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.