An attempt to synthesize the cyclohexane core of antibiotic abyssomicin C is described. The initial, protecting group-free approach (relying on internal protection) failed and had to be modified, in order to allow for efficient deprotection of the acid-sensitive cyclization precursor in the penultimate synthetic step. Thus, a pyranoside structural unit was used as a latent lactone/ester functionality, which was deprotected via thioacetalization/hydrolysis/oxidation sequence, to give the ?-valerolactone-type cyclization precursor. Unfortunately, the key cyclization reaction was not feasible, even after structural modification of the cyclization precursor. Reluctance towards cyclization turned out to be a general property of (at least some) ?7-unsaturated esters, which required the development of a new strategy for this type of transformation.
本文介绍了合成抗生素阿比索米星 C 环己烷核心的尝试。最初的无保护基方法(依靠内部保护)失败了,必须进行修改,以便在倒数第二个合成步骤中对酸敏感的环化前体进行有效的脱保护。因此,吡喃糖苷结构单元被用作潜伏的内酯/酯官能团,通过硫代乙醛化/水解/氧化顺序对其进行脱保护,从而得到戊内酯型环化前体。遗憾的是,即使对环化前体进行了结构改造,关键的环化反应仍不可行。不愿意发生环化反应原来是(至少是某些)?