Stereospecific Synthesis of the steroid hormone vitamin D3

The molecule shown has recently been synthesised by Ph.D. students in the Craig group at Imperial College. It forms part of the structure of the steroid hormone vitamin D3 (steroid numbering is shown for the structure). In the synthesis, the C8–C9 and C13–C14 bonds were formed simultaneously using an intramolecular Diels–Alder reaction. The remaining stereocentres in the structure are derived both from the chiral pool (R-pulegone) and by the use of Evans asymmetric alkylation methodology. The Craig group's intention is now to couple this intermediate with the remaining portion of vitamin D3 using a modification of the Julia olefination reaction.