The enantioselective synthesis of seven pyrrolizidine diols has been accomplished from a single, readily available intermediate. The key step of this general scheme involves an acetoxy-directed acyliminium ion-ketene dithioacetal cationic cyclization to give the optically active l-azabicyclo [3.3. 0] octane 14, from which the pyrrolizidines 1-7 were prepared. The pyrrolizidine diols in the 7s series were obtained by adjusting the oxidation level and ...
