Catalytic enantioselective synthesis of (20S)-camptothecin intermediates using cyanosilylation of ketones promoted by D-glucose-derived lanthanide catalyst

An efficient catalytic enantioselective synthetic route was developed for Curran's versatile camptothecin intermediate (5). The key step is the catalytic enantioselective cyanosilylation of ketone (7) using a chiral samarium (Sm) complex. The target ketone cyanohydrin (6) was obtained with 90% ee using 2 mol % of the catalyst. A gadolinium (Gd) complex derived from the same chiral ligand could also be used as an enantioselective catalyst to synthesize Corey's intermediate (11).