Prévost reaction

The Prévost reaction is chemical reaction in which an alkene is converted by iodine and the silver salt of benzoic acid to a vicinal diol with anti stereochemistry. [cite journal
author = Charles Prévost
journal = Comptes rendus
volume = 196
pages = 1129
year = 1933
title = Sur un complexe iodo-argento-benzoïque et son application à l'oxydation des combinaisons éthyléniques en α-glycols
url = http://gallica.bnf.fr/ark:/12148/bpt6k3148d/f1129.table ] [Charles Prévost; C.A. 27, 3195 (1933)] [Wilson, C. V. "Org. React." 1950, "9", 350. (Review) ] THe reaction was discovered by the French chemist Charles Prévost (1899-1983).

Reaction mechanism

The reaction between silver benzoate (1) and iodine is very fast and produces a very reactive iodinium benzoate intermediate (2). The reaction of the iodinium salt (2) with an alkene gives another short-lived iodinium salt (3). Nucleophilic substitution (S_N2) by the benzoate salt gives the ester (4). Another silver ion causes the neighboring group substitution of the benzoate ester to gives the oxonium salt (5). A second S_N2 substitution by the benzoate anion give the desired diester (6).

In the final step hydrolysis of the ester groups gives the anti-diol. This outcome is the opposite of that of the related Woodward cis-hydroxylation which gives syn addition.

References

ee also

*Woodward cis-hydroxylation