Gold-catalyzed domino cycloisomerization/Pictet-Spengler reaction of 2-(4-aminobut-1-yn-1-yl)anilines with aldehydes: synthesis of tetrahydropyrido[4,3-b]indole scaffolds

Gold Self-Relay Catalysis Enabling Regioselective Bicyclization toward [5]Azahelicenes

A gold self-relay catalysis driving a double annulation cascade starting from soft electron-biased 1,2-di(o-aminoaryl)alkynes and aldehydes is reported, enabling regioselective access to produce a series of [5]azahelicenes depending on the substitution pattern in generally good yields under mild conditions. This protocol exploits and unifies the π- and σ-Lewis acid capability of gold catalysts, featuring high molecular convergence, broad substrate flexibility, and good functional group compatibility and regioselectivity.

Synthesis of Nitrogen-Containing Heterocyclic Scaffolds through Sequential Reactions of Aminoalkynes with Carbonyls

Sequential reactions of aminoalkynes represent a powerful tool to easily assembly biologically important polyfunctionalized nitrogen heterocyclic scaffolds. Metal catalysis often plays a key role in terms of selectivity, efficiency, atom economy, and green chemistry of these sequential approaches. This review examines the existing literature on the applications of reactions of aminoalkynes with carbonyls, which are emerging for their synthetic potential. Aspects concerning the features of the starting reagents, the catalytic systems, alternative reaction conditions, pathways and possible intermediates are provided.

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.

Synthesis of 1-indolyl-3,5,8-substituted γ-carbolines: one-pot solvent-free protocol and biological evaluation

1,5-Disubstituted indole-2-carboxaldehyde derivatives 1a-h and glycine alkyl esters 2a-c are shown to undergo a novel cascade imination-heterocylization in the presence of the organic base DIPEA to provide 1-indolyl-3,5,8-substituted γ-carbolines 3aa-ea in good yields. The γ-carbolines are fluorescent and exhibit anticancer activities against cervical, lung, breast, skin, and kidney cancer cells.

Au(I)-Catalyzed Pictet-Spengler Reactions All around the Indole Ring

Au(I) complexes catalyze iso-Pictet-Spengler reactions. Ethylamine or methylamine chains were introduced at C2, C4, or the nitrogen atom of the indole ring, and the corresponding substrates were reacted in the presence of aldehydes and catalytic amounts of Au(I) complexes, leading to a variety of polycyclic scaffolds. Selectivity could be achieved in the course of a double iso-Pictet-Spengler reaction involving two successive aldehydes, leading to highly complex molecules.

The Pictet-Spengler Reaction Updates Its Habits

The Pictet-Spengler reaction (P-S) is one of the most direct, efficient, and variable synthetic method for the construction of privileged pharmacophores such as tetrahydro-isoquinolines (THIQs), tetrahydro-β-carbolines (THBCs), and polyheterocyclic frameworks. In the lustro (five-year period) following its centenary birthday, the P-S reaction did not exit the stage but it came up again on limelight with new features. This review focuses on the interesting results achieved in this period (2011-2015), analyzing the versatility of this reaction. Classic P-S was reported in the total synthesis of complex alkaloids, in combination with chiral catalysts as well as for the generation of libraries of compounds in medicinal chemistry. The P-S has been used also in tandem reactions, with the sequences including ring closing metathesis, isomerization, Michael addition, and Gold- or Brønsted acid-catalyzed N-acyliminium cyclization. Moreover, the combination of P-S reaction with Ugi multicomponent reaction has been exploited for the construction of highly complex polycyclic architectures in few steps and high yields. The P-S reaction has also been successfully employed in solid-phase synthesis, affording products with different structures, including peptidomimetics, synthetic heterocycles, and natural compounds. Finally, the enzymatic version of P-S has been reported for biosynthesis, biotransformations, and bioconjugations.

Catalytic C3 aza-alkylation of indoles

The aza-alkylation reaction at position 3 of the indole scaffold allows the introduction of a differently substituted aminomethyl group, with the formation of a stereogenic centre. Critical summary of 2000–2019 meaningful papers.

Recent advances in the synthesis of indoles from alkynes and nitrogen sources

This review highlights ten years of success in the synthesis of indoles using alkynes and nitrogen sources as substrates.

Gold-catalyzed enantioselective functionalization of indoles

This review documents the potential of enantioselective gold catalysis for the functionalization of indoles.

Silver(i)-catalyzed sequential hydroamination and Prins type cyclization for the synthesis of fused benzo-δ-sultams

An intramolecular annulation strategy has been developed for the synthesis of tetrahydrobenzo[e]pyrano[4,3-c][1,2]thiazine derivatives by means of coupling of aldehydes with 2-(4-hydroxybut-1-yn-1-yl)-N-arylsulfonamides using a catalytic amount of silver hexafluoroantimonate in toluene at 80 °C. This is the first report on the synthesis of fused benzo-δ-sultam derivatives through C-N, C-O, and C-C bond formations. The reaction proceeds through a cascade of hydroamination and Prins type cyclization.

Tandem cyclization of o-alkynylanilines with isocyanides triggered by intramolecular nucleopalladation: access to heterocyclic fused 2-aminoquinolines

Herein, a novel strategy for the synthesis of various heterocyclic fused 2-aminoquinolines via palladium-catalyzed tandem cyclization of o-alkynylanilines with isocyanides has been developed. This process includes trans-oxy/aminopalladation, isocyanide insertion, elimination and 1,3-hydrogen migration. Besides high atom and step economy, this method shows good functional group compatibility with excellent chemo- and regioselectivities under mild reaction conditions.

Electronically modified amine substituted alkynols for regio-selective synthesis of dihydrofuran derivatives

An efficient approach has been developed for the regio-selective synthesis of iodo-dihydrofurans from amino alkynols. These dihydrofurans have been further diversified by C–C, C–N coupling reactions.

Cooperative Multicatalytic System for the One-Pot Synthesis of Octahydrospiro-β-carbolines

A domino cyclization of 3-((3-(2-aminophenyl)prop-2-ynylamino)methyl)but-3-en-1-ol with aldehydes has been accomplished employing 5 mol % of the Ph3PAuCl/AgSbF6/In(OTf)3 system to afford the corresponding octahydrospiro[pyran-4,4'-pyrido[3,4-b]indole] derivatives in good yields with high selectivity. This is the first report on the synthesis of spiro-β-carbolines through a multicatalytic cascade process.

An expedient approach to pyrrolo[3,2-c]quinolines via regioselective formation of the pyrrole nucleus over indoles

The regioselective synthesis of pyrrolo[3,2-c]quinolines from protected 2-alkynylanilines by Heck and intramolecular Michael addition has been described.