ent-Kaurene全碳骨架中AB环系的不对称合成

Asymmetric Synthesis of AB Rings in ent-Kaurene Carbon Framework

本课题组前期利用多样性导向合成策略完成ent-kaurene天然产物Xerophilusin I、Neolaxiflorin L、Eriocalyxin B、15-epi-Enmelol全合成工作,为完成该类天然产物的不对称合成,对Horner-Wadsworth-Emmons反应进行了优化,改善了反应的区域选择性,在酸性条件下后处理,将Z/E混合物转化为单一Z构型.基于温和的酸性条件实现了单一构型的转化,提出了氢键辅助的Michael加成/retro-Michael消除的机理猜想.发展了Cu(OTf)_(2)催化的不对称Diels-Alder反应:以烯醇硅醚的双烯体3、β-酮酸酯1为亲双烯体,在噁唑啉为手性配体的条件下,以65%的收率和>19∶1dr值完成AB环的构建.

The total synthesis of ent-kaurene natural products of Xerophilusin I,Neolaxiflorin L,Eriocalyxin B,15-epi-Enmelol completed by diversity-oriented synthesis strategy.In this paper,the regioselectivity of Horner-Wadsworth-Emmons reaction was optimized,and a single Z configuration was transformed from Z/E mixture under acidic condition.Based on the conversion of a single configuration under mild acidic conditions,a mechanism for hydrogen bond-assisted Michael addition/retro-Michael elimination is proposed.The asymmetric Diels-Alder reaction with silylenol ether dienyl 3 andβ-ketoate 1 as dienophile was developed.Using Cu(OTf)_(2)as Lewis acid and oxazoline as chiral ligand,AB-ring-skeleton was constructed with 65%yield and>19∶1 dr value.