Photocatalyzed [2 + 2 + 2]-Cycloaddition of Nitriles with Acetylene:  An Effective Method for the Synthesis of 2-Pyridines under Mild Conditions

Abstract

The photocatalyzed [2 + 2 + 2]-cycloaddition of nitriles with 2 equiv of acetylene to 2-pyridines can be carried out under mild conditions and represents a valuable extension to common synthetical methods. For the ideal wavelength range (350-500 nm), lamps as well as sunlight can be used. Working at room temperature and in organic solvents such as toluene or hexane as well as in water gives satisfying results in many cases. However, it is also possible to vary the solvent and the reaction temperature of the photocatalyzed synthesis and to choose, with respect to the specific substrate, specific requirements for this particular reaction and general requirements of the method. This simple and selective method derives its potential mainly from the large variety of applicable nitriles. Suitable substrates include (functionalized) aliphatic and aromatic nitriles as well as cyanamides derived from secondary amines.

The broad diversity of CpCo(I) complexes

“…An acetyl-substituted Cp ligand led to a faster conversion than an unsubstituted Cp ligand, while the indenyl ligand proved to have the slowest conversion rate, which is in accordance to the reports by Bönnemann and colleagues (Bönnemann et al 1984, Heller et al 2002.…”

Catalyzed Reactions of Alkynes in Water

“…It has been shown that the reaction was chemospecific and several different functional groups were well incorporated in this transformation without being protected, such as alcohols, ketones, and amines. [154] Additionally, photocatalyzed [2 + 2 + 2] alkyne or alkyne-nitrile cyclotrimerization in water [155][156][157] and cyclotrimerization in supercritical H 2 O [158,159] have been reported in recent years.…”

A Serendipitous Discovery: Nickel Catalyst for the Cycloaddition of Diynes with Unactivated Nitriles

“…[19] These cycloadditions possessed an expanded substrate scope as terminal diynes were successfully converted into pyridine products. [19] These cycloadditions possessed an expanded substrate scope as terminal diynes were successfully converted into pyridine products.…”