From an ent-Estrane, through a nat-Androstane, to the Total Synthesis of the Marine-Derived Δ^8,9-Pregnene (+)-03219A

The total synthesis of (+)-03219A, a rare Δ^8,9-pregnene isolated from the marine-derived Streptomyces sp. SCSIO 03219, is described that is based on a series of transformations that enable progression from epichlorohydrin to an ent-estrane, then conversion to a nat-androstane, and finally establishment of the natural product target. Key to the success of these studies was implementation of two rearrangement processes to formally invert the quaternary center at C13 and establish the C10 quaternary center.