作者:Sabine Laschat、Nicolai Cramer、Angelika Baro、Wolfgang Frey
DOI:10.1055/s-2003-42080
日期:——
N-Protected tropenone derivatives 3, prepared from the respective pyrroles 5 and tetrabromoacetone (6), were used as starting materials for desymmetrization by hydroboration of the C-C double bond. Hydroboration of 3a with (-)-(Ipc)2BH followed by oxidation, however, gave the desired 6-hydroxylated product 4a only in low yield due to byproduct formation. After acetalization of the carbonyl group in 3, the corresponding acetals 8 were desymmetrized with (Ipc)2BH and oxidative workup to chiral alcohols 11 in good yields with excellent enantiomeric excesses in most cases.
N-保护的热烯酮衍生物3,由相应的吡咯5和四溴乙酮(6)制备而成,被用作通过氢硼化对C-C双键进行不对称化的起始材料。然而,用(-)-(Ipc)2BH对3a进行氢硼化后,再进行氧化,得到所需的6-羟基化产物4a的产量仅很低,原因是副产物的形成。在对3中的羰基进行缩醛化后,得到相应的缩醛8,使用(Ipc)2BH进行不对称化,并通过氧化工序转化为手性醇11,在大多数情况下获得了良好的产率和优异的对映体过量。