Enantiopure <i>N</i>-Acyldihydropyridones as Synthetic Intermediates: Asymmetric Syntheses of Indolizidine Alkaloids (−)-205A, (−)-207A, and (−)-235B
作者:Daniel L. Comins、Donald H. LaMunyon、Xinghai Chen
DOI:10.1021/jo971448u
日期:1997.11.1
addition of 4-(benzyloxy)butylmagnesium bromide, and vinyl triflate formation provided 13 in a stereoselective fashion. Catalytic reduction of the vinyl triflate moiety, simultaneous cleavage of the benzyl ether and Cbz groups, and cyclization to give amino alcohol 14 was effected via a one-pot reaction. Oxidation of 14 with the Dess-Martin reagent gave a 97% yield of amino aldehyde 4. Synthesis of each
吲哚并立定生物碱(-)-205A,(-)-207A和(-)-235B的简明不对称合成是在11个步骤中以高度立体控制完成的。将4-(1-丁烯基)溴化镁加到1-酰基吡啶鎓盐5中,该盐由4-甲氧基-3-(三异丙基甲硅烷基)吡啶和(+)-反式-2-(α-枯基)环己醇的氯甲酸酯原位制备产生91%的非对映异构纯二氢吡啶酮6。6的氧化裂解和随后的还原提供了81%产率的醇7。除去手性助剂和TIPS组(NaOMe; 10%HCl),用BnOCOCCl进行N-酰化,并用NCS / Ph(3)P处理,得到氯化物10。在C-3处甲基化,铜介导的共轭加成4- (苄氧基)丁基溴化镁和三氟甲磺酸乙烯酯的形成以立体选择性方式提供了13。三氟甲基乙烯基部分的催化还原,通过一锅法反应同时裂解苄基醚和Cbz基团,以及环化得到氨基醇14。用Dess-Martin试剂氧化14时,氨基醛4的产率为97%。三种标题生物碱中的每一种的合