Theoretical study on the origin of enantioselectivity in the bis(dihydroquinidine)-3,6-pyridazine center dot osmium tetroxide-catalyzed dihydroxylation of styrene

The origin of enantioselectivity in the dihydroxylation of H2C=CH(Ph) catal yzed by (DHQD)(2)PYDZ . OsO4 ((DHQD)(2)PYDZ = bis(dihydroquinidine)-3,6-pyr idazine) is analyzed theoretically by means of hybrid QM/MM calculations wi th the IMOMM(Becke3LYP:MM3) method. Twelve different possible reaction path s are defined from the three possible regions of entry of the substrate and its four possible orientations and characterized through their respective transition states. The transition state with the lowest energy leads to the R product, in agreement with experimental results. The decomposition of th e interaction energy between catalyst and substrate shows how the selectivi ty is essentially governed by stacking interactions between aromatic rings, with a leading role for the face-to-face interaction between the substrate and one of the quinoline rings of the catalyst.