Rhodium(III)‐catalyzed Cleavage of C−C Bond and C−H Bond Cascaded by Michael Addition for the Conversion of α‐Hydroxy Ketones to Phthalides and Isocoumarins

Abstract A protocol for Rh(III)‐catalyzed cleavage of C−C bond and C−H bond cascaded by Michael addition of α ‐hydroxy ketones was established. The method allows the rapid construction of phthalides and isocoumarins skeleton. A total of 62 phthalides and isocoumarins were obtained with yields up to 91% demonstrating the broad applicability of the protocol. This efficient cascade catalysis can be applied to the total synthesis of the natural products isoochracinic acid and sparstolonin B. The reaction mechanism, especially the dimerization process of the α‐hydroxyketone, is unique. Further studies of the reaction using control experiments, in situ NMR analysis, cyclic voltammogram and isotope tracking experiments have provided insight into the reaction mechanism.