One-Step Transformation of Aryl Diazonium Salts into Aryl Indium(III) Reagents

A method for the conversion of diazonium salts into intrinsically nucleophilic aryl indium reagents is described. The reaction is performed using indium(I) bromide with the C-In bond being formed by the interaction of aryl radicals with the indium salt. The obtained aryl indium(III) reagents work well in the Liebeskind-Srogl cross-coupling with thioesters, affording a wide variety of aryl ketones. This two-step transformation is a general method for the acylation of diazonium salts.

Exploring the synthetic potential of epoxide ring opening reactions toward the synthesis of alkaloids and terpenoids: a review

Epoxides are oxygen containing heterocycles which are significantly employed as crucial intermediates in various organic transformations. They are considered highly reactive three-membered heterocycles due to ring strain and they undergo epoxide ring opening reactions with diverse range of nucleophiles. Epoxide ring-opening reactions have gained prominence as flexible and effective means to obtain various functionalized molecules. These reactions have garnered substantial attention in organic synthesis, driven by the need to comprehend the synthesis of biologically and structurally important organic compounds. They have also found applications in the synthesis of complex natural products. In this review article, we have summarized the implementation of epoxide ring opening reactions in the synthesis of alkaloids and terpenoids based natural products reported within the last decade (2014-2023).

A radical 1,4-aryl migration enables nickel-catalysed remote cross-electrophile coupling of β-bromo amino acid esters with vinyl triflates

A radical 1,4-aryl migration enabling a cross-electrophile coupling reaction toward remote transalkylation of N-benzyl alanine has been developed. In this strategy, with the occurrence of a radical-mediated Turce-Smiles rearrangement, key α-aminoalkyl radicals are generated. The as-formed α-aminoalkyl radical serves as a robust coupling partner for cross-electrophilic coupling with vinyl triflates, affording a series of olefin-tethered amino acid motifs.

Development and Applications of Water-Compatible Reactions: A Journey to Be Continued

ConspectusThe pursuit of novel and eco-friendly methods in organic synthesis is gaining prominence, with a strong emphasis on green transformations using renewable and sustainable resources. Among these environmentally conscious approaches, water-compatible reactions stand out for their many advantages. Water, as a solvent, offers unmatched abundance, cost-efficiency, and environmental compatibility compared to organic solvents. Its use eliminates the need for complex protection and deprotection steps for reactive functional groups in multistep synthesis and enables the use of water-soluble substrates like proteins and carbohydrates. Water-compatible reactions also provide opportunities to combine with enzymes, resulting in chemoenzymatic transformations that can increase efficiency. Additionally, these reactions facilitate site-specific modification and the bioconjugation of biomolecules, leading to bioconjugate therapeutics.Over nearly three decades, our research group has been dedicated to developing innovative water-compatible methodologies and concepts. This Account provides a comprehensive overview of our contributions since 1994. Our central strategy revolves around integrating green chemistry principles into our methods, focusing on (i) developing reactions that can operate under mild conditions, including room temperature, atmospheric pressure, and physiological pH; (ii) designing atom-economical reactions that minimize waste production; (iii) replacing toxic and flammable organic solvents with eco-friendly alternatives like water and ethanol; and (iv) reducing reliance on metals or halogenated compounds in specific reactions.In this Account, we detail our achievements in developing efficient methodologies in aqueous media, highlighting their scope, limitations, asymmetric control, and applications for synthesizing complex molecules and functionalizing peptides and proteins. Mechanistic investigations underlying these developments are also discussed when applicable. Furthermore, we offer insights into the reasoning behind our work and address future opportunities and challenges in this area of research. We hope that this Account will inspire continued interest and foster new breakthroughs. By exploring innovative and broadly applicable strategies that expand the water-compatible synthetic toolbox, we aim to pave the way for the truly green and sustainable synthesis of complex molecules and pharmaceuticals.

Transition-Metal-Catalyzed Directed C-H Functionalization in/on Water

Directing group assisted C-H bond functionalization using transition-metal-catalysis has emerged as a reliable synthetic tool for the construction of regioselective carbon-carbon/heteroatom bonds. Off late, "in/on water directed transition-metal-catalysis", though still underdeveloped, has appeared as one of the prominent themes in sustainable organic chemistry. This article covers the advancements, mechanistic insights and application of the sustainable directed C-H bond functionalization of (hetero)arenes in/on water in the presence of transition-metal-catalysis.

Advances in the Chemistry of 2,4,6-Tri(thiophen-2-yl)-1,3,5-triazine

Heterocyclic systems are now considered to be an integral part of material chemistry. Thiophene, selenophene, furan, pyrrole, carbazole, triazine and others are some such examples worth mentioning. 2,4,6-Tri(thiophen-2-yl)-1,3,5-triazine is a C3h -symmetric system with thiophene as the donor unit and s-triazine as the acceptor unit. This review gives an insight into the advances made in the thienyl-triazine chemistry over the past two to three decades. The synthetic pathways for arriving at this system and all its important derivatives are provided. The major focus is on the materials synthesized using the thienyl-triazine system, including star molecules, linear and hyperbranched polymers, porous materials and their diverse applications. This review will play a catalytic role for new dimensions to be explored in thienyl-triazine chemistry.

Expedient Ni-catalyzed C-H/C-H cross-dehydrogenative coupling of aryl amides with azoles

A nickel-catalyzed C-H heteroarylation of arenes has been described using a removable oxazoline-aniline derived directing group. Utilization of inexpensive nickel(II)-catalyst, substrate scope, functional group diversity and late-stage functionalization of xanthine-derived...

Multiple-fold C–F bond functionalization for the synthesis of (hetero)cyclic compounds: fluorine as a detachable chemical handle

We highlighted the recent advances in the field of multiple-fold C–F bond functionalization for the synthesis of (hetero)cyclic compounds.

Heterogeneous copper-catalyzed synthesis of diaryl sulfones

A carbon-supported copper nanoparticle (Cu-NP) with high catalytic activity for the synthesis of diaryl sulfones is reported. For the first time, this Cu-NP is proved to be able to effectively promote the reaction of arylboronic acids and arylsulfonyl hydrazides to generate diaryl sulfones at room temperature. The reaction shows excellent substrate universality, and substrates with different substituents can undergo the reaction smoothly, leading to the desired products in good yields. The Cu-NP is found to be made of low valence Cu based on XRD. Hence, the reaction catalyzed by the Cu-NP is believed to involve a Cu-mediated organometallic cycle.

Merging Iridium-Catalyzed C-H Borylations with Palladium-Catalyzed Cross-Couplings Using Triorganoindium Reagents

A versatile and efficient method to prepare borylated arenes furnished with alkyl, alkenyl, alkynyl, aryl, and heteroaryl functional groups is developed by merging Ir-catalyzed C-H borylations (CHB) with a chemoselective palladium-catalyzed cross-coupling of triorganoindium reagents (Sarandeses-Sestelo coupling) with aryl halides bearing a boronic ester substituent. Using triorganoindium cross-coupling reactions to introduce unsaturated moieties enables the synthesis of borylated arenes that would be difficult to access through the direct application of the CHB methodology. The sequential double catalyzed procedure can be also performed in one vessel.

Pd-catalyzed bidentate auxiliary assisted remote C(sp3)-H functionalization

Pd-catalyzed C-H functionalisation affords effective synthetic tools to construct C-C and C-X bonds. Despite the challenges, the distal functionalization of C(sp³)-H bonds has witnessed significant developments and the use of bidentate auxiliaries has garnished this area by providing an opportunity to control reactivity as well as selectivity beyond proximal sites. This article covers the recent developments on the Pd-catalyzed bidentate auxiliary-assisted distal C(sp³)-H functionalization and is categorized based on the nature of functionalizations.

Recent Advances in the Pd-Catalyzed Coupling of Arylhydrazines and Ammonium Salts via C-N Bond Cleavage

Both arylhydrazines and quaternary ammonium salts are readily accessible or commercially available chemicals that show versatile reactivity in Pd-catalyzed coupling reactions via C-N bond cleavage. A tremendous array of coupling reactions involving reaction partners such as organoborons, aryl silanes, alkenes, alkynes, arylation or alkylation reagents in C-H functionalization and carbonylation reactions are summarized, in which arylhydrazines or quaternary ammonium salts function as aryl or alkyl donors. This account mainly focuses on recent advances in Pd-catalyzed coupling reactions with arylhydrazines or quaternary ammonium salts via C-N bond cleavage, including mechanistic elucidations.

Indium(III)-Catalyzed Stereoselective Synthesis of Tricyclic Frameworks by Cascade Cycloisomerization Reactions of Aryl 1,5-Enynes

The indium(III)-catalyzed cascade cycloisomerization reaction of 1,5-enynes with pendant aryl nucleophiles is reported. The reaction proceeds in cascade under mild reaction conditions, using InI₃ (5 mol %) as a catalyst with a range of 1,5-enynes furnished with aryl groups (phenyl and phenol) at alkene (E and Z isomers) and with terminal and internal alkynes. Using 1-bromo-1,5-enynes, a one-pot sequential indium-catalyzed cycloisomerization and palladium-catalyzed cross-coupling with triorganoindium reagents were developed. The double cyclization is stereospecific and operates via a biomimetic cascade cation-olefin through 1,5-enyne cyclization (6-endo-dig) and subsequent C-C hydroarylation or C-O phenoxycyclization. Density functional theory (DFT) computational studies on 1,5-enynyl aryl ethers support a two-step mechanism where the first stereoselective 1,5-enyne cyclization produces a nonclassical carbocation intermediate that evolves to the tricyclic reaction product through a S_EAr mechanism. Using this approach, a variety of tricyclic heterocycles such as benzo[b]chromenes, phenanthridines, xanthenes, and spiroheterocyclic compounds are efficiently synthesized with high atom economy.

Transition-Metal-Catalyzed Directing Group Assisted (Hetero)aryl C-H Functionalization: Construction of C-C/C-Heteroatom Bonds

Transition-metal-catalyzed C-H functionalization is one of the fascinating scientific fronts in organic synthesis for the formation of conjugated arenes and has emerged as a benchmark to revolutionize the synthetic enterprise since past decades. In this realm, chelation-guided functionalization of C-H bonds using an exogenous directing group has received considerable attention recently for the expedient regioselective construction of C-C and C-heteroatom bonds as an efficient and sustainable alternative. This article outlines our contribution towards a wide variety of transformations that have been achieved by the directed C-H functionalization through the fine tuning of catalytic systems.

Solvent Effects on Heterogeneous Rate Constants for Indium Mediated Allylations

Indium mediated allylation is a highly selective tool for synthetic chemists to create carbon-carbon bonds, but the first step, heterogeneous reaction of allyl halides at solid indium surfaces, is still poorly understood. For example, the nature of the solvent dramatically affects the rate of reaction, but solvent choice is often based on empirical experiments. Fundamental kinetic studies are the best way to study this effect, but the determination of heterogeneous rate constants is challenging. In an effort to better understand solvent effects, we use optical microscopy to determine heterogeneous rate constants for IMA in aqueous acetonitrile, methanol, ethanol, and 2-propanol. We fit the reaction rate data over a range of mass transport rates using only two adjustable parameters, the heterogeneous rate constant and the mass transport rate. The results emphasize the critical importance of water in determining the rate of reaction. Surprisingly, the polarity of the organic solvent in the mix does not have a major effect on the rate. It is hypothesized that the oxygen atom in water and alcohols is an especially effective Lewis base to stabilize the transition state and the organoindium intermediates, similar to the importance of the oxygen in ethers for the formation of Grignard reagents. This study again demonstrates the power of microscopy for the study of heterogeneous reactions.

Access to 1-indolyltetrahydro-β-carbolines via metal-free cross-dehydrogenative coupling: the total synthesis of eudistomin U, isoeudistomin U and 19-bromoisoeudistomin U

A highly selective and captivating metal-free cross-dehydrogenative coupling for the cross-coupling of two reactive nucleophiles such as tetrahydro-β-carboline and indoles is developed. A series of 1-indolyltetrahydro-β-carboline derivatives were synthesized in excellent to moderate yields. Temperature, time and concentration control resulted in mono indolylation selectively. Moreover, the total synthesis of eudistomin U and isoeudistomin U and the first total synthesis of 19-bromoisoeudistomin U were accomplished.

Understanding the planar conformations in diarylsubstituted heteroarenes: structural and theoretical insights

We have synthesized and X-ray characterized a series of six diaryl-substituted heteroarenes in order to analyze unconventional intramolecular C_Ar–H⋯N/O in comparison to conventional H-bonds.

Synthesis of ortho-arylated and alkenylated benzamides by palladium-catalyzed denitrogenative cross-coupling reactions of 1,2,3-benzotriazin-4(3H)-ones with organoboronic acids

An efficient palladium-catalyzed denitrogenative cross-coupling reaction of 1,2,3-benzotriazin-4(3H)-ones with organoboronic acids is described. The reaction affords various ortho-aryl and alkenylated benzamides in good to high yields.

Stereoselective and Atom-Economic Alkenyl C-H Allylation/Alkenylation in Aqueous Media by Iridium Catalysis

A practical and atom-economic protocol for the stereoselective preparation of various 1,4- and 1,3-diene skeletons through iridium-catalyzed directed olefinic C-H allylation and alkenylation of NH-Ts acrylamides in water was developed. This reaction tolerated a wide scope of substrates under simple reaction conditions and enabled successful gram-scale preparation. Furthermore, an asymmetric variant of this reaction giving enantioenriched 1,4-dienes was achieved employing a chiral diene-iridium complex as the catalyst.

Deaminative carbonylative coupling of alkylamines with styrenes under transition-metal-free conditions

Transition-metal-free deaminative carbonylation through C–N bonds activation via Katritzky salts has been successful developed. Various α,β-unsaturated ketones were obtained in moderate to good yields with alkylamines and styrenes as the substrates.

A Co–Cu bimetallic magnetic nanocatalyst with synergistic and bifunctional performance for the base-free Suzuki, Sonogashira, and C–N cross-coupling reactions in water

A novel bimetallic catalytic system based on Cu/Co has been developed and used as an efficient, eco-friendly, and recyclable catalyst for base- and Pd-free Sonogashira, Suzuki and C–N cross-coupling reactions in mild reaction conditions.

Indium-mediated difunctionalization of iodoalkyl-tethered unactivated alkenes via an intramolecular cyclization and an ensuing palladium-catalyzed cross-coupling reaction with aryl halides

A cobalt-catalyzed, indium-mediated difunctionalization of iodoalkyl-tethered unactivated alkenes for accessing five-membered cyclic compounds via a cyclization/cross-coupling sequence was developed.

2,3-Dimethoxyindolines: a latent electrophile for SNAr reactions triggered by indium catalysts

An unprecedented utilization of 2,3-dimethoxyindolines (DiMeOINs) as a latent electrophile in regioselective In-catalyzed aromatic substitutions has been reported.

Palladium-Catalyzed Carbonylative Coupling of Aryl Iodides with Alkenylaluminum Reagents

A highly reactive catalytic system for the carbonylative coupling of aryl iodides with alkenylaluminum reagents has been developed. Various β-substituted γ,δ-unsaturated ketones were produced under mild conditions in good to excellent yields even under ppm level of palladium catalyst. Notably, this also represents the first example on carbonylative transformation of alkenylaluminum compounds. Additionally, by the addition of zinc salt, the selectivity of the product can be modified.