Selective oxidation of zirconocyclopentenes via organoboranes.
[reaction: see text] A new, convenient, one-pot protocol is described for oxidation of zirconocyclopent-2-enes selectively at the sp(3) carbon by efficient transfer to electrophilic ((c)Hex)(2)BCl followed by oxidation with H(2)O(2)/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.
Gorman
Jeffrey S T
JS
Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712, USA.
Iacono
Scott T
ST
Pagenkopf
Brian L
BL