First-Principles\nCharacterization of Noncovalent Interactions\nin the Enantioselective Oxetane Ring Opening via SPHENOL-Based Chiral\nPhosphoric Acid Catalyst

The asymmetric ring-opening reaction of 3,3-substituted\noxetanes\ncatalyzed by chiral phosphoric acid (CPA) derived from a newly developed\nSPHENOL (2,2′,3,3′-tetrahydro-1,1′-spirobi[phenalene]-9,9′-diol)\nframework was investigated by performing density functional calculations.\nThe plausible transition states were traced by considering the oxetane\nactivation mode. The energy profiles obtained for various substrates\nprovide a rational understanding of the reaction at the atomic level.\nThe truncation models help to attribute the reaction initiation and\norigin of enantioselectivity to three types of noncovalent interactions\nbetween the catalyst and the substrate. The Quantum theory of atoms\nin molecules (QTAIM), Noncovalent Interactions (NCI) Plots, and Wiberg\nBond Index (WBI) provide conclusive evidence of the origin of stereoselectivity\nfor the intramolecular desymmetrization of the five substrates considered\nhere. The current study establishes that the SPHENOL-derived CPA catalyst\nforges enantioselective desymmetrization of 3,3-substituted oxetanes\nwith higher enantiomeric excess in comparison to previously known\nSPINOL- and BINOL-derived CPA catalysts.