Mechanism
The catalytically active species in the reaction most likely is an imidotrioxo osmium(VIII) complexes, which is formed in situ from the osmium reagent and the stoichiometric nitrogen source, i.e. chloroamine (Scheme 14). Experiments under stoichiometric conditions have been shown that imidotrioxo osmium(VIII) complexes transfer the nitrogen atom and one of the oxygen atoms into the substrate. The major regioisomer normally has the nitrogen placed distal to the most electron withdrawing group of the substrate.
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Scheme 14 |
1.1.5 Asymmetric Aminohydroxylation
The asymmetric cis-1,2-aminohydroxylation of alkenes with chloroamine has been explored using the chiral osmium catalyst derived from OsO4 and cinchona alkaloids, dihydroquinidine ligands (DHQD)2-PHAL and dihydroquinine ligands (DHQ)2-PHAL.
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The face selectivity for the aminohydroxylation can too be reliably predicted (Scheme 15).
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Scheme 15 |