Asymmetric oxidation of cyclobutanones: modification of the Sharpless catalyst

Oxidation of prochiral and racemic cyclobutanones with t-BuOOH and Ti-TADDO L-based complexes afforded lactones in up to 44% ee. The enantioselectivity of the reaction clearly depends on the amount of the reagent and the highe st enantioselectivities were obtained with stoichiometric amounts of the co mplex. Modification of the TADDOL structure and use of the mixed complex de rived from TADDOL and a tartaric ester led to more reactive but less select ive oxidation systems. (C) 1998 Elsevier Science Ltd. All rights reserved.