Chiral construction of the estrane ring system by an intramolecular double Michael reaction

Abstract
Construction of the estrane ring system was achieved by the Intramolecular double Michael reaction as the key step. Heating of the α,β-unsaturated enone ester (18), prepared from the optically active indanone (4), with chlorotrimethylsilane, triethylamine, and zinc chloride produced three estrane derivatives (19), (22), and (25).