(2-Fluoroallyl)boration of Ketones with (2-Fluoroallyl)boronates

Efficient routes toward activation
of gem-chlorofluorocyclopropane-derived
(2-fluoroallyl)­boronates for allylboration of various ketones including
functionalized and low-reactive ones were developed. Increasing the
boron electrophilicity by the transformation of a boronate moiety
into a borinic ester with nBuLi/trifluoroacetic
anhydride (TFAA) makes (2-fluoroallyl)­boration of acetyl arenes/hetarenes
and aliphatic ketones possible with high diastereoselectivity. For
low-reactive or sterically hindered ketones (e.g., benzophenone, adamantanone),
“CuF”-based catalysts were developed: (NHC)­CuF·HF
and (NHC)­CuOTf in the presence of an excess of KHF2 (NHC
= IPr, SIPr, IPrCl).