Asymmetric synthesis of (1R,8S)- and (1S,8S)-1-hydroxypyrrolizidin-3-ones from Boc-L-prolinal and (S)- and (R)-[(η5-C5H5)Fe(CO)(PPh3)(Ac)], respectively

Abstract

The aldol reaction between the aluminium enolate derived from (S)-[(η⁵-C₅H₅)Fe(CO)(PPh₃)(Ac)](S)-(3) and Boc-L-prolinal (S)-(2) gives, after deprotection and decomplexation, (1R,8S)-1-hydroxypyrrolizidin-3-one, (1), while its epimer (1S,8S)-(1) is obtained in a similar way from (R)-(3), the inherent stereocontrol of (2) being overpowered by the iron chiral auxiliary.