Transition metal-catalyzed [2+2] cycloadditions between bicyclic alkenes and
alkynes provides an efficient method for the construction of cyclobutene rings. Various
transition metal complexes, including those of cobalt, nickel, ruthenium, rhodium, and
rhenium, have been used to catalyze [2+2] cycloadditions between bicyclic alkenes and
alkynes. The purpose of this review is to summarize and discuss the various aspects of
transition metal-catalyzed [2+2] cycloaddition between bicyclic alkenes and alkynes,
including the development of metal catalysts, the mechanisms of the cycloadditions
catalyzed by different metal catalysts, the reactivity of the alkene and the alkyne
components in the cycloaddition, the compatibility of different functional groups on the
alkene and the alkyne components, the chemo- and regioselectivity of the cycloadditions
between unsymmetrical substrates, and the asymmetric induction studies using chiral
auxilliaries on the alkyne component in addition to the use of using chiral ligands. The
scope and limitations of each catalyst in the [2+2] cycloadditions will also be discussed.
Keywords: Transition metal, cycloaddition, bicyclic alkene, alkyne, cyclobutene,
bicyclic alkene, cycloaddition, alkyne, propargylic alcohol, cyclobutene,
norbornadiene, norbornene, benzonorbornadiene, oxanorbornadiene, regioselectivty,
transition metal, catalysis, ruthenium, nickel, cobalt, palladium, rhodium, rhenium,
iridium, mitsudo reaction.
