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有机人名反应:Woodward ReactionWoodward cis-Hydroxylation
2011-03-05 21:20:07 来源:不详 浏览:4512
Woodward Reaction
Woodward cis-Hydroxylation

The Woodward Reaction allows the synthesis of syn-diols from alkenes by the addition of iodine followed by nucleophilic displacement with acetate in the presence of water. Hydrolysis of the intermediate ester gives the desired diol.

The Prvost Reaction gives anti-diols.


Mechanism of the Woodward Reaction

Similar to thePrvost Reaction, initial addition of iodine leads to a cyclic iodonium ion, that is opened through nucleophilic substitution by acetate anion:

A cyclic acetoxonium ion is then formed:

In contrast to the course of the Prvost Reaction, water appears to add readily as a nucleophile to the partially positive carbon atom of the intermediate. The cyclic orthoacetate is then cleaved to a monoacylated diol:

The desired diol can be isolated after hydrolysis.

Woodward noted (J. Am. Chem. Soc. 1958, 80, 209-211), that his modification of the Prvost reaction offers the opposite facial selectivity as compared to oxidations with OsO4 in the hydroxylation of synthetic steroid intermediates. Here, the steric approach factors first direct the stereochemistry of the iodination, which is followed by hydroxylation from the opposite face, whereas OsO4 leads to the isomeric cis-diol by direct attack from the most accessible face.

In a recent modification described by Sudalai (see also thePrvost Reaction), NaIO4 acts both as the stoichiometric oxidant and as a source of water:

 

Recent Literature


NaIO4/LiBr-mediated Diastereoselective Dihydroxylation of Olefins: A Catalytic Approach to the Prevost-Woodward Reaction
L. Emmanuvel, T. M. A. Shaikh, A. Sudalai, Org. Lett., 2005, 7, 5071-5074.


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