超原子価ヨウ素試薬によるシクロプロパノール系の開裂反応とその応用

抄録

The reaction of tertiary cyclopropanol systems with hypervalent iodines in a protic solvent caused oxidative bond cleavage at C₁-C₂ and C₂-C₃ leading to alkenoic acids or their corresponding esters in high yields. In the cases of the compounds bearing an alkyl group on the cyclopropane-ring, the endo-compound gave only the (Z) -alkene while the exo-compound afforded only the (E) -alkene. A strong acid catalyst promoted these reactions. In fluorinated alcohols, the oxidation of cyclopropanol systems with phenyliodine (III) diacetate caused a mixture of enones and β-acetoxyketones. On the other hand, phenyliodine (III) bistrifluoroacetate afforded alkenoic esters. The asymmetric synthesis of (-) -pinidine and its enantiomer was achieved by starting from norgranatanone via the asymmetric enolization, stereoselective cyclopropanation, and ring cleavage of the resulting cyclopropanol system with a hypervalent iodine as key steps. Formal asymmetric synthesis of (+) -indolizidine 223 AB was also accomplished.