The C3-C17 segment of a boron containing ionophoric antibiotic aplasmomycin (1), the key intermediate in Corey's totalsynthesis of 1, was stereoselectively synthesized in an optically active form. This synthesis involved stereoselective construction of the two segments, (+)-dithiane 3 (C3-C11) and (+)-aldehyde 4 (C12-C17), based on remote controlled asymmetric reductions of the corresponding ketones