Synthesis and Properties of the Valence Tautomer of cis-Iodosocyclopropanecarboxylic Acid: 4,5-Methano-1-hydroxyiodoxol-3(1H)-one

Article abstract of DOI:10.1021/ja00199a036

4,5-Methano-1-hydroxyiodoxol-3(1H)-one (4) was synthesized from propionic acid in six steps.Key reactions included Simmons-Smith cyclopropanation of cis-3-iodopropen-2-ol, followed by pyridinium dichromate oxidation to cis-iodocyclopropanecarboxylic acid.The final iodo to iodoso oxidation used either chlorination/hydrolysis or peracetic acid procedures.Compound 4 exists in the 1-hydroxyiodoxolone form, not in the "open" cis-cyclopropanecarboxylic acid form (3), as shown by its "high" pK_a (7.55) and by its ability to cleave p-(nitrophenyl)diphenyl phosphate(k = 0.0044 s^-1) in pH 8 aqueous micellar solution.Compound 4 disproportionates to iodo (5) and iodoxy (7) compounds in pH 8 aqueous buffer with k = 0.027 L/(M*s).Ab initio molecular orbital calculations are described which help rationalize the observed properties of 4.The reactivity of 4 (and related species) is intimately connected to the structure and bonding around the formally hypervalent iodine atom.