Cobalt-Mediated, Enantioselective Synthesis of C-2 and C-1 Dienes

The asymmetric C-H functionalization of norbornene and norbornadiene with five-, six-, and seven-membered cyclicenones mediated by the reactive intermediate [{eta(5)-((BuMe2Si)-Bu-1)C5H4}Co(NO)(2)] is reported. A novel base mixture derived from enantiopure ammonium salts and NaHMDS was used as a source of chirality, and this enantioselective desymmetrization of C-s alkenes has been applied to the asymmetric synthesis of G(2)- and C-1-symmetric diene ligands in high regioselectivity (3.7-20:1 anti/syn), near perfect diastereoselectivity (>99:1 dr), and high enantioselectivity (90-96% ee).