A 5-step synthesis of α-alkoxymethyl-, α-siloxymethyl- and α-(carbamoyloxy)methyl-substituted enediynes 7 from type 23 β-oxo esters was developed following the strategy of Scheme 2. Specifically, the β-oxo esters 33, 36 and 38 (prepared as shown in Scheme 4) and NaH (or t-BuLi) gave Z-enolates in THF and E-enolates in DMF which were scavenged as enol triflates Z-27a-c and E-27a-c, respectively, upon treatment with triflimides 40 or 41 (Scheme 5). The Z-configurated enol triflates underwent Cacchi couplings with (trimethylsilyl)acetylene to give the pent-2-en-4-yne-1-carboxylates E-42a-c (Scheme 5). These were reduced to the corresponding aldehydes E-44a-c (Scheme 6) which were homologated with lithio(trimethylsilyl)diazomethane to furnish the desired enediynes 45a-c as pure E-isomers.
开发了一种基于方案2策略的α-烷氧甲基、α-
硅氧甲基和α-(
氨基甲酸酯氧基)甲基取代的烯二炔7的5步合成方法。具体而言,β-
酮酯33、36和38(如方案4所示制备)与NaH(或t-BuLi)在THF中生成Z-烯醇盐,在
DMF中生成E-烯醇盐,经过三
氟甲磺酰胺40或41处理后分别捕获为烯醇
三氟甲磺酸酯Z-27a-c和E-27a-c(方案5)。Z构型的烯醇
三氟甲磺酸酯与(三甲基
硅基)
乙炔进行Cacchi偶联反应,生成戊-2-烯-4-炔-1-
羧酸酯E-42a-c(方案5)。这些化合物经过还原得到相应的醛E-44a-c(方案6),再与
锂(三甲基
硅基)
重氮甲烷反应,生成纯E-异构体的目标烯二炔45a-c。