Studies of the Mechanism and Origins of Enantioselectivity for the Chiral Phosphoric Acid-Catalyzed Stereoselective Spiroketalization Reactions.

Mechanistic and computational studies were conducted to elucidate the mechanism and the origins of enantiocontrol for asymmetric chiral phosphoric acid-catalyzed spiroketalization reactions. These studies were designed to differentiate between the S(N)1-like, S(N)2-like, and covalent phosphate intermediate-based mechanisms. The chiral phosphoric acid-catalyzed spiroketalization of deuterium-labeled cyclic enol ethers revealed a highly diastereoselective syn-selective protonation/nucleophile addition, thus ruling out long-lived oxocarbenium intermediates.

Enantioselective synthesis of piperidines through the formation of chiral mixed phosphoric acid acetals: experimental and theoretical studies.

An enantioselective intramolecular chiral phosphoric acid-catalyzed cyclization of unsaturated acetals has been utilized for the synthesis of functionalized chiral piperidines. The chiral enol ether products of these cyclizations undergo subsequent in situ enantioenrichment through acetalization of the minor enantiomer. A new computational reaction exploration method was utilized to elucidate the mechanism and stereoselectivity of this transformation.

Chiral phosphoric acid-catalyzed enantioselective and diastereoselective spiroketalizations.

Catalytic enantioselective and diastereoselective spiroketalizations with BINOL-derived chiral phosphoric acids are reported. The chiral catalyst can override the inherent preference for the formation of thermodynamic spiroketals, and highly selective formation of nonthermodynamic spiroketals could be achieved under the reaction conditions.