A Quick Access to 1-(2-Pyridyl)indolesviaSolvent-Free Ruthenium(II)-Catalyzed Chemo- and Regioselective [2+2+2] Cycloaddition of α,ω-Diynes andN-Cyanoindoles

Synthesis of 5H-chromeno[3,4-c]pyridine derivatives through ruthenium-catalyzed [2 + 2 + 2] cycloaddition

Efficient access to 5H-chromeno[3,4-c]pyridines using Ru-catalyzed [2 + 2 + 2] cycloaddition of α,ω-diynes with cyanamides was developed, providing valuable tricyclic pyridine building blocks and enabling access to a biologically relevant intermediate.

Synthesis of Benzo[c][2,7]naphthyridinones and Benzo[c][2,6]naphthyridinones via Ruthenium-Catalyzed [2+2+2] Cycloaddition between 1,7-Diynes and Cyanamides

A convenient method for the ruthenium-catalyzed synthesis of benzo[c]naphthyridinone derivatives is reported. The [2+2+2] cycloaddition from various mono- and disubstituted 1,7-diynes and cyanamides provided benzo[c][2,7]naphthyridinones as major products and benzo[c][2,6]naphthyridinones as minor ones in yields of ≤79% and regioselectivities of ≤99:1. This method is amenable to internal and terminal diynes and a number of cyanamides with diverse functional group tolerance.

Multicomponent syntheses of 5- and 6-membered aromatic heterocycles using group 4-8 transition metal catalysts

In this Perspective, we discuss recent syntheses of 5- and 6-membered aromatic heterocycles via multicomponent reactions (MCRs) that are catalyzed by group 4-8 transition metals. These MCRs can be categorized based on the substrate components used to generate the cyclized product, as well as on common mechanistic features between the catalyst systems. These particular groupings are intended to highlight mechanistic and strategic similarities between otherwise disparate transition metals and to encourage future work exploring related systems with otherwise-overlooked elements. Importantly, in many cases these early- to mid-transition metal catalysts have been shown to be as effective for heterocycle syntheses as the later (and more commonly implemented) group 9-11 metals.

Ruthenium-Catalyzed Cycloadditions to Form Five-, Six-, and Seven-Membered Rings

Ruthenium-catalyzed cycloadditions to form five-, six-, and seven-membered rings are summarized, including applications in natural product total synthesis. Content is organized by ring size and reaction type. Coverage is limited to processes that involve formation of at least one C-C bond. Processes that are stoichiometric in ruthenium or exploit ruthenium as a Lewis acid (without intervention of organometallic intermediates), ring formations that occur through dehydrogenative condensation-reduction, σ-bond activation-initiated annulations that do not result in net reduction of bond multiplicity, and photochemically promoted ruthenium-catalyzed cycloadditions are not covered.

Acid-catalyzed [2 + 2 + 2] cycloaddition of two cyanamides and one ynamide: highly regioselective synthesis of 2,4,6-triaminopyrimidines

Triflic acid (10 mol%) catalyzes the highly regioselective [2 + 2 + 2] cycloaddition between two cyanamides and one ynamide to grant the 2,4,6-triaminopyrimidine core. The developed synthetic method is effective for the preparation of a family of the diversely substituted heterocyclic products (30 examples; yields up to 94%). The synthesis can be easily scaled up and conducted in gram quantities. As demonstrated by the post-functionalizations involving the amino-substituents, the obtained heterocycles represent a useful platform for the construction of miscellaneous pyrimidine-based frameworks. The performed density functional theory calculations verified a particular role of H+, functioning as an electrophilic activator, in the regioselectivity of the cycloaddition.

Synthesis of Fluorescent Azafluorenones and Derivatives via a Ruthenium-Catalyzed [2 + 2 + 2] Cycloaddition

An original and mild synthetic route for the preparation of novel azafluorenones and derivatives via a ruthenium-mediated [2 + 2 + 2] cycloaddition of α,ω-diynes and cyanamides has been developed. This atom-economical catalytic process demonstrated remarkable regioselectivities to access fluorescent azafluorenone derivatives. The photophysical properties of azafluorenone derivatives have been evaluated, and photoluminescence phenomena at solid and liquid states have been highlighted.

Synthesis of 2-aminopyridines via ruthenium-catalyzed [2+2+2] cycloaddition of 1,6- and 1,7-diynes with cyanamides: scope and limitations

A direct route to access 2-aminopyridines using Ru-catalyzed-[2+2+2] cycloaddition of 1,n-diynes with cyanamides is described in excellent yields and regioselectivities.

Copper-Catalyzed Alkenylation of Cyanamides

An efficient procedure for the copper-catalyzed cross-coupling between a broad range of cyanamides and iodoalkenes is reported. Upon reaction with catalytic amounts of copper(I) iodide and 2,2'-bisimidazole in the presence of cesium carbonate in DMF at 80 °C, a fast, regioselective, and stereoretentive cross-coupling occurs. This reaction, which was found to have a broad substrate scope, provides the first general entry to N-alkenylcyanamides, building blocks that hold great synthetic potential.

Ruthenium-Catalyzed [2 + 2 + 2] Cycloaddition Reaction Forming 2-Aminopyridine Derivatives from α,ω-Diynes and Cyanamides

A novel, efficient, and mild synthetic route for the preparation of 2-aminopyridines via ruthenium-mediated [2 + 2 + 2] cycloaddition of α,ω-diynes and cyanamides has been developed. This atom-economical catalytic process demonstrated remarkable regioselectivities to access pyridine derivatives of high synthetic utility.

Solvent-free ruthenium trichloride-mediated [2 + 2 + 2] cycloaddition of α,ω-diynes and cyanamides: a convenient access to 2-aminopyridines

A convenient access to functionalized 2-aminopyridinesviaa solventless Ru-catalyzed [2 + 2 + 2] cycloaddition reaction of α,ω-diynes and cyanamides is described.

Silver(i) catalyzed intramolecular cyclization of N-(2-(alk-1-yn-1-yl))-1H-tetrazoles leading to the formation of N-cyano-2-substituted indoles under ambient conditions

Synthesis of N-heterocycles from N-(2-(alk-1-yn-1-yl))tetrazoles to obtain N-cyano 2-substituted indoles as selective products.

Synthesis of 3-(2-thiopyridyl)indoles via the ruthenium catalyzed [2 + 2 + 2] cycloaddition of diynes and 3-thiocyanatoindoles

A highly efficient protocol for the synthesis of 3-(2-thiopyridyl)indoles via the ruthenium(ii) catalyzed [2 + 2 + 2] cycloaddition reaction of α,ω-diynes with 3-thiocyanatoindoles under mild reaction conditions has been developed.