A Versatile Approach to the Solution-Phase Combinatorial Synthesis of Substituted Pyridines:  The Cobalt-Catalyzed Cyclotrimerization of Alkynes with a Nitrile

The cobalt-catalyzed trimerization of two alkynes and one nitrile was exploited to produce solution-phase libraries of pyridines. Upon addition of 2 equiv of a CO scavenger (i.e., an amine-N-oxide), the commercially available [CpCo(CO)2] proved to be an attractive catalyst, as the required reaction temperatures, side product formation (i.e., carbocycles), and oxygen sensitivity are moderate. Purification of the reaction mixture was performed with an acidic cation-exchange resin.