In order to determine the absolute configuration of 4, the TMP group of 4b was removed by IBX to afford 6 in 99% yield without loss of optical purity (Scheme 2). After benzoylation, the ee of 6 was determined and the absolute configuration of 4a was found to be S by comparison of the optical rotation sign and the retention time in the HPLC analysis of 7 with a chiral column with literature values. The absolute stereochemistry of the other products was surmised by analogy.