Synthesis of aromatic steroids by palladium(0) coupling and electrocyclic ring closure

Abstract

The naphthylcyclopentenone (1a) is reduced with sodium borohydride to the alcohol (1c). This cyclises when heated in xylene to give the estra-1,3,5(10),8(14),9(11)-pentaen-17-ols (2). The 17α-alcohol (2a) is the major component of the mixture and is isolated pure. When the cyclopentanol (1c) is heated in bromobenzene, the products are the estra-1,3,5(10),8,14-pentaen-17-ols (3b) and (3c), together with a hydrocarbon, the 17-methylcyclopenta[a] phenanthrene (5a). This compound is probably formed from the alcohols (2) or (3) by an acid-catalysed 1,2 methyl shift. The corresponding cyclopentenol (1d) has been prepared from the bromonaphthalene (6) and 3-(t-butyldimethylsilyloxy)-1-iodocylopentene (7) by palladium(0)-catalysed cross coupling. This cyclises in bromobenzene to give the cyclopentaphenanthrene (5b) and the alcohols (3d) and (3e). The known estrone intermediate (9) has been prepared by oxidation of these alcohols.