A practical and enantioselective organocatalytic alkylation with benzodithiolylium tetrafluoroborate

摘要

The a-alkyiation of aldehydes is an important transformation. It was and in some way it is still considered the "Holy Grail" of organocataiysis. However, it is still not possible to introduce methyl groups by using methyl iodide as electrophile in a stereoselective organocatalytic promoted alkylation of aldehydes or ketones. The stabilization of carbenium ion by sulfur allowed us to introduce a quite straightforward methodology for a formal a-methylation of aldehydes. The commercially available benzodithiolylium fefrafluoborate is a stable carbenium ion with a rich chemistry and interesting properties. Furthermore, it can be easily removed by nickel Raney or it can be oxidized to the corresponding carbonyl group.