Control of Regioselectivity in the Transition‐Metal‐Catalysed Conjugate Additions of Alkylaluminium Compounds and Methyltitanium Ate Complexes to Androsta‐1,4‐diene‐3,17‐dione

By a variation of the nature of the reagent system conjugate addition to the cross‐conjugated steroidal dienone 1 occurs selectively either at C‐1 or at the sterically hindered C‐5. With Me3Al or Me4AlLi in the presence of catalytic amounts of Cu1 salts, a high regioselectivity (up to 97:3) in favour of position 1 is achieved. Application of ate complexes of aluminium and titanium in the presence of Ni(acac)2 as catalyst, however, leads to a reversal of the regioselectivity in favour of position 5 (up to 11:89). Aluminium and titanium ate complexes are efficient reagents in the Ni(acac)2‐catalysed conjugate addition to sterically hindered enones.