Highly Ligand-Controlled Regioselective Pd-Catalyzed Aminocarbonylation of Styrenes with Aminophenols

Modular and Diverse Synthesis of Acrylamides by Palladium-Catalyzed Hydroaminocarbonylation of Acetylene

The development of all kinds of covalent drugs had a major impact on the improvement of the human health system. Covalent binding to target proteins is achieved by so-called electrophilic warheads, which are incorporated in the respective drug molecule. In the last decade, specifically acrylamides emerged as attractive warheads in covalent drug design. Herein, a straightforward palladium-catalyzed hydroaminocarbonylation of acetylene has been developed, allowing a modular and diverse synthesis of bio-active acrylamides. This general protocol features high atom efficiency, wide functional group compatibility, high chemoselectivity and proceeds additive free under mild reaction conditions. The synthetic utility of this protocol is showcased in the synthesis of ibrutinib, osimertinib, and other bio-active compound derivatives.

Single-Pd-Site Catalyst Induced by Different Dimensional Nitrogen of N-Doping Carbon for Efficient Hydroaminocarbonylation of Alkynes

The unsaturated amides are traditionally synthesized by acylation of carboxylic acids or hydration of nitrile compounds but are rarely investigated by hydroaminocarbonylation of alkynes using heterogeneous single-metal-site catalysts (HSMSCs). Herein, single-Pd-site catalysts supported on N-doping carbon (NC) with different nitrogen dimensions inherited from corresponding metal-organic-framework precursors are successfully synthesized. 2D NC-supported single-Pd-site (Pd1/NC-2D) exhibited the best performance with near 100% selectivity and 76% yield of acrylamide for acetylene hydroaminocarbonylation with better stability, superior to those of Pd1/NC-3D, single-metal-site/nanoparticle coexisting catalyst, and nanoparticle catalyst. The coordination environment and molecular evolution of the single-Pd-site during the process of acetylene hydroaminocarbonylation on Pd1/NC-2D are detailly illuminated by various characterizations and density functional theoretical calculations (DFT). DFT also showed the energy barrier of rate-determining step on Pd1/NC-2D is lower than that of Pd1/NC-3D. Furthermore, Pd1/NC-2D catalyst illustrated the general applicability of the hydroaminocarbonylation for various alkynes.

Palladium-catalyzed ligand-regulated divergent synthesis of pyrrole[2,3-b]indoles and ureas from 2-ethynylanilines and isocyanides

Herein, a palladium-catalyzed and ligand-controlled protocol for the divergent synthesis of pyrrole[2,3-b]indole and urea derivatives has been described. Pyrrole[2,3-b]indoles ("cyclization on" products) via tandem cyclization of o-alkynylanilines with isocyanides in the absence of a ligand and ureas ("cyclization off" products) via oxidative amination of anilines with isocyanides in the presence of a ligand were obtained both in moderate to good yields with high selectivity. In this chemistry, cyclic and acyclic products were easily accessed with the same starting materials under the regulation of the ligand.

Regiodivergent Carbonylation of Alkenes: Selective Palladium-Catalyzed Synthesis of Linear and Branched Selenoesters

An unprecedented regiodivergent palladium-catalyzed carbonylation of aromatic alkenes has been developed. Utilizing commercially available Pd(CH3 CN)2 Cl2 in the presence of 1,1'-ferrocenediyl-bis(tert-butyl(pyridin-2-yl)phosphine) ligand L8 diverse selenoesters are obtained in a straightforward manner. Key to success for the control of the regioselectivity of the carbonylation step is the concentration of the acidic co-catalyst. This general protocol features wide functional group compatibility and good regioselectivity. Mechanistic studies suggest that the presence of stoichiometric amounts of acid changes the properties and coordination mode of the ligand leading to reversed regioselectivity.

Cobalt-catalyzed synthesis of amides from alkenes and amines promoted by light

Catalytic methods to couple alkene and amine feedstocks are valuable in synthetic chemistry. The direct carbonylative coupling of alkenes and amines holds promise as a perfectly atom-economical approach to amide synthesis, but general methods remain underdeveloped. Herein, we report an alkene hydroaminocarbonylation catalyzed by unmodified, inexpensive cobalt carbonyl under mild conditions and low pressure promoted by light. Silane addition after the reaction enables sequential cobalt-catalyzed amide reduction, constituting a formal alkene hydroaminomethylation. These methods exhibit exceptional scope across both alkene and amine components with high chemo- and regioselectivity and proceed efficiently even in the absence of solvent. The formation of a hydridocobalt through photodissociation of a carbonyl ligand is proposed to enable catalytic activity under mild conditions, which addresses a long-standing challenge in catalysis.

Recent advances in ligand-enabled palladium-catalyzed divergent synthesis

Developing efficient and straightforward strategies to rapidly construct structurally distinct and diverse organic molecules is one of the most fundamental tasks in organic synthesis, drug discovery and materials science. In recent years, divergent synthesis of organic functional molecules from the same starting materials has attracted significant attention and has been recognized as an efficient and powerful strategy. To achieve this objective, the proper adjustment of reaction conditions, such as catalysts, solvents, ligands, etc., is required. In this review, we summarized the recent efforts in chemo-, regio- and stereodivergent reactions involving acyclic and cyclic systems catalyzed by palladium complexes. Meanwhile, the reaction types, including carbonylative reactions, coupling reactions and cycloaddition reactions, as well as the probable mechanism have also been highlighted in detail.

Electrochemical selenium-catalyzed para-amination of N-aryloxyamides: access to polysubstituted aminophenols

Aminophenols are a class of important compounds with various pharmacological activities such as anticancer, anti-inflammatory, antimalarial, and antibacterial activities. Herein, we introduce a mild and efficient electrochemical selenium-catalyzed strategy to synthesize polysubstituted aminophenols. High atom efficiency and transition metal-free and oxidant-free conditions are the striking features of this protocol. By merging electrochemical and organoselenium-catalyzed processes, the intramolecular rearrangement of N-aryloxyamides produces para-amination products at room temperature in a simple undivided cell.

Regioselective and Enantioselective Copper-Catalyzed Hydroaminocarbonylation of Unactivated Alkenes and Alkynes

Given the prevalence of amide backbones in marketed pharmaceuticals and their ubiquity as critical binding units in natural peptides and proteins, it remains important to develop novel methods to construct amide bonds. We report here a general method for the anti-Markovnikov hydroaminocarbonylation of unactivated alkenes under mild conditions, using copper catalysis in combination with hydroxylamine electrophile reagents and poly(methylhydrosiloxane) (PMHS) as a cheap and environmentally friendly hydride source. The reaction tolerates a variety of functional groups and efficiently converts unactivated terminal alkenes, 1,1-disubstituted alkenes, and cyclic alkenes to the corresponding amides with exclusive anti-Markovnikov selectivity (and high enantioselectivities/diastereoselectivities). Additionally, with minimal modification of the reaction conditions, alkynes can also undergo tandem hydrogenation-hydroaminocarbonylation to alkyl amides.

Palladium-catalyzed regiodivergent hydrochlorocarbonylation of alkenes for formation of acid chlorides

Novel strategy for acid chlorides formation that do not use carboxylic acids is particularly attractive in chemical synthesis but remains challenging. Herein, we reported the development of a highly effective Pd-catalyzed hydrochlorocarbonylation of alkenes with CO for the formation of alkyl acid chlorides. Chlorosilane and AcOH were found as a mild HCl source for the reaction. The reaction shows broad substrate scope and produces both branched and linear alkyl acid chlorides in good to high yields upon different ligands and solvents. Cooperating with follow-up acylation reactions, the Pd-catalyzed hydrochlorocarbonylation offers a complementary platform for the synthesis of diverse carbonyl compounds from alkenes. Mechanistic investigations suggested that the reaction proceeded though a palladium hydride pathway, and CO prompted reductive elimination of the acyl-Pd-Cl intermediate.

In Silico-Guided Rational Drug Design and Synthesis of Novel 4-(Thiophen-2-yl)butanamides as Potent and Selective TRPV1 Agonists

We describe an in silico-guided rational drug design and the synthesis of the suggested ligands, aimed at improving the TRPV1-ligand binding properties and the potency of N-(4-hydroxy-3-methoxybenzyl)-4-(thiophen-2-yl) butanamide I, a previously identified TRPV1 agonist. The docking experiments followed by molecular dynamics simulations and thermodynamic analysis led the drug design toward both the introduction of a lipophilic iodine and a flat pyridine/benzene at position 5 of the thiophene nucleus. Most of the synthesized compounds showed high TRPV1 efficacy and potency as well as selectivity. The molecular modeling analysis highlighted crucial hydrophobic interactions between Leu547 and the iodo-thiophene nucleus, as in amide 2a, or between Phe543 and the pyridinyl moiety, as in 3a. In the biological evaluation, both compounds showed protective properties against oxidative stress-induced ROS formation in human keratinocytes. Additionally, while 2a showed neuroprotective effects in both neurons and rat brain slices, 3a exhibited potent antinociceptive effect in vivo..

Chemodivergent Photocatalyzed Heterocyclization of Hydrazones and Isothiocyanates for the Selectivity Synthesis of 2-Amino-1,3,4-thiadiazoles and 1,2,4-Triazole-3-thiones

A photocatalytic chemodivergent reaction for the selectivity formation of C-S and C-N bonds in a controlled manner was proposed. The reaction medium, either neutral or acidic, is critical to dictate the formation of 2-amino-1,3,4-thiadiazoles and 1,2,4-triazole-3-thiones from isothiocyanates and hydrazones. This is a practical protocol to achieve the chemoselectivity under mild and metal-free conditions.

Palladium-Catalyzed Selective Amino- and Alkoxycarbonylation of Iodoarenes with Aliphatic Aminoalcohols as Heterobifunctional O,N-Nucleophiles

Palladium-catalyzed amino- and alkoxycarbonylation reactions of aryl iodides were investigated in the presence of aliphatic heterobifunctional N,O-nucleophiles. Selective synthesis of amide alcohols and amide esters was realized, controlled by the base and substrate ratio. The effect of iodobenzene substituents was also studied with surprising results in terms of product selectivity. In addition to the model ethanolamine/iodobenzene system, various heteroaromatic substrates and numerous related nucleophiles were tested under optimized conditions, providing moderate to good yields of the target compounds. Reactions of serinol and 1,3-diamino-2-propanol as model trifunctional compounds showed particularly high chemoselectivity on amide ester products. Considering the coordinative properties of the applied nucleophiles, a rational catalytic cycle was proposed.

Hydrogen-free palladium-catalyzed intramolecular anti-Markovnikov hydroaminocarbonylation of 2-(1-methylvinyl)anilines

The palladium-catalyzed intramolecular hydroaminocarbonylation of 2-(1-methylvinyl)aniline derivatives has been achieved using dppp (1,3-bis(diphenylphosphino)propane) as a ligand under hydrogen-free conditions. The reaction involves the generation of an active palladium hydride species with a catalytic amount of TsOH. This amide bond formation reaction was applied to the synthesis of various 4-substituted 3,4-dihydroquinolone derivatives with both high yield and regioselectivity.

Pd-Catalyzed Asymmetric 5-exo-trig Cyclization/Cyclopropanation/Carbonylation of 1,6-Enynes for the Construction of Chiral 3-Azabicyclo[3.1.0]hexanes

We herein disclose a mild and efficient access to chiral 3-azabicyclo[3.1.0]hexanes via a Pd-catalyzed asymmetric 5-exo-trig cyclization/cyclopropanation/carbonylation of 1,6-enynes. Various nucleophiles, such as alcohols, phenols, amines and water, are well compatible with the reaction system. This reaction forms three C-C bonds, two rings, two adjacent quaternary carbon stereocenters as well as one C-O/C-N bond with excellent regio- and enantioselectivities. The products could be further functionalized to generate a library of 3-azabicyclo[3.1.0]hexane frameworks.

Enantioselective Hydrocarbamoylation of Alkenes

The asymmetric hydroaminocarbonylation of olefins represents a straightforward approach for the synthesis of enantioenriched amides, but is hampered by the necessity to employ CO gas, often at elevated pressures. We herein describe, as an alternative, an enantioselective hydrocarbamoylation of alkenes leveraging dual copper hydride and palladium catalysis to enable the use of readily available carbamoyl chlorides as a practical carbamoylating reagent. The protocol is applicable to various types of olefins, including alkenyl arenes, terminal alkenes, and 1,1-disubstituted alkenes. Substrates containing a diverse range of functional groups as well as heterocyclic substructures undergo functionalization to provide α- and β-chiral amides in good yields and with excellent enantioselectivities.

Palladium-Catalyzed Regio- and Stereoselective Hydroaminocarbonylation of Unsymmetrical Internal Alkynes toward α,β-Unsaturated Amides

α,β-Unsaturated amides play a vital role in natural products, pharmaceuticals, organic synthesis, and functional materials. Herein, we disclosed a regio- and stereoselective hydroaminocarbonylation of unsymmetrical internal alkynes via palladium catalysis to synthesize α,β-unsaturated amides. This protocol features excellent regio- and exclusive (E)-stereoselectivity, high atom and step-economy, broad substrate scope, and functional group tolerance.

Copper-Catalyzed Substrate-Controlled Carbonylative Synthesis of α-Keto Amides and Amides from Alkyl Halides

Controllable production of α-keto amides and amides from the same substrates is an attractive goal in the field of transition-metal-catalyzed (double-)carbonylation. Herein, a novel copper-catalyzed highly selective double carbonylation of alkyl bromides has been developed. Moderate to good yields of α-keto amides were obtained as the only products. In the case of alkyl iodides, double- and mono-carbonylation can be achieved controllably under different conditions.

Catalyst-controlled selective borocarbonylation of benzylidenecyclopropanes: regiodivergent synthesis of γ-vinylboryl ketones and β-cyclopropylboryl ketones

Regioselective catalytic multi-functionalization reactions enable the rapid synthesis of complexed products from the same precursors. In this communication, we present a method for the regiodivergent borocarbonylation of benzylidenecyclopropanes with aryl iodides. Various γ-vinylboryl ketones and β-cyclopropylboryl ketones were produced in moderate to good yields with excellent regioselectivity from the same substrates. The choice of the catalyst is key for the regioselectivity control: γ-vinylboryl ketones were produced selectively with IPrCuCl and Pd(dppp)Cl₂ as the catalytic system, while the corresponding β-cyclopropylboryl ketones were obtained in high regioselectivity with Cu(dppp)Cl, [Pd(η³-cinnamyl)Cl]₂ and xantphos as the catalytic system. Moreover, γ-vinylboryl ketones and β-cyclopropylboryl ketones were successfully transformed into several other value-added products.

A novel procedure for regiodivergent borocarbonylation of benzylidenecyclopropanes has been developed. A variety of valuable γ-vinylboryl ketones and β-cyclopropylboryl ketones can be obtained selectively in excellent yields.

Palladium-catalyzed enantioselective carbonylation reactions

Carbonylation, one of the most powerful approaches to the preparation of carbonylated compounds, has received significant attention from researchers active in various fields. Indeed, impressive progress has been made on this subject over the past few decades. Among the various types of carbonylation reactions, asymmetric carbonylation is a straightforward methodology for constructing chiral compounds. Although rhodium-catalyzed enantioselective hydroformylations have been discussed in several elegant reviews, a general review on palladium-catalyzed asymmetric carbonylations is still missing. In this review, we summarize and discuss recent achievements in palladium-catalyzed asymmetric carbonylation reactions. Notably, this review’s contents are categorized by reaction type.

Palladium-Catalyzed Tandem Hydrocarbonylative Lactamization and Cycloaddition Reaction for the Construction of Bridged Polycyclic Lactams

The intramolecular hydroaminocarbonylation of alkenes is a compelling tool to rapidly access lactam, a privileged motif ubiquitous in natural products, pharmaceuticals, and agrochemicals. However, selective carbonylation to bridged polycyclic lactams with a lactam nitrogen at a bridgehead position is less explored. We herein report a modular palladium-catalyzed approach to perform a tandem hydrocarbonylative lactamization/Diels-Alder cycloaddition reaction with 2-vinyl aryl aldimines, alkenes, and CO, which offers convenient access to furnish the bridged polycyclic lactams in high yields with high selectivities.

Origin of Ligand Effects on Stereoinversion in Pd-Catalyzed Synthesis of Tetrasubstituted Olefins

The mechanism and origin of ligand effects on stereoinversion of Pd-catalyzed synthesis of tetrasubstituted olefins were investigated using DFT calculations and the approach of energy decomposition analysis (EDA). The results reveal that the stereoselectivity-determining steps are different when employing different phosphine ligands. This is mainly due to the steric properties of ligands. With the bulkier Xantphos ligand, the syn/anti-to-Pd 1,2-migrations determine the stereoselectivity. While using the less hindered P(o-tol)₃ ligand, the 1,3-migration is the stereoselectivity-determining step. The EDA results demonstrate that Pauli repulsion and polarization are the dominant factors for controlling the stereochemistry in 1,2- and 1,3-migrations, respectively. The origins of differences of Pauli repulsion and polarization between the two stereoselective transition states are further identified.

Divergent Aminocarbonylations of Alkynes Enabled by Photoredox/Nickel Dual Catalysis

A metallaphotoredox-catalyzed strategy for the selective and divergent aminocarbonylation of alkynes with amines and 1 atm of CO is reported. This synergistic protocol not only enables the Markovnikov-selective hydroaminocarbonylation of alkynes to afford α,β-unsaturated amides, but also facilitates a sequential four-component hydroaminocarbonylation/radical alkylation in the presence of tertiary and secondary alkyl boronate esters, which allows for straightforward conversion of alkynes into corresponding amides. Preliminary mechanistic studies disclose that a photoinduced oxidative insertion of aniline and CO into nickel followed by a migratory insertion of (carbamoyl)nickel species could be involved.

Copper-catalyzed enantioselective carbonylation toward α-chiral secondary amides

Secondary amides are omnipresent structural motifs in peptides, natural products, pharmaceuticals, and agrochemicals. The copper-catalyzed enantioselective hydroaminocarbonylation of alkenes described in this study provides a direct and practical approach for the construction of α-chiral secondary amides. An electrophilic amine transfer reagent possessing a 4-(dimethylamino)benzoate group was the key to the success. This method also features broad functional group tolerance and proceeds under very mild conditions, affording a set of α-chiral secondary amides in high yields (up to 96% yield) with unprecedented levels of enantioselectivity (up to >99% ee). α,β-Unsaturated secondary amides can also be produced though the method by using alkynes as the substrate.

Double-Regiodetermining-Stages Mechanistic Model Explaining the Regioselectivity of Pd-Catalyzed Hydroaminocarbonylation of Alkenes with Carbon Monoxide and Ammonium Chloride

Pd-catalyzed hydroaminocarbonylation (HAC) of alkenes with CO and NH₄Cl enables atom-economic and regiodivergent synthesis of primary amides, but the origin of regioselectivity was incorrectly interpreted in previous computational studies. A density functional theory study was performed herein to investigate the mechanism. Different from the previous proposals, both alkene insertion and aminolysis were found to be potential regioselectivity-determining stages. In the alkene insertion stage, 2,1-insertion is generally faster than 1,2-insertion irrespective of neutral or cationic pathways for both P(^tBu)₃ and xantphos. Such selectivity results from the unconventional proton-like hydrogen of the Pd-H bond in alkene insertion transition states. For less bulky alkenes, aminolysis with P(^tBu)₃ shows low selectivity, while linear selectivity dominates in this stage with xantphos due to a stronger repulsion between xantphos and branched acyl ligands. It was further revealed that the less-mentioned CO concentration and solvents also influence the regioselectivity by adjusting the relative feasibilities of CO-involved steps and NH₃ release from ammonium chloride, respectively. The presented double-regiodetermining-stages mechanistic model associated with the effects of ligands, CO concentration, and solvents well reproduced the experimental selectivity to prove its validity and illuminated new perspectives for the regioselectivity control of HAC reactions.

Ligand-Controlled Regiodivergent Thiocarbonylation of Alkynes toward Linear and Branched α,β-Unsaturated Thioesters

Thiocarbonylation of alkynes offers an ideal procedure for the synthesis of unsaturated thioesters. A robust ligand-controlled regioselective thiocarbonylation of alkynes is developed. Utilizing boronic acid and 5-chlorosalicylic acid as the acid additive to in situ form 5-chloroborosalicylic acid (5-Cl-BSA), and bis(2-diphenylphosphinophenyl)ether (DPEphos) as the ligand, linear α,β-unsaturated thioesters were produced in a straightforward manner. Switching the ligand to tri(2-furyl)phosphine can turn the reaction selectivity to give branched products. Remarkably, this approach also represents the first example on thiocarbonylation of internal alkynes.

Palladium-Catalyzed Markovnikov Hydroaminocarbonylation of 1,1-Disubstituted and 1,1,2-Trisubstituted Alkenes for Formation of Amides with Quaternary Carbon

Hydroaminocarbonylation of alkenes is one of the most promising yet challenging methods for the synthesis of amides. Herein, we reported the development of a novel and effective Pd-catalyzed Markovnikov hydroaminocarbonylation of 1,1-disubstituted or 1,1,2-trisubstituted alkenes with aniline hydrochloride salts to afford amides bearing an α quaternary carbon. The reaction makes use of readily available starting materials, tolerates a wide range of functional groups, and provides a facile and straightforward approach to a diverse array of amides bearing an α quaternary carbon. Mechanistic investigations suggested that the reaction proceeded through a palladium hydride pathway. The hydropalladation and CO insertion are reversible, and the aminolysis is probably the rate-limiting step.

Heteroditopic Macrobicyclic Molecular Vessels for Single Step Aerial Oxidative Transformation of Primary Alcohol Appended Cross Azobenzenes

A series of oxy-ether tris-amino heteroditopic macrobicycles (L1-L4) with various cavity dimensions have been synthesized and explored for their Cu(II) catalyzed selective single step aerial oxidative cross-coupling of primary alcohol based anilines with several aromatic amines toward the formation of primary alcohol appended cross azobenzenes (POCABs). The beauty of this transformation is that the easily oxidizable benzyl/primary alcohol group remains unhampered during the course of this oxidation due to the protective oxy-ether pocket of this series of macrobicyclic vessels. Various dimensionalities of the molecular vessels have shown specific size complementary selection for substrates toward efficient syntheses of regioselective POCAB products. To establish the requirement of the three-dimensional cavity based additives, a particular catalytic reaction has been examined in the presence of macrobicycles (L2 and L3) versus macrocycles (MC1 and MC2) and tripodal acyclic (AC1 and AC2) analogous components, respectively. Subsequently, L1-L4 have been extensively utilized toward the syntheses of as many as 44 POCABs and are characterized by different spectroscopic techniques and single crystal X-ray diffraction studies.

Ligand-Controlled Copper-Catalyzed Regiodivergent Carbonylative Synthesis of α-Amino Ketones and α-Boryl Amides from Imines and Alkyl Iodides

Regioselective transformation is among the long-standing challenges in organic synthesis. In this communication, a copper-catalyzed selectivity controlled regiodivergent borocarbonylation of imines with alkyl iodides has been developed. Various α-amino ketones and α-boryl amides were produced in moderate to good yields from the same substrates. The choice of the ligand is key for the regioselectivity control: α-amino ketones were produced selectively in good yields with (p-CF₃ C₆ H₄ )₃ P as the ligand, whereas the corresponding α-boryl amides were obtained with high regioselectivities when using ^Me IMes as the ligand.

A General and Highly Selective Palladium-Catalyzed Hydroamidation of 1,3-Diynes

A chemo-, regio-, and stereoselective mono-hydroamidation of (un)symmetrical 1,3-diynes is described. Key for the success of this novel transformation is the utilization of an advanced palladium catalyst system with the specific ligand Neolephos. The synthetic value of this general approach to synthetically useful α-alkynyl-α, β-unsaturated amides is showcased by diversification of several structurally complex molecules and marketed drugs. Control experiments and density-functional theory (M06L-SMD) computations also suggest the crucial role of the substrate in controlling the regioselectivity of unsymmetrical 1,3-diynes.

Atroposelective carbonylation of aryl iodides with amides: facile synthesis of enantioenriched cyclic and acyclic amides

An unprecedented palladium-catalyzed asymmetric carbonylation of ArI with carbon monoxide (CO) to expand a class of atroposelective cyclic and acyclic amides in good yields with high enantioselectivities has been reported.

Mechanistic insights into the palladium-catalyzed hydroaminocarbonylation of alkenes

This study gives insights into the ligand-controlled regioselectivity of the palladium catalyzed aminocarbonylation of alkenes with CO and ammonia.

Organocatalytic aminocarbonylation of α,β-unsaturated ketones with N,N-dimethyl carbamoylsilane

Schwesinger's superbase can efficiently activate the Si–CONMe₂ bond and initiate the aminocarbonylation of α,β-unsaturated ketones and N,N-dimethyl carbamoylsilane.

Selective Synthesis of Pyrano[3,2-b]indoles or Cyclopenta[b]indoles Tethered with Medium-Sized Rings via Cascade C-C σ-Bond Cleavage and C-H Functionalization

Highly atom-economical tandem reactions have been developed for the synthesis of pyrano[3,2-b]indoles or cyclopenta[b]indoles tethered with 7-, 8-, or 9-membered rings. These reactions first undergo a carbon-carbon σ-bond cleavage reaction of cyclic β-ketoesters. Next, in the presence of CuCl₂ and Ag₂CO₃, intramolecular O-H/C-H coupling occurs to give pyrano[3,2-b]indoles. This is the first example for capture of the enoloxyl radical of the intramolecular C-O bond formation reaction, whereas C3 nucleophilic addition afforded cyclopenta[b]indoles using TsOH·H₂O.

A direct synthesis of carboxylic acids via platinum-catalysed hydroxycarbonylation of olefins

A selective platinum-catalysed hydroxycarbonylation of aliphatic olefins has been achieved.