Provost reaction

Provost reaction. This reaction constitutes an important step in a synthesis of frans-7,8-dihydroxy-anfi-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (3), considered to be the ultimate carcinogenic metabolite of benzo[a]pyrene. To obtain satisfactory yields, the silver benzoate should be freshly prepared (method of Newman and Beal, 1, 1004), and the biphase reaction should be stirred efficiently (Vibromixer with a large stirring blade). ... 

The first step of the Provost reaction is the reaction of the alkene with iodine to form the cyclic iodonium ion. Next, the iodonium ion is stereospecifically opened by the silver carboxylate to form the corresponding frans-1,2-iodo carboxylate. The iodine is displaced intramolecularly by the carbonyl group of the carboxylate (anchimeric assistance) to form a cyclic cationic intermediate. In the absence of water, this cation is opened with the inversion of configuration by the second equivalent of silver carboxylate to afford the frans-1,2-dicarboxylate. However, in the presence of water Woodward-Brutcher modification) the common intermediate is converted to a c/s-orthocarboxylate which is hydrolyzed to the corresponding c/s-1,2-diol. 

Ogata reports iodination of aromatic compounds in fair yield by reaction with iodine and peracetic acid in acetic acid solution the effective reagent may be acetyl hypoiodite, CH3COOI. The reagent reacts with cyclohexene to give l-iodo-2-acetoxycyclohexane, but in low yield." The Provost reaction Is far better. 

A possible, alternative synthesis would be the reaction of one mole of a conduritol tetrabenzoate with one mole of silver benzoate and an excess of iodine (the Provost reaction ). 

One of the most useful modifications of the Woodward dihydroxylation was published by Cambie and Rutledge.12 This modification employs TIOAc in place of AgOAc and describes complementary procedures for the synthesis of cw-diols (Woodward reaction) and frans-diols (Provost reaction).13 Thus, treatment of cyclohexene 13 with TIOAc and I2 in HOAc at 80 °C, followed by the addition of water, affords acetate 14. Hydrolysis of 14 then gives cw-diol 15 in 70-75% yield. On the other hand, exposure of cyclohexene 13 to TIOAc, I2, and HOAc at reflux in the absence of water affords bis-acetate 16, which upon hydrolysis gives /raw-diol 17. 

Replacement of hydrogen by acoxy groups A novel Provost reaction... 

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