Construction of aryliridium-salen complexes: enantio- and cis-selective cyclopropanation of conjugated and nonconjugated olefins

Two stable and optically active iridium-salen complexes were synthesized by introducing a tolyl or phenyl ligand at the apical position, respectively, via the S(E)Ar mechanism, and they were found to be efficient catalysts for cis-selective asymmetric cyclopropanation. The scope of the cyclopropanation was wide, and the reactions of not only conjugated mono-, di-, and trisubstituted olefins but also nonconjugated terminal olefins proceeded with high enantio- and cis-selectivity, even in the presence of a functional group such as an ether or ester. The utility of this cyclopropanation was demonstrated by a short step synthesis of 8-(1R,2S)-2-hexylcyclopropyl]octanoate, isolated from Escherichia coli B-ATCC 11303, using the reaction as the key step.