Structure and Chemistry of Hypervalent Iodine Heterocycles:  Acid-Catalyzed Rearrangement of Benziodazol-3-ones to 3-Iminiumbenziodoxoles

New 1-substituted benziodazoles, namely, azide 7, tosylate 8, mesylate 9, and triflate 10, were prepared by the reaction of acetoxybenziodazole 3 with TMSN 3, TsOH·H 2 O, MsOH, or TMSOTf, respectively. Reaction of triflate 10 with alcohols (methanol, ethanol, 2-propanol, and 2-adamantanol) afforded novel 1-alkoxy-3-iminiumbenziodoxoles 11a − d, while similar reactions with amides gave 1-amido-3-iminiumbenziodoxoles 12a − d in 51−89% yield. The structure of iminiumbenziodoxole 12b was established by a single-crystal X-ray analysis. The results of ab initio molecular orbital calculations on structures 3 and 11 are in good agreement with X-ray structural data. The calculation results indicate that the driving force of the novel rearrangement of benziodazoles to 3-iminiumbenziodoxoles is the greater thermodynamic stability of the N -protonated 3-iminobenziodoxoles relative to O -protonated benziodazol-3-ones by about 9.0 (MP2: 10.8) kcal/mol in the case of the acetoxy substituted 3 and 3d compounds and 15 kcal/mol (MP2: 13.5 kcal/mol) for the methoxy-substituted derivatives 11 and 13 .