Radical chemistry of 1,4-alkadiynes has been scarcely studied due to the lack of selective methods for radical generation, a susceptibility of propargyl radicals to acetylene-allene rearrangement and a low regioselectivity at the carbon-carbon bond formation step. The complexation of the triple bond with a dicobalthexacarbonyl cluster allows for stabilization of the alpha-alkynyl propargyl cation and regioselective radical dimerization occurring selectively alpha to a metal core. The scope of the reaction yielding symmetrical and unsymmetrical 1,1,2,2-tetraynes was expanded by varying the nature and bulkiness of substituents at select acetylenic termini. The diastereoselectivity was found to be dependent upon the bulkiness of the gamma substituent with a TMS-group providing the highest level of diastereocontrol (d,l>99%). Introduction of a double bond into tetraynes provided access to 1,1,2,2-tetrayne ethylenes, a class of polyconjugated molecules of immediate relevance to dendrimer and medicinal chemistries.

Radical reactions of 1,4-alkadiynes: Regio-, chemo-, and stereoselective C-C bond formation mediated by a metal core

248th National Meeting (2014)

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