Stereoselective synthesis of novel 19-nor-steroids by a double Heck reaction

The estrane 4 was synthesized by two successive Heck reactions starting from enantiopure 2 and the cyclohexenone 5, which contains a (Z)-bromovinyl group. The first intermolecular Pd-catalyzed reaction leads to 10 in a highly regio-and diastereoselective manner. Transformation of the enone 10 to give the corresponding enol triflate 14 followed by an intramolecular Heck reaction affords the cyclized product 4 with an unusual cis-junction of the rings B and C in high yield.