Stereoselective Organocatalytic Alkylations with Carbenium Ions

Diastereoselective S(N)1-type reactions have been known for many years and have been used in the synthesis of many natural products. It has recently been shown that chiral nucleophiles, obtained using organocatalytic methodologies, can react with highly reactive carbenium ions in a stereoselective fashion. Based on this, carbenium ions can be applied in asymmetric catalytic reactions. 1 Introduction 1.1 Reaction of Ferrocenyl Alcohols with Lewis Acids 2 Reaction of Alcohols 'on Water' 2.1 Stability of Carbenium Ions and the Mayr Scale 3 Organocatalytic Stereoselective S(N)1-Type Reactions of Aldehydes and Isolated Carbenium Ions 3.1 Attempts at the Related Asymmetric S(N)1-Type alpha-Alkylation of Ketones 3.2 Organocatalytic Stereoselective S(N)1-Type Reactions under Oxidative Conditions 4 Organocatalytic S(N)1-Type Reactions Involving Lewis Acids 5 Alkylation of Aldehydes Made Simple with the Benzodithiolylium Ion 6 Organocatalytic S(N)1-Type Reactions Involving Bronsted Acids 7 S(N)1-Type Reactions Promoted by Chiral Thioureas 8 Conclusion and Perspectives