A practical and enantioselective organocatalytic alkylation with benzodithiolylium tetrafluoroborate

The alpha-alkylation of aldehydes is an important transformation. It was and in some way it is still considered the " Holy Grail" of organocatalysis. 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 tetrafluoborate 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.