Stereocontrolled synthesis of two twelve-membered lactam sulfides 37 and 38 as precurors of 8, 11, 11-trimethyl-3-oxobicyclo[5.3.1]undec-8-enes constituting the A and B rins of taxane-diterpenes was achieved.The keystep involves a Diels-Alder reaction of maleic anhydride and the E-diene 18 for introduction of the requisite cis arrangement of substitutions at the C-1 and C-7 positions.The resulting adduct was converted exclusively into the lactone 21b in five steps : 1) hydrolysis, 2) iodo-lactonization, 3) BH3 reduction, 4) Zn reduction, 5) methylation.The benzyl group of 26 could be selectively removed by heating with Raney Ni(W-2) in EtOH in nearly quantitative yield without hydrogenation of the double bond.
实现了两个十二元内酰胺
硫化物 37 和 38 的立体控制合成,它们是构成
紫杉烷-二萜 A 和 B 环的 8、11、11-三甲基-3-氧代双环[5.3.1]十一碳-8-烯的前体。关键步骤是
马来酸酐和 E-二烯 18 发生 Diels-Alder 反应,在 C-1 和 C-7 位置引入必要的顺式排列取代:用 Raney Ni(W-2) 在 EtOH 中加热,可以选择性地去除 26 的苄基,几乎可以得到定量的收率,而不需要双键氢化。