Enantioselective Iron-Catalyzed Cross-[4+4]-Cycloaddition of 1,3-Dienes Provides Chiral Cyclooctadienes

Chiral cyclooctadienes are a frequently
occurring scaffold in natural
products and specialty chemicals, and are used as ligands in asymmetric
catalysis. Accessing substituted cyclooctadienes in an efficient asymmetric
fashion has been notoriously challenging. We report an iron-catalyzed
enantioselective cross-[4+4]-cycloaddition of 1,3-dienes to form substituted
cyclooctadienes under very mild conditions. A highly tailored chiral
α-diimine iron complex is key for the success of the transformation
providing a balanced performance between reactivity, excellent cross-selectivity
and very high enantioselectivity. Steric maps of the complexes help
accounting for the observed selectivity. The developed method allows
rapid and atom-economic access to novel differently functionalized
cyclooctadienes in very high yields and enantioselectivities.