Asymmetric synthesis of (diene)Fe(CO)3 complexes by a catalytic enantioselective alkylation using dialkylzincs

The reaction of meso-(2,4-hexadien-1,6-dial)Fe(CO)(3) complex 1 with several alkylzincs in the presence of 50 mol% of (S)-(+)- diphenyl(diphenyl(1-methylpyrrolidin-2-yl)methanol 6a proceeded with high enantiotopic group- and diastereotopic Face-selectivity to give (2R,6S)-alcohol complexes 2a-c as major products, except in the case with dimethylzinc (>90% de and >98% ee). On the other hand, the methylation of 1 with Me2Zn proceeded with high enantioselectivity by adding 1.8 equiv. of Ti(Oi-Pr)(4) in the presence of 3 mol% of (S,S)-1,2-bis(trifluoromethylsulfonamide)cyclohexane 9a (82% de, 96% ee). The enantioselective alkylation was also applied to the kinetic resolution of racemic (sorbic aldehyde)Fe(CO)(3) complex 10. (C) 1998 Elsevier Science Ltd. All rights reserved.