An Experimental and Theoretical Study of the Asymmetric Lithiation of 1,2,3,5,6,7-Hexahydro-3a,4a-diazacyclopenta[<i>def</i>]phenanthren-4-one
作者:Costa Metallinos、Travis Dudding、Josh Zaifman、Jennifer L. Chaytor、Nicholas J. Taylor
DOI:10.1021/jo062244t
日期:2007.2.1
ne to undergo asymmetric lithiation with (−)-sparteine is circumvented by use of a urea functionality as the directing group. Asymmetric lithiation followed by electrophile quench gives products substituted α to nitrogen in better yield (17−30%) but slightly lower enantiomeric ratio (er 84:16) than analogous lithiation of N-Boc-piperidine (er 87:13). Computational studies at the MP2/6-316(d)//B3LYP/6-316(d)
通过使用尿素官能团作为指导基团,避免了双-N -Boc保护的八氢菲咯啉无法与(-)-天冬氨酸进行不对称锂化。不对称锂化后再进行亲电淬灭,与N -Boc-哌啶的类似锂化(er 87:13)相比,以更好的收率(17-30%)得到的产品将α取代为氮,但对映体比率(er 84:16)略低。在MP2 / 6-316(d)// B3LYP / 6-316(d)水平上的计算研究表明,手性赤道S-氢优先于pro- R被去除。氢,其过渡态活化能之差为1.26 kcal / mol,对应于89:11的预计er。通过对映异构体富集的α-甲基取代产物制备的芳基二溴化物的单晶X射线分析证实了预计的反应立体化学。