Stereochemical inversion in the vinylic substitution of boronic esters to give iodonium salts: participation of the internal oxy group.
[reaction: see text] Alkenylboronic esters having an acyloxy, alkoxy, or methoxycarbonyl group were employed for the reaction with (diacetoxyiodo)benzene in the presence of BF(3).OEt(2) to provide the alkenyliodonium tetrafluoroborates with inversion of configuration: (E)- and (Z)-boronates give (Z)- and (E)-iodonium salts, respectively. This selectivity can be reversed by the addition of ether to the dichloromethane solution. The stereoselectivity can be explained by participation of the neighboring oxy group.
Graduate School of Material Science, Himeji Institute of Technology, University of Hyogo, Kohto, Kamigori, Hyogo 678-1297, Japan. fuji@sci.u-hyogo.ac.jp
Morifumi
M
Fujita
Hee Jin
HJ
Lee
Tadashi
T
Okuyama