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Synthesis of Fused Pyridines via Solid-Supported Cyclotrimerization Reaction
D. D. Young, A. Deiters*
North Carolina State University, Raleigh, USA
23 August 2007 (online)
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.