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Nativi, C.; Roelens, S., Science of Synthesis, (2008) 36, 759.
A development of the catalytic asymmetric dihydroxylation (AD) of alkenes is ligand heterogenization (on silica gel,[13–15] or soluble[16,17] or insoluble [18,19] polymeric supports), followed by osmium complexation. This method allows the recovery and reuse of the expensive and toxic osmium catalyst. An alternative ion-exchange technique can also be used; the catalyst is immobilized on layered double hydroxides (LDH) through the exchange of the osmium(VIII) oxide dianion (Scheme 3).[20] The exchanger–osmium(VIII) oxide catalyst is successfully employed for the asymmetric dihydroxylation of several alkenes 4, to afford syn-diols 5, with higher yields and comparable enantiomeric excesses to those obtained using the corresponding homogeneous conditions. Various co-oxidants, such as 4-methylmorpholine N-oxide, potassium hexacyanoferrate(III), and molecular oxygen, can be used for the asymmetric dihydroxylation reaction under heterogeneous conditions. Among the heterogeneous osmium catalysts, the osmium(VIII) oxide dianion exchanged onto layered double hydroxides[21] displays excellent activity with 4-methylmorpholine N-oxide as the co-oxidant; however, it has been reported that the use of potassium hexacyanoferrate(III) and molecular oxygen deactivate LDH–osmium(VIII) oxide over a number of recycling steps.[20] The resin–osmium(VIII) oxide reagent shows good performance in terms of catalyst recovery and reusability, irrespective of the co-oxidant employed.
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References
[13] | Meee, M. M.; Meee, M. M.; Me, M.-M., Meeeeeeeeee: Meeeeeeee, (8888) 8, 888. |
[14] | Meee, M.; Meeeeeee, M.; Meeeeee, M., Meee. Meeeee. (Meeeeeeee), (8888), 8888. |
[15] | Meeeeeee, M.; Meeeeee, M. M., Mee. Meee., (8888) 8, 8888. |
[16] | Meee, M.; Meeeeee, M., Meeee. Meee., (8888) 888, 888; Meeee. Meee. Mee. Me. Meee., (8888) 88, 888. |
[17] | Mee, M.; Meeee, M. M., Meeee. Meee., (8888) 888, 8888; Meeee. Meee. Mee. Me. Meee., (8888) 88, 8888. |
[18] | Mee, M. M.; Meeeeeeee, M. M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[19] | Meee, M.; Meeee, M.; Meeee, M.; Meeeee, M.; Meeeeeeee, M., Meeeeeeeeee Meee., (8888) 88, 8888. |
[20] | Meeeeeee, M. M.; Meeeeeee, M. M.; Meeeee, M.; Meeeee, M. M., M. Me. Meee. Mee., (8888) 888, 8888. |
[21] | Meeeee, M., Meeee Meee Meeee., (8888) 88, 888. |
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