Microwave-Enhanced Rhodium-Catalyzed [2+2+2] Cycloaddition Reactions To Afford Highly Functionalized Pyridines and Bipyridines

Rhodium(I)-catalyzed [2+2+2] cycloaddition reactions of N-tosyl-, carbon-, and oxygen-tethered cyanodiynes in a completely intramolecular fashion have been optimized to afford highly functionalized pyridines by conventional and/or microwave heating. Microwaves have been shown to enhance the process by allowing the reaction to be conducted effectively in short reaction times. The methodology has been extended for the synthesis of bipyridines, either by treating a cyanodiyne with an appended pyridine or by conducting a double [2+2+2] cycloaddition reaction on a dicyanotetrayne scaffold. The choice of the solvent in the microwave heating reaction has been shown to be crucial for the success of the process.