61. The Enantioselective Synthesis of (+)-Estradiol from 1,3-Dihydrobenzo[c]thiophene-2,2-dioxide by Successive Thermal SO₂-Extrusion and Cycloaddition Reactions. Preliminary communication
    Oppolzer, W.; Roberts, D. A.
    Helv. Chim. Acta 1980, 63, 1703-1705

The optically pure steroid (+)-15 has been synthesized from the easily accessible (+)-carboxylic acid 11 by a sequence of 7 steps in 50% overall yield. The key steps are the regioselective deprotonation/alkylation 7+13 → 14 and the thermal SO₂-extrusion/cycloaddition 14 → 15(Scheme 3). The compound (+)-15 has been readily converted to the naturally occurring (+)-estradiol (17) in 60% yield.

DOI : 10.1002/hlca.19800630638