Asymmetric Oxidation of a Dihydrothienopyrimidine

A robust catalytic asymmetric oxidation of prochiral sulfide <b>1</b> has been achieved by the use of a chiral titanium–hydrobenzoin complex. Reproducible reaction conditions were identified by screening reaction parameters and DOE optimization. The enantioselectivity was found to be mostly influenced by the amount of water and the time the catalyst was aged before addition of the sulfide