Lewis Base Catalysis: A Platform for Enantioselective Addition to Alkenes Using Group 16 and 17 Lewis Acids (n → σ*)

The concept of "Lewis base activation of Lewis acids" has been successfully exploited for the development of myriad catalytic enantioselective reactions, specifically involving Group 14 Lewis acids. Numerous studies have demonstrated the formation of 3C-4E hypervalent bonds between a Lewis base and a Group 16 or 17 Lewis acid. This chapter details the advances in the field of Lewis base-catalyzed enantioselective alkene functionalizations. It presents the advances in seleno-, sulfeno-, and halofunctionalizations, respectively. Electrophilic selenenylation of alkenes is an established method for the rapid introduction of vicinal functional groups often with concomitant formation of rings and stereocenters. This process is characterized by the anti-addition of a nucleophile and selenium electrophile to an isolated double bond. The stereochemical course and mechanism of the electrophilic sulfenylation reaction of alkenes has been studied extensively. By analogy to selenofunctionalization, an "iranium" ion intermediate that preserves the configuration of the alkene is proposed to account for the high antistereospecificity.