Origin of Stereocontrol in Guanidine-Bisurea Bifunctional Organocatalyst That Promotes α-Hydroxylation of Tetralone-Derived β-Ketoesters: Asymmetric Synthesis of β- and γ-Substituted Tetralone Derivatives via Organocatalytic Oxidative Kinetic Resolution

The mechanism of asymmetric a-hydroxylation of tetralone-derived beta-ketoesters with guanidine-bisurea bifunctional organocatalyst in the presence of cumene hydroperoxide (CHP) was examined by means of DFT calculations to understand the origin of the stereocontrol in the reaction. The identified transition-state model was utilized to design an enantioselective synthesis of beta- or gamma-substituted tetralones by catalytic oxidative kinetic resolution reaction of tetralone-derived beta-ketoesters. This kinetic resolution reaction proceeded with high selectivity, and selectivity factors (s value) of up to 99 were obtained. The potential utility of this oxidative kinetic resolution method for synthesis of natural products was confirmed by applying it to achieve an enantioselective synthesis of (+)-linoxepin (13) from beta-substituted tetralone rac-7 in only six steps.