Dihydroxylation and Aminohydroxylation of Alkenes Os

When an alkene is treated with OSO4, an osmate ester containing two new C-O bonds is formed. The osmate ester is hydrolyzed, usually with aqueous NaHSC 3, to give a 1,2-diol. The overall dihydroxylation reaction is stereospecifically syn. 

0s04 can catalyze the dihydroxylation of alkenes in the presence of a stoichiometric oxidant and water. The catalytic reaction is valuable because OSO4 is very expensive and extremely toxic. The catalytic version also allows one to use the nonvolatile Os(VI) salt K20s02(0H)4 in place of the volatile Os(VIII) complex OSO4. 

Problem 6.7. Propose a mechanism by which the oxidation of OsC 2(OH)2 to 0s04 by R3NO may occur. Hint The 0s04 product contains the O atom derived from the amine oxide. 

Chiral amines and K20sC 2(0H)4 are also used to catalyze the Sharpless asymmetric aminohydroxylation. The stoichiometric oxidant in aminohydroxylation is a deprotonated /V-lialoamide, whose mechanistic behavior is very similar to NMO. The reaction proceeds by a mechanism essentially identical to that of Sharpless dihydroxylation. 

Problem 6.8. Draw a mechanism for the following Sharpless aminohydroxylation  

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