Asymmetric radical cyclization leading to β-lactams: Stereoselective synthesis of chiral key intermediates for carbapenem antibiotics PS-5 and thienamycin
作者:Hiroyuki Ishibashi、Chisato Kameoka、Kazuya Kodama、Masazumi Ikeda
DOI:10.1016/0040-4020(95)00902-7
日期:1996.1
A stereoselective synthesis of β-lactams by 4-exo-trig radical cyclizations of N-[2,2-bis(phenylthio)ethenyl]-α-bromo amides bearing a chiral inductor on the nitrogen atom has been examined. Bromide 8, upon treatment with Bu3SnH in the presence of AIBN in boiling benzene, gave a mixture of (4S)-2-azetidinone 12a and its (4R)-isomer 12b in a ratio of 71:29 and 69% combined yield. Similar treatment of
已经研究了通过在氮原子上带有手性感应剂的N- [2,2-双(苯硫基)乙烯基]-α-溴酰胺的4- exo-trig自由基环化的立体选择性合成β-内酰胺的方法。溴化物8在AIBN存在下于沸腾的苯中用Bu 3 SnH处理时,得到比例为71:29和69%的(4 S)-2-氮杂环丁酮12a和(4 R)-异构体12b的混合物综合产量。用Bu 3 SnH对α-溴丁酰胺11进行类似处理,得到反式-(4 S)-2-氮杂环丁酮17a及其主要化合物(4 R)-异构体17b(70:30,77%的总收率)。在(+)-PS-5的合成中,化合物17a被转化为24,一种手性关键中间体(25)。在侧链上带有一个额外的立体生成中心[(S)-氧官能度]的溴化物28的环化以更高的(4S)-立体选择性进行,从而得到氮杂环丁酮29a作为主要产物及其(4R)-异构体29b以78:22的比例和40%的总收率。化合物29a通过氧官能度的转