Rhodium-Catalyzed Annulation of 4-Arylbut-3-yn-1-amines with Internal Alkynes through C–H Functionalization

Pd-Catalyzed Chelation-Assisted Regioselective and Site Selective Cyclative C-H Annulation of Alkynyl Oximes with Activated Alkynes

Electrophilic cyclization and concomitant C-H annulation constitute an expedient cascade strategy for the construction of multicyclic scaffolds with precise substitutional patterns. We report here a novel Pd-catalyzed cyclative annulation of ynone oxime with activated alkynes. The cascade features a dual regioselectivity including site selective C-H activation and chelation-assisted selective insertion of alkynes. Control experiments together with kinetic experiments give insights into the mechanism.

Pd-Catalyzed Sequential Electrophilic Cyclization/Selective C-H Annulation Cascade: Synthesis of Isoxazole-Phthalimide-Fused Poly-Heterocyclics

Harnessing the organo-palladium intermediates generated from electrophilic cyclizations for tandem C-C bond construction is a challenging task but constitutes an excellent tool for constructing complex motifs from simpler substrates. We realize herein such a cyclative annulation of alkynyl-oxime ethers with maleimides for the facile construction of isoxazole-phthalimide hybrid motifs through Pd(II) catalysis. This protocol features excellent regio-selectivity in C-H selection, a broad substrate scope, good functional group tolerance, and scalability. Necessary KIE & labeling studies give insight into the reaction mechanism.

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.

Visible light-assisted Ni-/Ir-catalysed atom-economic synthesis of spiro[furan-3,1'-indene] derivatives

An atom-economic, efficient, and highly convenient construction of spiro[furan-3,1'-indene] skeletons from isocyanides and 1,5-enynes by synergistic nickel- and iridium-photocatalysis is reported. Spirocyclization was developed under practical and mild conditions, which features excellent functional group tolerance, gram-scale synthesis and representative synthetic transformations for the obtained products and broad substrate scope. Primary mechanistic studies demonstrated that the reaction proceeds through energy-transfer-mediated excitation of intermediate catalytic species.

Platinum Iodide-Catalyzed Formal Three-Component Cascade Cycloaddition Reactions between γ-Aminoalkynes and Electron-Deficient Alkynes

Herein, we report a protocol for PtI₂-catalyzed formal three-component cascade cycloaddition reactions between γ-aminoalkynes and electron-deficient alkynes to afford highly substituted cyclohexadiene-b-pyrrolidines in good yields. On the basis of the results of the control experiments and density functional theory calculations, we present a plausible mechanism that proceeds via two key intermediates. The overall transformation involves the cleavage and formation of multiple C-C and C-N bonds and a previously unreported reaction mode of a seven-membered nitrogen heterocyclic intermediate.

Harnessing Rhodium-Catalyzed C-H Activation: Regioselective Cascade Annulation for Fused Polyheterocycles

In the realm of transition-metal catalyzed arene functionalization, rhodium(III) catalysis is considered as exemplary due to its propensity to activate C-H bonds to obtain comprehensive molecular assembly. Herein, we demonstrate a new rhodium(III) catalyzed assembly of polyheterocyclic scaffolds via C-H activation and regioselective annulation of 4-arylbut-3-yn-1-amines with 4-hydroxy-2-alkynoates. Heterocyclization and trans-metalation prior to annulation is the key for initiation of this relay redox-neutral catalytic cascade.

Recent Advances in Cycloaddition Reactions with Alkynes to Construct Heterocycles

Heterocyclic compounds, especially N-heterocycles and O-heterocycles, are prominent structural motifs present in numerous natural products and medically and/or economically important compounds. This review aims to describe the development of transition-metal-catalyzed cycloaddition reactions of functionalized m-atom partners with alkynes to access a wide range of five-, six-, and seven-membered heterocycles, that is functionalized N-heterocycles and O-heterocycles such as azepines, isoquinolines, isocoumarins, spiroheterocycles, indoles, furans, and pyrroles, in a selectively controlled manner with an emphasis on scope and limitations and with a discussion of the mechanisms.

1 Introduction

2 Intermolecular Cycloaddition To Construct Azepine Derivatives

2.1 [5+2] Cycloaddition

2.2 [3+2+2] Cycloaddition

2.3 [3+2]/[5+2] Cycloaddition

3 Intermolecular [4+2] Cycloaddition To Construct Isoquinolines or Isocoumarins

4 Intermolecular [3+2] Cycloaddition To Construct Spirohetero­cyclic Compounds, Indoles, Furans, and Pyrroles

5 Summary and Outlook

Rhodium(iii)-catalyzed diamidation of olefins via amidorhodation and further amidation

Rh(iii)/Co(iii)-catalyzed diamidation of amide-tethered olefins has been realized using dioxazolones and arylsulfonamides as different classes of amidating reagents.

Spiro[indene-1,4'-oxa-zolidinones] Synthesis via Rh(III)-Catalyzed Coupling of 4-Phenyl-1,3-oxazol-2(3H)-ones with Alkynes: A Redox-Neutral Approach

Transition-metal-catalyzed C-H activation synthesis of heterocyclic spiro[4,4]nonanes has persistently witnessed the use of additional stoichiometric transition-metal oxidant when employing C═C bond as the spiro ring closure site. Herein, we have addressed the issue by reporting a redox-neutral strategy for spiro[indene-1,4'-oxa-zolidinones] synthesis via Rh(III)-catalyzed coupling of 4-phenyl-1,3-oxazol-2(3H)-ones with alkynes. The synthesis features a broad substrate scope and high regiospecificity.

Construction of polycyclic bridged indene derivatives by a tandem 1,3-rearrangement/intramolecular Friedel-Crafts cyclization of propargyl acetates

An unprecedented Lewis acid-catalyzed cascade 1,3-rearrangement/Friedel-Crafts cyclization of propargyl acetates is developed for the construction of polycyclic bridged indene derivatives in moderate to good yields. This practical procedure features mild conditions, broad substrate scope, and easy operation.

TMSOTf mediated ‘5/6-endo-dig’ reductive hydroamination for the stereoselective synthesis of pyrrolidine and piperidine derivatives

A TMSOTf mediated 5/6-endo-dig reductive hydroamination cascade on internal alkynylamines gave expedient, stereoselective access to pyrrolidine and piperidine derivatives. We also demonstrate that a protecting group on nitrogen has a profound effect on the reactivity as well as diastereoselectivity.