New bis- and tris-annulation reagents for the syntheses of CD rings of steroids, bearing a functionalized 18-methyl group, by the palladium-catalyzed cyclization
2-alkoxycarbonyl-3-vinylcyclopentanones (2), easily prepared by the palladium-catalyzed cyclization of 2-substituted 3-oxo-8-phenoxy-6-octenoates (1), are very suitable building blocks for CD rings of steroids, bearing particularly a functionalized 18-methyl group.