Lactones diacetoxyiodo benzene

Treatment of aryl-substituted alkenes with hypervalent iodine compounds can lead to the formation of phenyliodinated intermediates, which can be stabilized by the aryl substituent via the formation of phenonium ions. Subsequent nucleophilic attack might then lead to rearranged products. This behavior can be nicely seen by comparing the unsaturated carboxylic acids 78 in their reaction with (diacetoxyiodo)benzene 3. The substrate 78a without the phenyl substituent is cyclized to the phenyliodinated intermediate 79, which is then attacked by the acetate under the formation of lactone 81 [142]. Substrate 78b is, however, then stabilized by the formation of an intermediate phenonium ion 80 and attack by the acetate is accompanied by a 1,2-phenyl migration and 82 is generated, Scheme 35 [143]. 

As an alternative to the lead tetraacetate oxidation, (diacetoxyiodo)benzene can be used to initiate a fragmentation reaction which leads to unsaturated medium-sized lactones [110]. The structures of the starting materials are similar to those of compounds VII/157, VII/160, and VII/163. The same stereochemical consequences are observed as mentioned above. 

The (diacetoxyiodo)benzene-promoted oxidative iodolactonization of pentenoic acids 347 in the presence of tetrabutylammonium iodide proceeds smoothly at room temperature to afford lactones 348 in high yields (Scheme 3.138) [433]. A catalytic version of this iodolactonization using iodobenzene as a catalyst and sodium perborate monohydrate as the stoichiometric oxidant has also been reported (Section 4.1). 

Several useful synthetic methodologies are based on the generation of the oxygen-centered radicals from carboxylic acids and the (diacetoxyiodo)benzene-iodine system [613-617]. In particular, a direct conversion of 2-substituted benzoic acids 566 into lactones 567 via oxidative cyclization induced by [bis(acyloxy)iodo]arene/iodine has been reported (Scheme 3.224) [613,614]. 

Suarez et al. have reported a general method for the synthesis of alduronic acid lactones via fragmentation of carbohydrate anomeric alkoxy radicals [124] (Scheme 77). Treatment of hexopyranose derivative of the galacturonic acid, 342, with (diacetoxyiodo)benzene and iodine under mild conditions or with... 

For example, photolysis of steroidal hemiacetals with (diacetoxyiodo)benzene and iodine in the absence of oxygen affords medium-sized lactones as a result of alkoxy radical fragmentation (Equation 110.4). ... 

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