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.