Homogeneous coupling and carbonylation reactions of steroids possessing iodoalkene moieties. Catalytic and mechanistic aspects

Both 17-iodo-16-ene and 6-iodo-5-ene functionalities of androstane derivati ves (17-iodo-4-aza-5 alpha-androsta-16-en-3-one (1), 6-iodo-17-methoxycarbo nyl-4-aza-androsta-5,16-dien-3-one (2), 6,17-diiodo-4-aza-androsta-5,16-die n-3-one (3), 17-iodo-androsta-16-ene (4), 6-iodo-17-(N,N-pentamethylene-car boxamido)-4-aza-androst-5,16-dien-3-one (5)) react with vinyl-tributyltin i n a Stille reaction. However, palladium-catalysed carbonylation takes place selectively in position 17. The oxidative addition of 'iodo-vinyl' functio nalities to in situ formed Pd(0)-triphenylphosphine species was observed by P-31-NMR spectroscopy. Dinuclear palladium(II) steroidal alkenyl or acyl s pecies were detected under argon or carbon monoxide, respectively, when the 6-iodo-5-ene functionality (in ring B) was attached to a lactam moiety (ri ng A) in the steroidal substrate. In addition to monomeric species, some ol igomeric ones were also formed depending on the reaction conditions (gas at mosphere, solvent). (C) 1999 Elsevier Science S.A. All rights reserved.