Boron-Catalyzed, Diastereo- and Enantioselective Allylation of Ketones with Allenes

The diastereo- and enantioselective allylation of ketones
remains
a synthetic challenge, with transition metal catalysis offering the
most applied methods. Here, a boron-catalyzed allylation of ketones
with allenes is presented. Excellent yield, regioselectivity, and
diastereoselectivity were found across functionalized substrates.
The reaction was further developed to accommodate an enantioenriched
boron catalyst and thus gave asymmetric ketone allylation in good
yield, diastereoselectivity, and enantioselectivity. Mechanistic studies
supported a hydroboration–allylation–transborylation
pathway.