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 acetoxybenziodaz ole 3 with TMSN3, TsOH . H2O, MsOH, or TMSOTf, respectively. Reaction of triflate 10 with alcohols (methanol, ethanol, 2-propanol, and 2-ada mantanol) 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 establ ished by a single-crystal X-ray analysis. The results of ab initio mol ecular orbital calculations on structures 3 and 11 are in good agreeme nt with X-ray structural data. The calculation results indicate that t he driving force of the novel rearrangement of benziodazoles to 3-imin iumbenziodoxoles is the greater thermodynamic stability of the N-proto nated 3-iminobenziodoxoles relative to O-protonated benziodazol-3-ones by about 9.0 (MP2: 10.8) kcal/mol in the case of the acetoxy substitu ted 3 and 3d compounds and 15 kcal/mol (MP2: 13.5 kcal/mol) for the me thoxy-substituted derivatives 11 and 13.