From Reagent to Catalyst: Dispersion-Driven Design of a General Asymmetric Transfer Hydrogenation Catalyst.

Even though chemists have long underappreciated the role of London dispersion in catalysis, its importance in determining a reaction course is now well recognized. Dispersion interactions have been shown to stabilize transition states and govern the stereoselectivity. In this context, the transfer hydrogenation of α,β-unsaturated aldehydes reported by our group via asymmetric counteranion-directed catalysis (ACDC) was revisited mechanistically. Previously, the use of an engineered Hantzsch ester featuring an isopropyl group was crucial for high enantioselectivity, suggesting London dispersion as an important stereocontrolling factor. Based on this hypothesis and the method's drawbacks (commercially unavailable Hantzsch ester, limited substrate scope, high catalyst loadings), we designed a broadly applicable second-generation catalyst system by introducing dispersion energy donors into the catalyst instead of the Hantzsch ester reagent. With the help of computational analysis, noncovalent interactions contributing to stereocontrol in the two systems were elucidated.