Cobalt-Catalyzed Regioselective Olefin Isomerization Under Kinetic Control

Olefin isomerization
is a significant transformation in organic
synthesis, which provides a convenient synthetic route for internal
olefins and remote functionalization processes. The selectivity of
an olefin isomerization process is often thermodynamically controlled.
Thus, to achieve selectivity under kinetic control is very challenging.
Herein, we report a novel cobalt-catalyzed regioselective olefin isomerization
reaction. By taking the advantage of fine-tunable NNP-pincer ligand
structures, this catalytic system features high kinetic control of
regioselectivity. This mild catalytic system enables the isomerization
of 1,1-disubstituted olefins bearing a wide range of functional groups
in excellent yields and regioselectivity. The synthetic utility of
this transformation was highlighted by the highly selective preparation
of a key intermediate for the total synthesis of minfiensine. Moreover,
a new strategy was developed to realize the selective monoisomerization
of 1-alkenes to 2-alkenes dictated by installing substituents on the
γ-position of the double bonds. Mechanistic studies supported
that the in situ generated Co–H species underwent migratory
insertion of double bond/β-H elimination sequence to afford
the isomerization product. The less hindered olefin products were
always preferred in this cobalt-catalyzed olefin isomerization due
to an effective ligand control of the regioselectivity for the β-H
elimination step.