Induction of Planar Chirality Using Asymmetric Click Chemistry by a Novel Desymmetrisation of 1,3-Bisalkynyl Ferrocenes

Abstract

The new asymmetric click CuAAC reaction is used for the first time to induce asymmetry in planar chiral compounds. There are only three classes of stereogenicity (atom-centred, axial and planar), and these results are therefore of fundamental importance as well as practical significance, providing access to chiral ferrocenes at near enantiopurity. Here, we report asymmetric induction (AI) and kinetic resolution (KR) studies on a novel library of prochiral 1,2,3-trisubstituted bis-alkynylferrocenes, obtained by diiodination, derivatisation (including reduction and etherification), double Sonogashira coupling and finally transesterification, azidation or silylation. Desymmetrisation using chiral ligands to modify the CuAAC reaction proceeds in up to 60 % yield and >99.5 % ee, yielding planar chiral ferrocenes. The absolute configuration of two of the preferred products was proved by chemical correlation and related to the entire series by circular dichroism spectroscopy (CD).