Cyclizations diacetoxyiodo benzene

Numerous different mechanistic approaches have been applied for this combination. First, cyclization of phenoxy-ethanols 203, in the presence of (diacetoxyiodo)benzene and iodine, gave a mixture of 1,4-benzodioxane 13 and 6-iodo-l,4-benzodioxane 204 via alkoxy radicals (Equation 36) <1997J(P 1)787, 1996TL2441>. 

AT-Substituted amidines 74 are transformed via the carbodiimide intermediate 75 into urea derivatives 76 as shown in Scheme 34 [141]. This reaction has been performed with a variety of aliphatic and aromatic substituents and in addition to (diacetoxyiodo)benzene 3 other hypervalent iodine compounds can also be used for this rearrangement. Phenyl substituted amidines 74 (R = Ph) can lead to cyclized products of type 77. 

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]. 

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

Hypervalent iodine(III) compounds, such as [bis(trifluoroacetoxy)iodo]benzene, (diacetoxyiodo)benzene and [hydroxy(tosyloxy)iodo]benzene, are commonly used as reagents in various cationic cyclizations, rearrangements and fragmentations. Numerous examples of such reactions have been reported in the literature and summarized in the reviews dedicated to synthetic applications of hypervalent iodine compounds [4,7,10,11, 180, 191, 387]. 

Moriarty and coworkers have developed a convenient synthetic approach to 2-benzimidazolones, 2-benzoxazolones and related compounds based on the Hofmann-type rearrangement in the reaction of anthranilamides, salicylamides and some P-substituted amides with (diacetoxyiodo)benzene [501]. For example, various 2-benzimidazolones (401, X = NR) and 2-benzoxazolones (401, X = O) were prepared by the treatment of amides 400 with (diacetoxyiodo)benzene in a basic methanolic solution (Scheme 3.160). This reaction probably occurs via initial Hofmann-type rearrangement followed by intramolecular cyclization of the intermediate isocyanate [501]. 

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]. 

Useful synthetic methodologies are based on the cyclization or rearrangement of the nitrogen-centered radicals generated in the reaction of the appropriate amides with (diacetoxyiodo)benzene in the presence of iodine [652-655]. Specific examples are illustrated by the synthesis of bicyclic spirolactams 622 from amides 621 [653] and preparation of the oxa-azabicyclic systems (e.g., 624) by the intramolecular hydrogen atom transfer reaction promoted by carbamoyl and phosphoramidyl radicals generated from the appropriately substituted carbohydrates 623 (Scheme 3.244) [654],... 

Togo, Yokoyama and coworkers have developed a useful synthetic procedure for the preparation of nitrogen heterocycles based on the N-radical cyclization onto an aromatic ring [247, 656-658], For example, various iV-alkylsaccharins 626 can be conveniently prepared in moderate to good yields by the reaction of arenesul-fonamides 625 with (diacetoxyiodo)benzene in the presence of iodine under irradiation with a tungsten lamp (Scheme 3.245) [656]. A similar procedure has been applied to the synthesis of 1,2,3,4-tetrahydroquinoline derivatives [247, 657] and 3,4-dihydro-2,l-benzothiazine 2,2-dioxides [658],... 

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]. 

Togo and Moroda have reported a (diacetoxyiodo)benzene-mediated cyclization reaction of 2-aryl-A-methoxyethanesulfonamides 49 using iodobenzene as apre-catalyst (5-10 mol%) and m-chloroperoxybenzoic... 

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]. 

An interaction of the intermediate carbon-centered radical (A) with a neighboring carbon-carbon bond in this ring expansion leads to a transannular radical cyclization the treatment of the unsaturated decanols with (diacetoxyiodo) benzene-iodine followed by irradiation underwent fragmentation of intermediate allyloxy radicals (A) to give the bicyclo(5.3.0]decanones (40-78%) and to give the 7,5,5-tricycKc compound (81%) by way of a Billiard reaction, as outlined in Scheme 687 ... 

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