Asymmetric Carbonium Ion Catalysis: The Intramolecular Hydroalkoxylation of Cyclopropanes.

Cyclopropanes serve as valuable synthetic intermediates in drug discovery and natural product synthesis. However, the stereoselective functionalization of cyclopropanes remains a fundamental challenge, traditionally necessitating the prior activation of the parent hydrocarbon. Here, we report an organocatalytic asymmetric intramolecular hydroalkoxylation of cyclopropanes that overcomes this constraint using chiral imidodiphosphorimidate catalysts. Our strategy directly affords enantioenriched substituted tetrahydrofurans with high enantioselectivity (up to 96.5:3.5 er). Kinetic analyses reveal a zero-order dependence on the substrate and support catalyst saturation. Combined experimental and computational studies suggest that the prereaction catalyst-substrate ion pair is stabilized through noncovalent interactions leading to the formation of a transient cycloproponium ion-like transition state. This work provides a potentially general platform for stereoselective cyclopropane functionalization.