Mechanism of Osmium-Catalyzed Dihydroxylations

Recent theoretical investigations clearly favor the [3 + 2] mechanism [27, 62], The calculation of the respective transition states using DFT methods show significantly lower activation barriers for the [3 + 2] addition compared with the [2 + 2] reaction path. Subsequently, these results were also supported by the theoretical and experimental determination of the kinetic isotope effect of the AD reaction [28]. 

Of particular mechanistic interest in AD is the question of how chirality is transmitted from the chiral alkaloid ligand to the Os glycolate complex [33]. 

The enormous synthetic utility of AD depends on the one hand on the broad applicability of the osmium-catalyzed dihydroxylation for nearly every class of olefins, and on the other hand on the high selectivities which can be reached with optimized catalyst-ligand systems. 

Snyder, Ito, Corey, Fuji, Tomioka, Hanessian, Hirama et al. 

X-ray analysis of osmium tetroxide-cinchona alkaloid complexes [37] demonstrated that the chiral center in the alkaloid ligand is quite remote from the 0x0 ligand. Therefore it is unlikely that the complex itself is responsible for the 

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Scheme 2. General mechanism of osmium-catalyzed dihydroxylation.

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