Ruthenium(II)-Catalyzed Oxidative Double C–H Activation and Annulation Reaction: Synthesis of Indolo[2,1-a]isoquinolines

Ru(II)-catalyzed oxidative coupling of sulfoxonium ylides with amines: efficient synthesis of α-ketoamides and indolo[2,1-a]isoquinolines

The first use of sulfoxonium ylides for the synthesis of α-ketoamides is described via a Ru(II)-catalyzed amidation reaction with amines. The same Ru(II)-catalyzed reaction of sulfoxonium ylides with 2-phenylindoles provided indolo[2,1-a]isoquinolines instead of α-ketoamides.

Palladium-Catalyzed Carbonylative Synthesis of Amide-Containing Indolo[2,1-a]isoquinolines from Alkene-Tethered Indoles and Nitroarenes

In this new procedure, amide-containing indolo[2,1-a]isoquinoline scaffolds were prepared by palladium-catalyzed carbonylative cyclization of alkene-tethered indoles with nitroarenes. By using Mo(CO)₆ as the CO source and reductant and nitroarenes as the nitrogen source, this reaction produced various amide-containing indolo[2,1-a]isoquinoline derivatives in good yields in general. Furthermore, the late-stage modifications of bioactive molecules using this protocol were demonstrated as well.

Rh(III)-Catalyzed Oxidative Domino C-H/N-H Annulation: Diarylureas as Arylamine Donors for the Assembly of Indolo[2,1-a]isoquinolines

An efficient and convenient Rh(III)-catalyzed double aryl C(sp2)-H bond and N-H activation and annulation reaction is reported for the synthesis of indolo[2,1-a]isoquinolines in the presence of the Cu(OAc)₂ oxidant under heating conditions. Distinct from previous works with other arylamine donors, one molecule of 1,3-diarylurea can serve as a precursor of two molecules of arylamine in the reaction with diaryl-substituted alkynes.

Three-component synthesis of arylsulfonyl-substituted indolo[2,1-a]isoquinolinones and benzimidazo-[2,1-a]isoquinolin-6(5H)-ones by SO2 insertion and radical cascade cyclization

An efficient arylsulfonylation/cyclization of 2-aryl-N-methacryloyl indoles with potassium metabisulfite and aryldiazonium tetrafluoroborates was developed. A series of variously substituted arylsulfonyl indolo[2,1-a]isoquinolin-6(5H)-ones were formed in moderate to good yields via utilization of the nature abundant inorganic salt potassium metabisulfite as a SO₂ surrogate. Additionally, this three-component protocol can also be employed for the synthesis of arylsulfonyl-substituted benzimidazo-[2,1-a]isoquinolin-6(5H)-ones.

Multiple annulations of inert C(sp2)-H bonds with alkynes

Transition-metal catalyzed directing group (DG) assisted annulation of inert C-H bonds leads to the formation of complex molecular frameworks from readily accessible substrates. Thus, multiple annulation of less functionalized substrates with unsaturated species leads to the construction of structurally diverse fused poly(hetero)cycles. The directed inert C(arene)-H bond activation and the mode of TM-migration in this process could enabled obatining L-type [involves DG heteroatom, o-C(arene)-H bond, and C(arene)-H bond of aryl-motif in alkyne], Y-type [involves two heteroatoms of the DG and o-,o'-C(arene)-H bonds], and B-type [involves o-C(arene)-H bond and m-C(arene)-H bond] π-extended annulation products. The coordination preference of the DG heteroatom makes the transformation chemo- and regio-selective. This article underlines the conceptual development of unsymmetrical multiple annulation of arene C(sp²)-H bonds with alkynes, which is exceedingly appealing and highly important.

Cascade Cyclization for the Synthesis of Indolo[2,1-α]isoquinoline Derivatives via Visible-Light-Induced Halogen-Atom-Transfer (XAT) and Hydrogen-Atom-Transfer (HAT)

A transition metal-free photoredox cascade cyclization is herein reported. In this protocol, sustainable visible light was used as energy source and organic light-emitting molecule Eosin Y served as efficient photocatalyst....

Pd(ii)-Catalyzed regioselective functionalization of antipyrines: synthesis of pyrazolono-maleimides and pyrazolono-quinones

A Pd(ii)-catalyzed direct functionalization reaction of the 4Csp²-H bond of antipyrine derivatives is reported. This metal-catalyzed reaction of antipyrines with maleimides provided an easy and efficient access to biologically important pyrazolonomaleimides. This catalytic system is also applicable for C-4 functionalization of the antipyrine ring with quinone derivatives.

Electrochemical synthesis of versatile ammonium oxides under metal catalyst-, exogenous-oxidant-, and exogenous-electrolyte-free conditions

An electrochemical oxidative cross-coupling reaction between 2.5-substituted-pyrazolin-5-ones and ammonium thiocyanate has been developed, which resulted in a series of unprecedented cross-coupling products under metal catalyst-, exogenous-oxidant-, and exogenous-electrolyte-free conditions. It is worth noting that since the resulting cross-coupling products are nearly insoluble in MeCN, the pure product could be afforded without silica gel column purification. In addition, the prepared ammonium oxides are versatile building blocks for synthesizing functionalized pyrazole derivatives.

Recent advances in the synthesis of pyrido[1,2-a]indoles

This review deals with the different accesses leading to the pyrido[1,2-a]indole nucleus in the last 20 years.

Ruthenium-Catalyzed C–H Activations for the Synthesis of Indole Derivatives

The synthesis of substituted indoles has received great attention in the field of organic synthesis methodology. C–H activation makes it possible to obtain a variety of designed indole derivatives in mild conditions. Ruthenium catalyst, as one of the most significant transition-metal catalysts, has been contributing in the synthesis of indole scaffolds through C–H activation and C–H activation on indoles. Herein, we attempt to present an overview about the construction strategies of indole scaffold and site-specific modifications for indole scaffold via ruthenium-catalyzed C–H activations in recent years.

Transition metal-catalyzed coupling of heterocyclic alkenes via C–H functionalization: recent trends and applications

Heterocyclic alkenes and their derivatives are an important class of reactive feedstock and valuable synthons. This review highlights the transition-metal-catalyzed coupling of heterocyclic alkenes via a C–H functionalization strategy.

Palladium-catalyzed domino Heck-disilylation and -borylation of alkene-tethered 2-(2-halophenyl)-1H-indoles: access to diverse disilylated and borylated indolo[2,1-a]isoquinolines

A chemoselective domino Heck-disilylation and -borylation reaction for generating various disilylated and borylated tetracyclic indolo[2,1-a]isoquinolines has been developed.

Rhodium-Catalyzed Successive C-H Bond Functionalizations To Synthesize Complex Indenols Bearing a Benzofuran Unit

An efficient rhodium-catalyzed redox-neutral annulations of N-phenoxyacetamides and ynones via successive double C-H bond activations has been developed. A series of novel and complex indenols bearing a benzofuran unit were generated with moderate to excellent regioselecetivities under mild conditions. Adding N-ethylcyclohexanamine (CyNHEt) could restrict the formation of the mono C-H bond activation byproduct, which is not the intermediate of the reaction demonstrated via the mechanistic investigations.