Oxy-Allyl Cation Catalysis: An Enantioselective Electrophilic Activation Mode

A generic
activation mode for asymmetric LUMO-lowering catalysis
has been developed using the long-established principles of oxy-allyl
cation chemistry. Here, the enantioselective conversion of racemic
α-tosyloxy ketones to optically enriched α-indolic carbonyls
has been accomplished using a new amino alcohol catalyst in the presence
of electron-rich indole nucleophiles. Kinetic studies reveal that
the rate-determining step in this SN1 pathway is the catalyst-mediated
α-tosyloxy ketone deprotonation step to form an enantiodiscriminant
oxy-allyl cation prior to the stereodefining nucleophilic addition
event.