Hypervalent iodine-mediated fragmentation of tertiary cyclopropanol systems

The reaction of tertiary cyclopropanol systems with hypervalent iodines in a protic solvent caused oxidative bond cleavage at C-1-C-2 and C-2-C-3 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 beta-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.