USE OF CARBOPALLADATION OF ALLENES IN THE SYNTHESIS OF POLYCYCLIC COMPOUNDS - A RAPID ACCESS TO STEROID SKELETONS

The carbopalladation of allenes in the presence of a 1,3-cycloalkanedi one enolate leads, in certain cases with good yields, to 2-substituted 1,3-cycloalkanediones with an unsaturated chain with a 1,3-butadienyl moiety (compounds 1). Under acidic conditions, these compounds can. b e readily cyclized with the formation of a cyclohexane ring if the sub stituents of the butadienyl framework exert sufficient stabilization o n the electrodeficient carbon of the transition state. This methodolog y leads in a two-step sequence to steroids with an aromatic A-ring.