Asymmetric dihydroxylation of 2-substituted 1-vinylferrocenes:: The first non-enzymatic kinetic resolution of planar-chiral ferrocenes

The first non-enzymatic kinetic resolution of planar chiral ferrocenes has been achieved by the Sharpless catalytic asymmetric dihydroxylation (AD) of a set of racemic 2-substituted 1-ethenylferrocenes 1a-d. The enantioselectivity factor k(rel) varies from 20 to 62 [for (DHQD)(2)PYR ligands], and from 5 to 27 [for (DHQ)(2)PYR ligands]. The stereochemical outcome of the resolution can be easily predicted by the mnemonic device for AD, with the additional hypothesis that in the preferred transition state the olefin group and the upper cyclopentadiene ring of vinylferrocenes exhibit an essentially coplanar geometry.