RHODIUM-CATALYZED [2+2+2] CYCLOADDITION FOR THE SYNTHESIS OF SUBSTITUTED PYRIDINES, PYRIDONES, AND THIOPYRANIMINES

The transition-metal-catalyzed [2+2+2] cycloaddition of alkynes with nitriles is a useful and atom-economical method for the synthesis of substituted pyridines. The use of isocyanates and isothiocyanates in place of nitriles affords substituted pyridones and thiopyranimines, respectively. This review comprehensively covers the [2+2+2] cycloaddition reactions catalyzed by rhodium complexes for the synthesis of substituted pyridines, pyridones, and thiopyranimines. Asymmetric variants of these rhodium-catalyzed [2+2+2] cycloaddition reactions are also described.