Os-catalyzed asymmetric dihydroxylation Sharpless reaction

Os-catalyzed dihydroxylation of alkenes was probably one of the first density fimctional theory (DFT)-based investigations of a metal-catalyzed asymmetric reaction (Norrby, Sharpless). The latest available computational work devoted to the stereocontrol of this reaction was 

When 3D structure of SI is qualitatively analyzed, however, only one face-to-face interaction with only one quinoline ring (which is conjugated with the second, quinoline A) can be found. Although the C-H proton is indeed orientated toward pyridazine s N=N bond, the bond length of this C-H proton is not elongated (-1.10 A), whereas the distances between C atom and H atom with the center of N=N bond is 3.85 and 2.76 A, respectively, rather suggesting that this interaction is not significantly important. 

Note that based on earlier experimental studies from Sharpless group, it was concluded that some n-n stacking may bring important consequences for tile reaction enantioselectivity when unsaturated substrates are used. For example, whereas dihydroxylation of styrene afforded the product witii 97% ee and vinylcyclohexane afforded the product with 84% ee. The value 84% for nonsaturated substrate can be explained in terms of weak C(sp )-H... ji hydrogen-bonding interactions between a substrate and a catalyst. Similar C(sp )-H...n hydrogen-bonding interactions between the 

For the so-called Sharpless mnemonic and electronic polarizability-based stereochemical models, both qualitative 2D prediction tools for the absolute configuration in this reaction, an interested reader is addressed to the corresponding original publications. 

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