Rhodium(III)-Catalyzed C–H Functionalization in Water for Isoindolin-1-one Synthesis

Copper-catalyzed asymmetric 1,2-arylboration of enamines: access to chiral borate-containing 3,3'-disubstituted isoindolinones

An enantioselective copper-catalyzed 1,2-arylboration reaction of enamines has been developed by employing (R)-xyl-BINAP as a chiral ligand. A number of chiral borate-containing 3,3'-disubstituted isoindolinones were obtained in moderate to good yields and good to excellent enantioselectivities from the reactions of N-(o-iodobenzoyl)enamines and bis(pinacolato)diboron (B2pin2) under mild reaction conditions. Synthetic transformations of the products were conducted to demonstrate the practicality of this reaction.

DFT Study on the Mechanisms and Selectivities in Rh (III)-Catalyzed [5 + 1] Annulation of 2-Alkenylanilides and 2-Alkylphenols with Allenyl Acetates

The mechanisms and regio-, chemo-, and stereoselectivity were theoretically investigated in the Rh(III)-catalyzed [5 + 1] annulation of 2-alkenylanilides and 2-alkylphenols with allenyl acetates. Two different reactants, 2-alkenylanilides and 2-alkylphenols, were selected as model systems in the density functional theory calculations. The obtained theoretical results show that both these reactants exhibit similar steps, namely, (1) N-H/O-H deprotonation and C-H activation, (2) allenyl acetate migratory insertion, (3) β-oxygen elimination, (4) intramolecular nucleophilic addition of the nitrogen/oxygen-rhodium bond resulting in [5 + 1]-annulation, and (5) protonation with the formation of the desired product and regeneration of the Rh(III) catalyst. The theoretical evidence suggests that the selectivity is determined at the step of allenyl acetate's migratory insertion. Moreover, the regioselectivity is driven by electronic effects, while the interaction energies (C-H···π and C-H···O interactions) play a more imperative role in controlling the stereoselectivity. The obtained theoretical results not only well rationalize the experimental observations but also provide important mechanistic insights for related types of [5 + 1]-annulation reactions.

Rh(III)-Catalyzed [4 + 1] Annulation of Benzamides with Vinyl Cyclic Carbonates for the Synthesis of Isoindolinones

A Rh(III)-catalyzed C-H bond activation and subsequent [4+1] annulation of benzamides with vinyl cyclic carbonates have been developed for the synthesis of isoindolinones, in which the electron-rich alkenes could serve as one-carbon units. This reaction proceeds smoothly with high regioselectivity under oxidant- and silver-free conditions and exhibits broad substrate scope and functional group tolerance including some biological active materials. The scale-up reaction and derivatizations of the product further demonstrate the potential synthetic utility of this transformation.

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.

Merging Rh-Catalyzed C-H Functionalization and Cascade Cyclization to Enable Propargylic Alcohols as Three-Carbon Synthons

Reported herein is a reactivity of propargyl alcohols as "Three-Carbon Synthons" in a Rh(III)-catalyzed C-H functionalization of acetanilides, leading to the synthesis of core structures of isocryptolepine, γ-carbolines, dihydrochromeno[2,3-b]indoles, and diindolylmethanes (DIM) derivatives. The transformation involves a rhodium(III)-catalyzed C-H functionalization and heteroannulation to yield indoles followed by a cascade cyclization with both external and internal nucleophiles to afford diverse products. The role of the hydroxy group, the key function of the silver additive, the origin of the reverse regioselectivity and the rate-determining step, are rationalized in conformity with the combination of experimental, noncovalent interaction analysis and DFT studies. This protocol is endowed with several salient features, including one-pot multistep cascade approach, exclusive regioselectivity, good functional group tolerance and synthesis of variety of molecular frameworks.

Divergent Reactivity of Phosphorylated and Related Allenes: [4 + 2] Cycloaddition with 3,6-Diphenyltetrazine, Self-Addition Leading to Dimers and [Pd]-Complex Formation

Phosphorus-based naphthalenes are formed by self-dimerization-cum-cyclization of α-aryl allenylphosphonates or allenylphosphine oxides using catalytic Pd(OAc)₂in the presence of PPh₃ and Et₃N . This reaction involves [4 + 2]-cycloaddition with the (β,γ) double bond of one allene as the dienophile; the double bonds at the α-aryl-(β',γ') group and (α,β)-carbons of the second allene act as the diene part. A subsequent proton shift also takes place. Upon treating allenylphosphine oxides with Pd(OAc)₂ [stoichiometry 2:1] in the presence of PPh₃/Ag₂CO₃, a [Pd]-complex is isolated and structurally characterized. This complex can be used as a catalyst for C-C bond-forming reactions of phosphorus-based allenes with 2-iodophenol. Densely substituted 3,6-diphenylpyridazines are conveniently obtained in excellent yields by a thermally induced regioselective Inverse Electron Demand Diels-Alder (IEDDA) reaction of allenes with 3,6-diphenyltetrazine, followed by a [1,3]-H shift.

Magnetic chitosan stabilized Cu(II)-tetrazole complex: an effective nanocatalyst for the synthesis of 3-imino-2-phenylisoindolin-1-one derivatives under ultrasound irradiation

In the present research, a recyclable catalyst has been prepared via a simple approach using chitosan as a linear polysaccharide. This paper reports the synthesis of novel copper(II) complex of 5-phenyl-1H-tetrazole immobilized on magnetic chitosan (MCS@PhTet@Cu(II)) as an effective catalyst. Transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), vibrating sample magnetometer (VSM), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and inductively coupled plasma mass spectrometry (ICP-MS) techniques were applied for the characterization of the catalyst. The catalytic activity of MCS@PhTet@Cu(II) was evaluated in the ultrasound-assisted synthesis of 3-imino-2-phenylisoindolin-1-one derivatives via the reaction between benzoyl chloride and arylcyanamides in ethanol at ambient temperature. Utilizing a wide variety of arylcyanamides under mild conditions, no use of toxic organic solvents, moderate reaction time, high yields along with catalyst excellent reusability and easy separation of the products without any tedious separation techniques, made this method a novel and simple process. The resulting heterogeneous catalyst showed valuable advantages such as easier work-up, better stability, and greater separation ability using an external magnet. The catalyst showed high efficacy and recyclability even after five cycles with no significant loss of its efficacy. The present methodology provides a path for the preparation of structurally diverse heterocyclic compounds, which may exhibit important biological activity.

Cp*Rh(III)-catalyzed and solvent-controlled tunable [4+1]/[4+3] annulation for the divergent assembly of dihydrobenzo[cd]indoles and dihydronaphtho[1,8-bc]azepines

Chemo- and regioselectively Cp*Rh-catalyzed tunable [4+1]/[4+3] cyclization of free 1-naphthylamines with propargyl carbonates has been accomplished by regulating the reaction solvents. The reaction allowed a variety of dihydrobenzo[cd]indoles and dihydronaphtho[1,8-bc]azepines...

Redox-neutral rhodium(III)-catalyzed chemo- and regiospecific [4 + 1] annulation between benzamides and alkenes for the synthesis of functionalized isoindolinones

Herein, using electron-deficient alkenes embedded with an oxidizing function/leaving group as a rare and nontraditional C₁ synthon, we have achieved the redox-neutral Rh(III)-catalyzed chemo- and regioselective [4 + 1] annulation of benzamides for the synthesis of functionalized isoindolinones. This method features broad substrate scope, good to excellent yields, excellent chemo- and regioselectivity, good tolerance of functional groups and mild external-oxidant-free conditions.

Easy synthesis of imidazo[1,5-a]indol-3-ones through Rh(III)-catalyzed C-H allenylation/annulation

A highly efficient and regioselective synthesis of imidazo[1,5-a]indol-3-ones has been developed via a sequential C-H allenylation/annulation starting from easily available N-methoxycarbamoyl indoles and propargyl alcohols, in which the propargyl alcohols served as a C1 synthon. This strategy displays excellent regioselectivity, high atom economy and tolerates a broad substrate scope.

Stereoselective rhodium-catalyzed 2-C-H 1,3-dienylation of indoles: dual functions of the directing group

A rhodium-catalyzed intermolecular highly stereoselective 1,3-dienylation at the 2-position of indoles with non-terminal allenyl carbonates has been developed by using 2-pyrimidinyl or pyridinyl as the directing group. The reaction tolerates many functional groups affording the products in decent yields under mild conditions. In addition to C-H bond activation, the directing group also played a vital role in the determination of Z-stereoselectivity for the C-H functionalization reaction with 4-aryl-2,3-allenyl carbonates, which is confirmed by the E-selectivity observed with 4-alkyl-2,3-allenyl carbonates. DFT calculations have been conducted to reveal that π-π stacking involving the directing 2-pyrimidinyl or pyridinyl group is the origin of the observed stereoselectivity. Various synthetic transformations have also been demonstrated.

Ru(II)-catalyzed allenylation and sequential annulation of N-tosylbenzamides with propargyl alcohols

We hereby report Ru(ii)-catalyzed C(sp2)-H allenylation of N-tosylbenzamides to access multi-substituted allenylamides. Furthermore, the allenylamides were converted to the corresponding isoquinolone derivatives via base mediated annulation. The current protocol features low catalyst loading, mild reaction conditions, high functional group compatibility and desired scalability. The unique functionality of the afforded allenes allowed further transformations to expand the practicality of the protocol.

Isoindolinone Synthesis via One-Pot Type Transition Metal Catalyzed C-C Bond Forming Reactions

Isoindolinone structure is an important privileged scaffold found in a large variety of naturally occurring as well as synthetic, biologically and pharmaceutically active compounds. Owing to its crucial role in a number of applications, the synthetic methodologies for accessing this heterocyclic skeleton have received significant attention during the past decade. In general, the synthetic strategies can be divided into two categories: First, direct utilization of phthalimides or phthalimidines as starting materials for the synthesis of isoindolinones; and second, construction of the lactam and/or aromatic rings by different catalytic methods, including C-H activation, cross-coupling, carbonylation, condensation, addition and formal cycloaddition reactions. Especially in the last mentioned, utilization of transition metal catalysts provides access to a broad range of substituted isoindolinones. Herein, the recent advances (2010-2020) in transition metal catalyzed synthetic methodologies via formation of new C-C bonds for isoindolinones are reviewed.

Ruthenium-catalysed C–H/C–N bond activation: facile access to isoindolinones

A facile ruthenium-catalysed C–H/C–N bond activation and the subsequent annulation of readily available benzoic acids with in situ generated formaldimines are developed for the efficient synthesis of a wide range of biologically important isoindolinones.

Palladium-catalyzed dehydrogenative C–H cyclization for isoindolinone synthesis

In this paper Pd-catalyzed intramolecular dehydrogenative C(sp³)–H amidation for the synthesis of isoindolinones is described. This method features the use of a Pd/C catalyst and the addition of a stoichiometric amount of oxidant is not necessary. A mechanistic study suggested the possible formation of H₂ gas during the reaction.

Pd-catalyzed intramolecular dehydrogenative C(sp³)–H amidation for the synthesis of isoindolinones was developed. Use of Pd/C as a catalyst enables the desired cyclization to proceed smoothly without adding any stoichiometric oxidants.

Green strategies for transition metal-catalyzed C–H activation in molecular syntheses

Sustainable strategies for the activation of inert C–H bonds towards improved resource-economy.

Lossen Rearrangement vs C-N Reductive Elimination Enabled by Rh(III)-Catalyzed C-H Activation/Selective Lactone Ring-Opening: Chemodivergent Synthesis of Quinolinones and Dihydroisoquinolinones

An unprecedented Rh(III)-catalyzed cascade C-H activation/Lossen rearrangement of aromatic amides with methyleneoxetanones has been realized along with a tunable C-N bond reductive elimination/trans esterification, giving divergent access to quinolinones and dihydroisoquinolinones via selective ring-opening of the four-membered lactone unit. Combined computational and experimental mechanistic studies defined the solvent-involved distinguished reaction paths, the origin of the observed chemodivergence, as well as the role of the substituent attached at the oxidizing directing group in tuning the reaction outcomes.

Ru(II)-Catalyzed and acidity-controlled tunable [5+1]/[5+2] annulation for building ring-fused quinazolines and 1,3-benzodiazepines

The Ru(ii)-catalyzed tunable [5+1]/[5+2] annulation of N-benzo[d]imidazole indolines with propargyl carbonates has been realized for the divergent synthesis of ring-fused quinazolines and 1,3-benzodiazepines bearing various functional groups. These transformations represent an efficient and practical strategy in constructing complex heterocycles via diversified C-H functionalization. A distinctive acidity-controlled reaction manner has been clarified to account for the chemoselectivity.

Rh(III)-Catalyzed Redox-Neutral [4+2] Annulation for Direct Assembly of 3-Acyl Isoquinolin-1(2H)-ones as Potent Antitumor Agents

By virtue of an efficient rhodium(III)-catalyzed redox-neutral C-H activation/ring-opening of a strained ring/[4+2] annulation cascade of N-methoxybenzamides with propargyl cycloalkanols, diverse 3-acyl isoquinolin-1(2H)-ones were directly obtained in good yields and with excellent functional group compatibility. Additionally, their antitumor activities against various human cancer cells including HepG2, A549, MCF-7 and SH-SY5Y were evaluated and the action mechanism of the selected compound was also investigated in vitro. The results revealed that these products possessed a potent efficacy, by inhibiting proliferation and inducing apoptosis in a time-dependent and dose-dependent manner, suggesting that such compounds can serve as promising candidates for anti lung cancer drug discovery.

Tin Powder-Promoted Cascade Condensation/Allylation/Lactamization: Synthesis of Isoindolinones and Pyrazoloisoindol-8-ones

An efficient tin powder-promoted cascade condensation/allylation/lactamization of 2-formylbenzoic acids, hydrazides, and allyl bromides was developed for the synthesis of isoindolinones in good to excellent yields under mild conditions without any other additives or catalysts. Further manipulation of isoindolinones by iodocyclization process afforded the tricyclic tetrahydro-8 H-pyrazolo[5,1- a]isoindol-8-one derivatives, which could be converted into more complicated tetracyclic tetrahydro-4 H-azirino[1',2':2,3]pyrazolo[5,1- a]isoindol-4-ones.

Cu-Catalyzed SN2' Substitution of Propargylic Phosphates with Vinylarene-Derived Chiral Nucleophiles: Synthesis of Chiral Allenes

A new Cu-catalyzed enantioselective three-component (i.e., styrenes, B₂pin₂, and propargylic phosphates) allenylation via an S_N2' substitution of propargylic electrophiles with vinylarene-derived chiral nucleophiles is presented. This method provides an efficient and enantioselective approach to access a range of optically pure di-(1,1-), tri-, and tetra-substituted allenes with α-central chirality and axial chirality in excellent chemo-, regio-, diastereo-, and enantioselectivities.

Co(ii)/Cu(ii)-cocatalyzed oxidative C–H/N–H functionalization of benzamides with ketones: a facile route to isoindolin-1-ones

Co/Cu-cocatalyzed oxidative C–H/N–H annulation of amides with ketones is developed to synthesize isoindolin-1-ones.

Iridium(iii)-catalysed annulation of pyrazolidinones with propiolates: a facile route to pyrazolo[1,2-a] indazoles

Iridium(iii)-catalysed C–H bond activation/subsequent [4+1] cyclization for the synthesis of pyrazolo[1,2-a] indazoles has been developed.

Mild complexation protocol for chiral CpxRh and Ir complexes suitable for in situ catalysis

Mild complexations of chiral cyclopentadienes with rhodium(i) and iridium(i) precursors enable user-friendly in situ complex formation for catalytic applications.

A practical complexation method for chiral cyclopentadienyl (Cp^x) iridium and rhodium complexes is described. The procedure uses the free Cp^xH with stable and commercially available rhodium(i) and iridium(i) salts without base or additive. The conditions are mild and do not require the exclusion of air and moisture. A salient feature is the suitability for in situ complexations enhancing the user-friendliness of Cp^x ligands in asymmetric catalysis. DFT-calculations confirm an intramolecular proton abstraction pathway by either the bound acetate or methoxide. Furthermore, the superior facial selectivity of the proton abstraction step enabled the development of TMS-containing trisubstituted Cp^x ligands which display improved enantioselectivities for the benchmarking dihydroisoquinolone synthesis.

[Cp*RhIII ]/Ionic Liquid as a Highly Efficient and Recyclable Catalytic Medium for C-H Amidation

A [Cp*Rh^III ]-catalyzed direct C-H amidation is carried out in ionic liquid. Both C(sp² )-H bonds of (hetero)arenes and alkenes and unactivated C(sp³ )-H bonds can be easily amidated with high functional-group tolerance and excellent yields under these conditions. Notably, using [Cp*Rh^III ]/[BMIM]BF₄ (BMIM=1-butyl-3-methylimidazolium) as the green and recyclable medium is environmentally benign, in light of characteristics such as the reusability of the expensive rhodium catalyst, avoidance of highly toxic organic solvents, and mild reaction conditions, as well as a short reaction time.