Gold(I)-Catalyzed Reactions between N-(o-Alkynylphenyl)imines and Vinyldiazo Ketones to Form 3-(Furan-2-ylmethyl)-1H-indoles via Postulated Azallyl Gold and Allylic Cation Intermediates

Rh(iii)-catalyzed sp3/sp2-C-H heteroarylations via cascade C-H activation and cyclization

The development of an efficient strategy for facile access to quinoline-based bis-heterocycles holds paramount importance in medicinal chemistry. Herein, we describe a unified approach for accessing 8-(indol-3-yl)methyl-quinolines by integrating Cp*Rh(iii)-catalyzed C(sp3)-H bond activation of 8-methylquinolines followed by nucleophilic cyclization with o-ethynylaniline derivatives. Remarkably, methoxybiaryl ynones under similar catalytic conditions delivered quinoline tethered spiro[5.5]enone scaffolds via a dearomative 6-endo-dig C-cyclization. Moreover, leveraging this method for C8(sp2)-H bond activation of quinoline-N-oxide furnished biologically relevant oxindolyl-quinolines. This reaction proceeds via C(sp2)-H bond activation, regioselective alkyne insertion, oxygen-atom-transfer (OAT) and intramolecular nucleophilic cyclization in a cascade manner. One C-C, one C-N and one C[double bond, length as m-dash]O bond were created with concomitant formation of a quaternary center.

Advancements in Gold-Catalyzed Cascade Reactions to Access Carbocycles and Heterocycles: An Overview

This review summarizes recent developments (from 2006 to 2022) in numerous important and efficient carbo- and heterocycle generations using gold-catalyzed cascade protocols. Herein, methodologies involve selectivity, cost-effectiveness, and ease of product formation being controlled by the ligand as well as the counter anion, catalyst, substrate, and reaction conditions. Gold-catalyzed cascade reactions covered different strategies through the compilation of various approaches such as cyclization, hydroarylation, intermolecular and intramolecular cascade reactions, etc. This entitled reaction is also useful for the synthesis of spiro, fused, bridged carbo- and heterocycles.

Photoinduced ynamide structural reshuffling and functionalization

The radical chemistry of ynamides has recently drawn the attention of synthetic organic chemists to the construction of various N-heterocyclic compounds. Nevertheless, the ynamide-radical chemistry remains a long-standing challenge for chemists due to its high reactivity, undesirable byproducts, severe inherent regio- and chemoselective problems. Importantly, the ynamide C(sp)-N bond fission remains an unsolved challenge. In this paper, we observe Photoinduced radical trigger regio- and chemoselective ynamide bond fission, structural reshuffling and functionalization of 2-alkynyl-ynamides to prepare synthetically inaccessible/challenging chalcogen-substituted indole derivatives with excellent step/atom economy. The key breakthroughs of this work includes, ynamide bond cleavage, divergent radical precursors, broad scope, easy to handle, larger-scale reactions, generation of multiple bonds (N-C(sp²), C(sp²)-C(sp²), C(sp²)-SO₂R/C-SR, and C-I/C-Se/C-H) in a few minutes without photocatalysts, metals, oxidants, additives. Control experiments and ¹³C-labeling experiments supporting the conclusion that sulfone radicals contribute to ynamide structural reshuffling processes via a radical pathway.

Although ynamides have emerged as a versatile class of compounds for organic synthesis, the radical chemistry of ynamides usually proceeds with the expected connectivity largely intact. Here the authors show a methodology by which the C(sp)–N bond undergoes scission, alkyne migration and functionalization under blue LED light in the absence of metals or additives.

Synthesis of C7-Functionalized Indoles through an Aromaticity Destruction-Reconstruction Process

A process for the synthesis of C7-functionalized indoles using para-substituted 2-alkynylanilines as starting materials was reported. The process involves a dearomatization, an 1,2-addition by organic lithium or Grignard reagents, an aromatization-driven allylic rearrangement, and a cyclization. A variety of groups including alkyl, aryl, alkenyl, or alkynyl groups were selectively installed at the C7 site of indoles leading to the formation of 2,5,7-trisubstituted indoles.

Selective oxidation of alcohol-d 1 to aldehyde-d 1 using MnO2

The selective oxidation of alcohol-d₁ to prepare aldehyde-d₁ was newly developed by means of NaBD₄ reduction/activated MnO₂ oxidation. Various aldehyde-d₁ derivatives including aromatic and unsaturated aldehyde-d₁ can be prepared with a high deuterium incorporation ratio (up to 98% D). Halogens (chloride, bromide, and iodide), alkene, alkyne, ester, nitro, and cyano groups in the substrates are tolerated under the mild conditions.

A facile method for deutrium incorporation into aldehydes by mild reduction of NaBD₄ of aldehydes and MnO₂ oxidation (98% D) is disclosed.

Gold-Catalyzed Tandem Oxidative Coupling Reaction between β-Ketoallenes and Electron-Rich Arenes to 2-Furylmethylarenes

A tandem oxidative coupling reaction of β-ketoallenes and arenes was developed, which leads to the formation of 2-furylmethylarenes using AuCl₃ and phenyliodine diacetate. The Au^III salt catalyzed the cyclization of β-ketoallenes to form a 2-furylmethyl gold intermediate, and the subsequent C-H functionalization of arenes proceeded smoothly. During the oxidative coupling, nucleophilic additions occurred at the center and terminal carbon atoms of the allene moiety to form C-O and C-C bonds.

Gold-Catalyzed Synthesis of Diaza-hexatrienes Via Diazo Attack at Vinylgold Carbenes: An Easy Access to 1H-Pyrazolo[4,3-b]pyridine-5-ones

This work reports a gold-catalyzed stereoselective synthesis of highly substituted E-configured 2,3-diaza-1,3,5-hexatrienes using α-diazo nitriles and cyclopropene derivatives; such products arise from an atypical diazo attack of α-aryldiazo nitriles at vinylgold carbenes. For these 2,3-diaza-1,3,5-hexatrienes, we develop a novel anionic cyclization of derivatives of one family to form 1H-pyrazolo[4,3-b]pyridine-5-ones.

Asymmetric Synthesis of 3-Methyleneindolines via Rhodium(I)-Catalyzed Alkynylative Cyclization of N-(o-Alkynylaryl)imines

The first asymmetric synthesis of 3-methyleneindolines from alkynyl imines has been developed via a rhodium-catalyzed tandem process: regioselective alkynylation of the internal alkynes and subsequent intramolecular addition to the imines. The reaction proceeded with unconventional chemoselectivity and provided 3-methyleneindolines with good yields (up to 82% yield) and high enantioselectivities (up to 97% ee). Moreover, this transformation also features mild reaction conditions, perfect atom economy, and a broad substrate scope.