Selective Oxidation of Zirconocyclopentenes via Organoboranes

A new, convenient, one-pot protocol is described for oxidation of zirconocyclopent-2-enes selectively at the sp3 carbon by efficient transfer
to electrophilic (cHex)2BCl followed by oxidation with H2O2/NaOH to afford 1-alkylidene-2-hydroxymethylcyclopentanes. Results with several
substrates show that overall reaction efficiencies for the zirconocene-mediated enyne cyclization, boron transmetalation, and oxidation sequence
are generally comparable to yields obtained from protonation of intermediate zirconocycles. The formation of E/Z olefin isomers from the
cyclization-oxidation sequence and an acid-catalyzed pinacol-type rearrangement of a vinylsilane are described.