Synthesis of Fused Pyridines via Solid-Supported Cyclotrimerization Reaction

Significance

The well-known cobalt-catalyzed [2+2+2] cyclotrimerization has been developed as a polymer support reaction. Thus, trityl-protected dipropargylamine A tethered on a polystyrene resin was treated with excess benzonitrile and Co catalyst under microwave conditions to deliver the fused pyridines B in excellent yield and high purity after mild acidic cleavage from the resin. However, electron-poor nitriles failed to yield product and in a few systems, the same reaction in solution gave low yields of the fused pyridines. Generalization of the cyclo­trimerization to solid-supported diynes of type C and E is demonstrated to give the analogous oxygen ring-fused pyridines type D and F, respectively, in high yield with complete regio­selectivity. The cyclotrimerization of tethered alkynes G with isocyanates to pyridones was also studied.