Stereoselective Synthesis of a Key Intermediate of Sanfetrinem by Means of a Chelated Tin(IV) Enolate
作者:Tino Rossi、Carla Marchioro、Alfredo Paio、Russell J. Thomas、Paola Zarantonello
DOI:10.1021/jo962095m
日期:1997.3.1
(2S)-2-Methoxycyclohexanone [(2S)-6], reacts with the 4-acetoxyazatidinone 3a in the presence of SnCl4 and a tertiary amine base (such as N,N-diisopropylethylamine) to give the ketoazetidinone 5 (a key intermediate in the synthesis of the broad-spectrum antibiotic sanfetrinem 2a) with high yield and diastereoselectivity. Low-temperature NMR studies of the reaction indicated the formation of a 1:1 chelate complex 11 between SnCl4 and (2S)-6 which, on addition of the base is transformed into the highly reactive chelated tin enolate 12. The formation of compound 11 has been confirmed by single-crystal X-ray analysis. The high diastereoselectivity observed is believed to derive from an open transition state where the chelated SnCl4 amplifies the stereochemical influence of the methoxy group. This reaction offers considerable advantages over all existing syntheses of the ketoazetidinone 5 and is currently under evaluation for inclusion in the industrial synthesis of sanfetrinem.
(2S)-2-甲氧基环己酮 [(2S)-6] 在 SnCl4 和叔胺碱(如 N,N-二异丙基乙基胺)的存在下与 4-乙酰氧基氮杂环丙酮 3a 反应,以高产率和优异的对映选择性生成酮氮杂环丁酮 5(广谱抗生素桑飞特罗姆 2a 合成中的关键中间体)。低温核磁共振研究表明,反应中形成了 SnCl4 与 (2S)-6 之间的 1:1 螯合物 11,当加入碱后,该化合物转化为具有高度反应性的螯合 Tin 烯醇化物 12。单晶 X 射线分析证实了化合物 11 的形成。观察到的高对映选择性被认为是由于开放的过渡态中螯合的 SnCl4 放大了甲氧基的立体化学影响。与现有的酮氮杂环丁酮 5 的所有合成方法相比,此反应具有显著优势,目前正在评估其是否可用于桑飞特罗姆的工业合成。