A Novel, Versatile D→BCD Steroid Construction Strategy, Illustrated by the Enantioselective Total Synthesis of Estrone

A general steroid synthesis is presented that relies on prior formation of three stereogenic centers (C8, C13, and C14) on a D ring template, followed by C- and B-ring cyclizations. The assembly of the key D ring template, achieved by a 3-component conjugate addition/alkylation process, allows introduction of structural variety as required. The method is illustrated by the total synthesis of estrone via a C-ring closing metathesis and a B-ring Heck cyclization.