Propargyl radical chemistry: renaissance instigated by metal coordination

Accounts of Chemical Research
Gagik G Melikyan

Abstract

Over the last two decades, radical chemistry of propargyl systems was developed into a potent synthetic field providing access to classes of organic compounds that are otherwise hardly accessible. The levels of diastereoselection thus achieved (up to 100%) are unprecedented for free propargyl radicals, as well as for organic radicals π-bonded to transition metals. These advances were enabled by the coordination of the triple bond to a Co2(CO)6 core that precluded an acetylene-allene rearrangement, stabilized requisite propargyl cations, created conformational constraints at the carbon-carbon bond formation site, configurationally altered the acetylenic moiety allowing for 1,3-steric induction upon the newly formed stereocenters, increased bulkiness of propargyl triads thus controlling the spatial orientation of converging radicals, and allowed for α-to-γ projection of the reaction site and alteration of the transiency of radical intermediates. In the course of these studies, a number of popular "beliefs" were proven to be untrue. First, cobalt-complexed propargyl cations, which have long been considered to be thermally labile species, were engaged in synthetically meaningful transformation at temperatures as high as 147 °C. Sec...Continue Reading

References

Oct 17, 2009·The Journal of Organic Chemistry·Gagik G MelikyanEdwin Abedi

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