Oxidative cyclizations diacetoxyiodo benzene

Oxidation of a nitroamine with (diacetoxyiodo)benzene (review [3714]) often gives better results in this cyclization than are obtained with hypochlorite. 

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]. 

The methodology, based on generation of the alkoxy radicals, has also been used for the oxidative cyclization of various alcohols. For example, the irradiation of alcohols 588 with (diacetoxyiodo)benzene and iodine affords the chroman derivatives 589 in moderate to good yields (Scheme 3.232) [631]. 

An efficient catalytic method for sulfonyloxylactonization of alkenoic acids using (diacetoxyiodo)benzene as a recyclable catalyst in combination with m-chloroperoxybenzoic acid as an oxidant in the presence of a sulfonic acid has been reported [38]. This reaction effects the cyclization of alkenoic acids 28 in dichloromethane at room temperature, giving tosyloxylactones 29 in good yields (Scheme 4.12). 

A similar catalytic phosphoryloxylactonization of pentenoic acids has been reported. In particular, the cyclization of 4-pentenoic acids 30 with phosphates using (diacetoxyiodo)benzene as a catalyst in combination with mCPBA as the terminal oxidant in CF3CH2OH at room temperature affords phosphoryioxylactones 31 in good yields (Scheme 4.13) [39]. 

Methyl ester of serine rac-1 under treatment with (diacetoxyiodo) benzene (BAIB) and iodine gives radical 2, which is oxidized to give acyliminium ion 3. This intermediate is then trapped with acetate to yield N,0-acetal 4. The acyliminium ion 3 can regenerate from the acetal and react with vinyl arenes to produce the intermediate 5. In the final step, an intramolecular cyclization furnishes the 6-aryl-5,6-dihydro-4H-l,3-oxazine 6, with the ds isomer rac-6a as the major product (Scheme 5.3) [8]. In a similar domino process, aminosugars provide substituted oxazines, which are analogs of C-nudeosides [8]. 

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