no catalysts/photocatalysts. The enhanced rate of decomposition to generate free radicals from TBHP upon visible light irradiation is the driving force for the domino reaction.