Woodward reaction

A formal equivalent of Woodward reaction has been developed, which is based on the addition of hypervalent iodine species (Scheme 3).28... 

The proper choice of stoichiometric oxidant allows either syn-or anft -selective dihydroxylations. NaI04 as the oxidizing agent generates H20 as a side product of the oxidation and therefore enables the Woodward Reaction to take place. 

The Woodward Reaction (or Woodward c/s-Hydroxylation) 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 Prevost Reaction gives crn/z -diols. 

If, on the other hand, aqueous acetic acid is added to the reaction mixture containing the positively charged intermediate, the product is a monoester of the diol, which, on hydrolysis, gives a diol. Such a reaction mimics a syn addition (Woodward reaction) [781, 783]. 

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. 

Alkenes, Arenes, and Alkanes. The catalytic cis-dihydroxylation of alkenes with iron complexes and Oxone as terminal oxidant has been reported by Che and coworkers. A wide range of electron-rich, electron-poor, aliphatic, aromatic, terminal, and o , -unsaturated alkenes were tolerated under the optimized reaction conditions. For example, methyl cinnamate could be transformed into the diol 9 on a 30 mmol scale with traces of undesired products 10 and 11 being isolated as side products (eq 98). Oxone has also been employed in the diastere-oselective dihydroxylation of alkenes in a catalytic approach to the Prevost-Woodward reaction. Up to 77% yield was obtained in the dihydroxylation of styrene however, NaI04 was found to be a superior oxidant affording the diol in 87% yield (eq 99). 

An interesting example with a switchover of the stereochemical course was observed during the enantioselective diacetoxylation of alkenes using chiral iodine (III) reagents (Scheme 13) [56]. Enantioselective Prevost and Woodward reaction products were formed through the optically active l,3-dioxolan-2-yl cation intermediates 30. 

A recent example L. Emmanuvel, T.M. A. Shaikh, A. Sudalai, Nal04 / LiBr-mediated diastereoselective dihydroxylation of olefins a catalytic approach to the Prevost-Woodward reaction, Org. Lett. 7 (2005) 5071-5074. 

---