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1.9.7 Dihydroxylation of Alkenes (I2/RCO2Ag)
Under anhydrous conditions a solution of iodine in CCl4 and equiv molar amount of silver acetate or silver benzoate transform alkenes into the diacetyl/dibenzoyl derivatives of the trans glycol, which on hydrolysis give trans diols. This reaction is known Prevost dihydroxylation of alkenes. In contrast, if the reaction is free from anhydrous conditions (in presence of water), cis diacetate or dibenzoate is obtained, which on saponification gives cis diols. This is called Woodward dihydroxylation of alkenes (Scheme 2-3).
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Scheme 4 |
Proposed Mechanism
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Scheme 3 |