Redox-Neutral [4 + 2] Annulation of N-Methoxybenzamides with Alkynes Enabled by an Osmium(II)/HOAc Catalytic System

Chiral Osmium(II)/Salox Species Enabled Enantioselective γ-C(sp3)-H Amidation: Integrated Experimental and Computational Validation For the Ligand Design and Reaction Development

Herein, multiple types of chiral Os(II) complexes have been designed to address the appealing yet challenging asymmetric C(sp3)-H functionalization, among which the Os(II)/Salox species is found to be the most efficient for precise stereocontrol in realizing the asymmetric C(sp3)-H amidation. As exemplified by the enantioenriched pyrrolidinone synthesis, such tailored Os(II)/Salox catalyst efficiently enables an intramolecular site-/enantioselective C(sp3)-H amidation in the γ-position of dioxazolone substrates, in which benzyl, propargyl and allyl groups bearing various substituted forms are well compatible, affording the corresponding chiral γ-lactam products with good er values (up to 99 : 1) and diverse functionality (>35 examples). The unique performance advantage of the developed chiral Os(II)/Salox system in terms of the catalytic energy profile and the chiral induction has been further clarified by integrated experimental and computational studies.

A Strategy for Site- and Chemoselective C-H Alkenylation through Osmaelectrooxidative Catalysis

Herein, we disclose osmaelectrocatalyzed C-H activations that set the stage for electrooxidative alkyne annulations by benzoic acids. The osmium electrocatalysis enables site- and chemoselective electrooxidative C-H activations with unique levels of selectivity. The isolation of unprecedented osmium(0) and osmium(II) intermediates, along with crystallographic characterization and analyses by spectrometric and spectroscopic in operando techniques delineate a synergistic osmium redox catalyst regime. Detailed mechanistic studies revealed a facile C-H cleavage, which allows for an ample substrate scope, providing provide robust and user-friendly access to annulated heterocycles.

Redox-Neutral Rhodium(III)-Catalyzed Chemospecific and Regiospecific [4+1] Annulation between Indoles and Alkenes for the Synthesis of Functionalized Imidazo[1,5-a]indoles

Exploiting internal alkenes embedded with an oxidizing function/leaving group as a rare and unconventional one-carbon unit, a redox-neutral rhodium(III)-catalyzed chemo- and regiospecific [4+1] annulation between indoles and alkenes for the synthesis of functionalized imidazo[1,5-a]indoles has been achieved. Internal alkenes employed here can fulfill an unusual [4+1] annulation rather than normal [4+2] annulation/C-H alkenylation. This method is characterized by excellent chemo- and regioselectivity, broad substrate scope, good functional group tolerance, good to high yields, and redox-neutral conditions.

Mechanistic Insights into the Dual Directing Group-Mediated C-H Functionalization/Annulation via a Hydroxyl Group-Assisted MIII-MV-MIII Pathway

The experimental investigations on the catalyst [Cp*Rh(OAc)₂ and Cp*Ir (OAc)₂)]-controlled [3 + 2] and [4 + 2] annulations of oximes with propargyl alcohols have been finished in our previous work and a supposed dual directing group-mediated reaction pathway has been deduced for the chemodivergent product synthesis. However, the detailed interaction modes of the dual directing groups binding with the corresponding metal center to achieve the above observed chemoselectivity remain unclear and even contradict. For instance, the calculational traditional dual direct coupling transition states suggested that both Cp*Rh(OAc)₂- and Cp*Ir(OAc)₂-catalyzed reactions would generate five-membered indenamines as the dominant products via [3 + 2] annulation. To address this concern, herein, systematic DFT calculations combined with proof-of-concept experiments have been carried out. Accordingly, a novel and more favorable M^III-M^V-M^III reaction mechanism, which involves an unprecedented HOAc together with a hydroxyl group-assisted reaction pathway in which the hydroxyl group acts as double effectors for the formation of M-O coordination and [MeO···H···O(CCH₃)O···H···O] bonding interactions, was deduced. Taken together, the present results would provide a rational basis for future development of the dual directing group-mediated C-H activation reactions.

Arene-Osmium(II) Complexes in Homogeneous Catalysis

Although the application of arene-osmium(II) complexes in homogeneous catalysis has been much less studied than that of their ruthenium analogues, different works have shown that, in some instances, a comparable or even superior effectiveness can be achieved with this particular class of compounds. This review article focuses on the catalytic applications of arene-osmium(II) complexes. Among others, transfer hydrogenation, hydrogenation, oxidation, and nitrile hydration reactions, as well as different C-C bond forming processes, are comprehensively discussed.

Synthesis of 1-Benzyl-, 1-Alkoxyl-, and 1-Aminoisoquinolines via Rhodium(III)-Catalyzed Aryl C-H Activation and Alkyne Annulation

One-pot syntheses of 1-benzyl-, 1-alkoxyl-, and 1-alkylamino- isoquinolines through automatic directing group (DG^auto)-assisted, rhodium(III)-catalyzed aryl C-H activation and annulation with internal alkynes were developed. The reactions affording 1-benzylisoquinolines involve a cascade oximation of diarylacetylenes with hydroxylamine, forming aryl benzyl ketone oxime, and oxime-assisted rhodium(III)-catalyzed aryl C-H activation and followed annulation with another molecule of diarylacetylene in a one-pot manner. The formation of 1-alkoxyl/amino isoquinolines includes the addition of nucleophilic alcohols or amines to aryl nitriles, imine-assisted rhodium-catalyzed aryl C-H activation, and subsequent alkyne annulation.

Crystal structure of 4-ethyl-3-phenylisoquinolin-1(2H)-one, C17H15NO

C17H15NO, monoclinic, C2/c (no. 15), a = 19.197(2) Å, b = 8.0719(8) Å, c = 16.6511(18) Å, α = 90°, β = 100.171(10)°, γ = 90°,V = 2539.6(5) Å3, Z = 8, R gt (F) = 0.0416, wR ref (F 2) = 0.1107, T = 100(1) K.

CCDC no.: 2020262

Rhodium(iii)-catalyzed C–H activation/annulation of N-iminopyridinium ylides with alkynes and diazo compounds

Rh(iii)-Catalyzed C–H activation/annulation of N-iminopyridinium ylides with alkynes and diazo compounds has been realized for the synthesis of isoquinolones and isocoumarins.

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.

γ-Carboline synthesis enabled by Rh(iii)-catalysed regioselective C-H annulation

A redox-neutral Rh(iii)-catalyzed C-H annulation of indolyl oximes was developed. Relying on the use of various alkynyl silanes as the terminal alkyne surrogates, the reaction exhibited a reverse regioselectivity, thus giving an exclusive and easy way for the synthesis of a wide range of substituent free γ-carbolines at C3 position with high efficiency. Deuterium-labelling experiments and kinetic analysis have preliminarily shed light on the working mode of this catalytic system.

Isoquinolone Synthesis via Zn(OTf)2-Catalyzed Aerobic Cyclocondensation of 2-(1-Alkynyl)-benzaldehydes with Arylamines

A zinc(II) triflate-catalyzed cyclocondensation of ortho-alkynylbenzaldehydes with arylamines in the presence of base under an oxygen atmosphere affording isoquinolones in good to high yields has been developed. The advantages of the present catalyst system include the use of an air-stable and cheap commercially available Lewis acid as the catalyst, high atom utilization and easily available starting materials.

Synthesis of isoquinolones by visible-light-induced deaminative [4+2] annulation reactions

A metal-free approach for the synthesis of isoquinolone derivatives by means of photoinitiated deaminative [4+2] annulation of alkynes and N-amidepyridinium salts is presented.