A novel method for the generation of alpha-alkoxy propargyl radicals was developed, using the respective carbocations as precursors. It utilizes propargyl acetals as substrates, cobaltocene as a one-electron reducing agent, and a dicobalthexacarbonyl group as a stabilizing and stereodirecting auxiliary moiety. An experimental protocol includes a low-temperature treatment of propargyl acetals with triflic anhydride and the reduction of requisite propargyl triflates, leading to a radical C-C bond formation alpha to the metal core. The reaction design and a choice of reagents allowed for avoiding strong acids, such as tetrafluoroboric acid, and carrying out the reaction sequence under neutral conditions. The substrate base was expanded to include ketals and cyclic acetals, as well as intramolecular cyclizations of bis-propargyl acetals. The secondary transformations of alpha-alkoxy 1,5-alkadiynes and 1,5-cyclodecadiynes will be presented, along with an X-ray crystallographic analysis and oxidative decomplexation of radical dimers.

Propargyl acetals as new substrates in transition metal-mediated radical C-C bond formation reactions

243rd National Meeting (2012)

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