Polymer-Supported Synthesis of Pyridines via [2+2+2] Cycloaddition

Significance

The highly chemoselective crossed [2+2+2] cycloaddition of polymer-supported alkyne 1, alkynes 2, and nitriles 3 was demonstrated. The reaction was found to proceed in the precence of CpCo(CO)₂ in toluene at 80 °C to give polymer-supported pyridines. Although pyridine (from the incorporation of two alkynes 2 and nitrile 3) and benzene (from the incorporation of three alkynes 2) byproducts were generated, these byproducts could be removed by simple filtration. The resulting pyridine units were cleaved from PS-supports by treatment with TFA to give pyridinemethanols 5 in 43-85% overall yields.