Synthesis of enantiopure estrone via a double Heck reaction

An novel efficient catalytic approach to steroids by a double Heck reaction of the vinyl bromides 2 and the CB-building block 3 is presented. The new estrogen analogues la and 1b are formed via 23a and 23b in a highly regio- and stereoselective manner in good yields. They contain a cis-BC ring junction and two double bonds in the 6,7- and the ll,12-positions which can be functionalized in a selective way. Inter alia, homogeneous hydrogenation with (PPh(3))(3)RhCl to give 28 followed by hydrogenation with 1,4-cyclohexadiene in the presence of palladium affords the known estradiol derivative 29a in 76% yield which can easily be transformed into estrone 31.