Synthesis of Cyclopentadienols by Rhodium-Catalyzed C–H Activation of 8‑Formylquinolines and [2+2+1] Carbocyclization with Alkynes

An efficient Rh­(III)-catalyzed redox-neutral [2+2+1] coupling between 8-formylquinolines and alkynes has been realized for the synthesis of cyclopentadienols with broad substrate scope and functional group tolerance. The reaction occurs via C (acyl)–H activation with double insertion of the alkyne in high atom-economy. Instead of simply undergoing a [2+2+1] cyclization, a subsequent formal intermolecular 1,5-shift of the hydroxyl group is involved, which affords a thermodynamically more stable, conjugated cyclopentadienol

Synthesis of Cyclopentadienols by Rhodium-Catalyzed C–H Activation of 8‑Formylquinolines and [2+2+1] Carbocyclization with Alkynes

An efficient Rh­(III)-catalyzed redox-neutral [2+2+1] coupling between 8-formylquinolines and alkynes has been realized for the synthesis of cyclopentadienols with broad substrate scope and functional group tolerance. The reaction occurs via C (acyl)–H activation with double insertion of the alkyne in high atom-economy. Instead of simply undergoing a [2+2+1] cyclization, a subsequent formal intermolecular 1,5-shift of the hydroxyl group is involved, which affords a thermodynamically more stable, conjugated cyclopentadienol

Access to Quaternary Stereogenic Centers via Rhodium(III)-Catalyzed Annulations between 2‑Phenylindoles and Ketenes

Rh­(III)-catalyzed C–H activation of arenes and mild oxidative [4 + 2] annulative coupling with ketenes have been realized. The uniquely high reactivity of the C(3) of 2-phenylindoles was successfully utilized to facilitate the reductive elimination process, leading to efficient synthesis of cyclic products with a quaternary carbon stereocenter

Base-Promoted N‑Pyridylation of Heteroarenes Using <i>N</i>‑Propargyl Enaminones as Equivalents of Pyridine Scaffolds

N-Pyridylation of various N-heteroarenes, including N-heteroarene-containing peptides, was achieved using <i>N</i>-propargyl enaminones (isolated or generated in situ from propargyl amine and propynones) as masked polysubstituted pyridine cores. This metal-free procedure proceeds under mild reaction conditions and generates 1 equiv of H₂O as the sole byproduct

Base-Promoted N‑Pyridylation of Heteroarenes Using <i>N</i>‑Propargyl Enaminones as Equivalents of Pyridine Scaffolds

N-Pyridylation of various N-heteroarenes, including N-heteroarene-containing peptides, was achieved using <i>N</i>-propargyl enaminones (isolated or generated in situ from propargyl amine and propynones) as masked polysubstituted pyridine cores. This metal-free procedure proceeds under mild reaction conditions and generates 1 equiv of H₂O as the sole byproduct

Rh(III)- and Zn(II)-Catalyzed Synthesis of Quinazoline <i>N</i>‑Oxides via C–H Amidation–Cyclization of Oximes

Quinazoline <i>N</i>-oxides have been prepared from simple ketoximes and 1,4,2-dioxazol-5-ones via Rh­(III)-catalyzed C–H activation–amidation of the ketoximes and subsequent Zn­(II)-catalyzed cyclization. The substrate scope and functional group compatibility were examined. The reaction features relay catalysis by Rh­(III) and Zn­(II)

Cooperative Co(III)/Cu(II)-Catalyzed C–N/N–N Coupling of Imidates with Anthranils: Access to 1<i>H</i>‑Indazoles via C–H Activation

Cooperative cobalt- and copper-catalyzed C–H activation of imidate esters and oxidative coupling with anthranils allowed efficient synthesis of 1<i>H</i>-indazoles in the absence of metal oxidants. The anthranil acts as a convenient aminating reagent as well as an organic oxidant in this transformation. The copper catalyst likely functions at the stage of N–N formation

Redox-Neutral Access to Isoquinolinones via Rhodium(III)-Catalyzed Annulations of <i>O</i>‑Pivaloyl Oximes with Ketenes

A mild and redox-neutral [4 + 2] annulation of O-pivaloyl oximes with ketenes has been realized for synthesis of quaternary-carbon-stereocenter-containing (QCSC) isoquinolinones, where the N-OPiv not only acts as an oxidizing group but also offers coordination saturation to inhibit protonolysis. The reaction mechanism has been studied by DFT calculations

Rhodium-Catalyzed Oxidative Synthesis of Quinoline-Fused Sydnones via 2‑fold C–H Bond Activation

Rh­(III)-catalyzed synthesis of mesoionic heterocycles has been achieved via C–H activation of sydnones and oxidative coupling with internal alkynes. This reaction occurred under mild conditions with high efficiency, broad substrate scope, and low catalyst loading. Moreover, synthetic applications of a coupled product have been demonstrated in the late-stage derivatization into a variety of highly functionalized scaffolds