Syntheses of Enantiomerically Pure 2-Substituted Pyrrolidin-3-onesvia Lithiated Alkoxyallenes - An Auxiliary-Based Synthesis of both Enantiomers of the Antibiotic Anisomycin
作者:Silvia Kaden、Mirjam Brockmann、Hans-Ulrich Reissig
DOI:10.1002/hlca.200590143
日期:2005.7
The hydrochlorides of both enantiomers of the antibiotic anisomycin were prepared starting with the ‘diacetone-fructose’-substituted allene 1 and the N-Boc-protected imine precursor 2a. Addition of an excess of lithiated 1 to 2a provided a 2 : 1 mixture 3a of diastereoisomers, which were cyclized to 4a under base promotion (Scheme 2). The two diastereoisomers of 4a were separated and converted into
从“双丙酮-果糖”取代的丙二烯1和N -Boc保护的亚胺前体2a开始制备抗生素茴香霉素的两种对映异构体的盐酸盐。加入过量的锂化的1至2a提供了非对映异构体的2∶1混合物3a,其在碱促进下环化为4a(方案2)。分离两种4a的非对映异构体,并将其转化为对映体纯的吡咯烷酮-3-酮(2 R)-5a和(2 S)-5a。类似的序列产生了N-Tos保护的化合物(2 R)-5b和(2 S)-5b。将化合物5a转化为甲硅烷基烯醇醚6,并通过随后的区域和立体选择性硼氢化成吡咯烷衍生物7(方案3)。直接的官能团转化产生茴香霉素的盐酸盐9(方案3)。(2 R)系列提供天然对映异构体的盐酸盐(2 R)-9,而(2 S)系列提供对映体(2 S)-9。天然产物的总序列涉及十步,其中包含八种纯化的中间体,总产率为8%。我们对这种类型的羟基化吡咯烷类化合物的立体化学分歧方法具有很高的灵活性,应该可以轻松制备许多类似物。