A tandem radical macrocyclisation-transannular cyclisation approach towards the taxanes
作者:Stephen A. Hitchcock、Stephen J. Houldsworth、Gerald Pattenden、David C. Pryde、Nicholas M. Thomson、Alexander J. Blake
DOI:10.1039/a805268i
日期:——
Separate treatment of the iodotrienedione 19 and the iododienynedione 38 with Bu3SnH–AIBN produces the corresponding taxane ring systems 25 (25–30%) and 56 (50–60%) respectively by way of tandem radical macrocyclisation-radical transannular cyclisations. By contrast the analogous iodopolyenones 61, 63, 65a, 66a, 86a and 87a, together with the corresponding iodoenynones 39a and 59 failed to undergo similar tandem radical reactions, and instead gave products resulting from direct reduction of the carbon–iodine bonds in these substrates. The structures of the taxane analogues 25 and 56 followed from analysis of their NMR spectroscopic data and comparison with similar NMR data for related taxoids described in the literature. The stereochemistry of 56 was secured from an X-ray crystal structure determination of the 1,5-diol 57 produced from reduction of 56 with DIBAL.
利用Bu3SnH-AIBN单独处理iodotrienedione 19和iododienynedione 38,可以通过串联自由基大环化-跨环自由基环化反应分别生成相应的紫杉烷环系25(25-30%)和56(50-60%)。相比之下,类似的一碘多烯酮61、63、65a、66a、86a和87a,以及相应的一碘烯二酮39a和59未能经历类似的串联自由基反应,而是直接还原这些底物中的碳-碘键,生成产物。紫杉烷类似物25和56的结构是通过分析它们的NMR光谱数据,并与文献中描述的相关紫杉烷的类似NMR数据进行比较来确定的。通过使用DIBAL还原56得到的1,5-二醇57的X射线晶体结构分析,确定了56的立体化学。