Atropo- and Diastereoselective Construction of Tetracyclic Biphenylazepinium Salts Derived from Aminoalcohols: Use as Catalysts in Enantioselective Asymmetric Epoxidation

A range of new biphenylazepinium
salt organocatalysts effective
for asymmetric epoxidation has been developed incorporating an additional
substituted oxazolidine ring, and providing improved enantiocontrol
in alkene epoxidation over the parent structure. Starting from enantiomerically
pure aminoalcohols, tetracyclic iminium salts were obtained as single
diastereoisomers through an atroposelective oxazolidine formation.