Mechanistic, crystallographic, and computational studies on the catalytic, enantioselective sulfenofunctionalization of alkenes

The stereocontrolled introduction of vicinal heteroatomic substituents into organic molecules is one of the most powerful ways of adding value and function. Although many methods exist for the introduction of oxygen- and nitrogen-containing substituents, the number of stereocontrolled methods for the introduction of sulfur-containing substituents pales by comparison. Previous reports from our laboratories have described sulfenofunctionalizations of alkenes that construct carbon–sulfur bonds vicinal to carbon–oxygen, carbon–nitrogen or carbon–carbon bonds with high levels of diastereospecificity and enantioselectivity. This process is enabled by the concept of Lewis-base activation of Lewis acids, which provides activation of Group 16 electrophiles. To provide a foundation for the expansion of substrate scope and improved selectivities, we have undertaken a comprehensive study of the catalytically active species. Insights gleaned from kinetic, crystallographic and computational methods have led to the introduction of a new family of sulfenylating agents that provide significantly enhanced selectivities. Kinetic, X-ray crystallographic and computational studies have enabled the formulation of a comprehensive mechanistic picture of the enantioselective sulfenofunctionalization reaction of alkenes and a stereochemical model for the origin of the enantioselectivity. The experiments resulted in the development of 2,6-dialkylaryl sulfenylating agents, improving the enantioselectivity of the reaction to >99:1 for γ-alkenols.