Asymmetric oxidation of cyclobutanones: modification of the Sharpless catalyst

Abstract

Oxidation of prochiral and racemic cyclobutanones with t-BuOOH and Ti–TADDOL-based complexes afforded lactones in up to 44% ee. The enantioselectivity of the reaction clearly depends on the amount of the reagent and the highest enantioselectivities were obtained with stoichiometric amounts of the complex. Modification of the TADDOL structure and use of the mixed complex derived from TADDOL and a tartaric ester led to more reactive but less selective oxidation systems.