Inter- and Intramolecular Cobalt (I)-Catalyzed [2+2+2] Cyclizations of Bisnitriles
Audet, Megan Ann
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The cobalt (I)-catalyzed intramolecular [2+2+2] cyclization reactions previously investigated by Vollhardt were successfully applied to alkynylbisnitrile species in the formation of novel annulated pyridazines. This chemistry demonstrates the first successful formation of an N,N- bond through a [2+2+2] cyclization pathway. Nitrogen linkers with different protecting groups were incorporated into the alkynylbisnitrile species, and were used as a site of selective deprotection and diversification of the cyclized scaffold. Using this methodology, two novel ureas were formed from the annulated pyridazines with high yields (88-93%), indicating the feasibility of the development of a diverse small molecule library using this chemistry. Expanding upon the success in the intramolecular cyclizations, the intermolecular incorporation of alkynes and nitriles with arylbisnitriles was examined. Although the intermolecular incorporation of diphenylacetylene was found to only provide trace amounts of the desired product, favoring the trimerization product, benzonitrile was found to incorporate well, forming the corresponding 1,2,4-triazine regioselectively (44%).
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