Cobalt(II)-Catalyzed Stereoselective Olefin Isomerization: Facile Access to Acyclic Trisubstituted Alkenes

Stereoselective synthesis of trisubstituted
alkenes is a long-standing
challenge in organic chemistry, due to the small energy differences
between E and Z isomers of trisubstituted
alkenes (compared with 1,2-disubstituted alkenes). Transition metal-catalyzed
isomerization of 1,1-disubstituted alkenes can serve as an alternative
approach to trisubstituted alkenes, but it remains underdeveloped
owing to issues relating to reaction efficiency and stereoselectivity.
Here we show that a novel cobalt catalyst can overcome these challenges
to provide an efficient and stereoselective access to a broad range
of trisubstituted alkenes. This protocol is compatible with both mono-
and dienes and exhibits a good functional group tolerance and scalability.
Moreover, it has proven to be a useful tool to construct organic luminophores
and a deuterated trisubstituted alkene. A preliminary study of the
mechanism suggests that a cobalt-hydride pathway is involved in the
reaction. The high stereoselectivity of the reaction is attributed
to both a π–π stacking effect and the steric hindrance
between substrate and catalyst.