ASYMMETRIC-SYNTHESIS OF (1R,8S)-1-HYDROXYPYRROLIZIDIN-3-ONES AND (1S,8S)-1-HYDROXYPYRROLIZIDIN-3-ONES VIA THE ALDOL REACTION BETWEEN N-BOC-(S)-PROLINAL AND CHIRAL ACETATE ENOLATE EQUIVALENTS DERIVED FROM (S)-[(ETA-5-C5H5)FE(CO)(PPH3)COCH3] AND (R)-[(ETA-5-C5H5)FE(CO)(PPH3)COCH3]

Syntheses of both title compounds have been achieved with excellent stereocontrol using chiral acetate enolate equivalents derived from the iron acetyl complex [(eta(5)-C5H5)Fe(CO)(PPh3)COCH3]. The different diastereoselectivities in the two syntheses are rationalised in terms of the concept of double asymmetric induction and the transition state models for the aldol reactions of such enolates are discussed.