Syntheses of Hypervalent Allenyliodinanes and Iodo-Claisen Rearrangement

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Recently, we reported that the reaction of propargylsilanes with aryliodinanes in the presence of BF3-Et2O undergoes a reductive iodonio-Claisen rearrangement under mild conditions, yielding ortho-propargyl iodoarenes in good yields. The reductive ortho-propargylation probably involves the intermediate formation of allenyl(aryl)iodinanes, which undergo [3,3]-sigmatropic rearrangement. The lack of the crossover products argues for the intramolecularity of the rearrangement. With (p-methoxy)aryliodinanes, an ipso iodonio-Claisen rearrangement is observed. To detect the intervention of the allenyl(aryl)iodinanes in the reductive propargylations of aryliodinanes, we have carried out the reaction of 1-hydroxy-1,2-benziodoxol-3(1H)-one with 1,3-bis-(trimethylsilyl)-3-methylbut-1-yne. The reaction, however, led to the unexpected formation of an (alkylperoxy)iodinane.Alkylperoxyiodinanes have never been synthesized probably because of their high tendency to decompose. When 1-hydroxy-1,2-benziodoxol-3(1H)-one was treated with tert-butyl hydroperoxide in the presence of BF_3-Et_2O in chloroform at room temperature, the alkylperoxyiodinane, 1-tert-butylperoxy-1,2-benziodoxol-3(1H)-one was obtained as colorless plates in 85% yield. The peroxyiodinane was fully characterized by spectral data and the structure was unambiguously established by a single-crystal X-ray analysis. We found that the peroxyiodinane is a versatile oxidizing reagent in organic synthesis, and can oxidize sulfides to sulfoxides or sulfones, selenides to selenoxides, phosphines to phosphine oxides, and olefins to epoxides. Deprotection of dithioacetals to ketones as well as oxidation at benzylic positions yielding carbonyl compounds were also achieved. Furthermore, the peroxyiodinane was found to be an efficient reagent for oxidation of amines to imines.