Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamada-oka, Suita, Osaka, 565-0871 Japan.
Chem Asian J. 2012 Aug;7(8):1925-33. doi: 10.1002/asia.201200234. Epub 2012 May 25.
Nucleophilic substitution at the anomeric positions of tetrahydropyranyl (THP) and related carbohydrate-derived esters that proceeded through pyridinium-type salt intermediates have been developed. Treatment of the 6-substituted α-acetoxy-tetrahydropyrans with TMSOTf (TMS=trimethylsilyl) and 2-substitutited pyridines, such as 2-p-tolylpyridine and 2-methoxypyridine, led to the efficient generation of cis-pyridinium-type salts. These salts reacted with various nucleophiles, such as alcohols, azides, and organozinc reagents, to form nucleophilic-substitution products. A characteristic feature of these processes was that they took place under mild conditions, which did not affect acid-labile protecting groups. Furthermore, the reactions that employed azides and C-nucleophiles generated 2,6-trans products with high degrees of stereoselectivity.
已开发出通过吡啶鎓盐中间体进行的四氢吡喃基（THP）和相关碳水化合物衍生酯的在糖苷位的亲核取代反应。用 TMSOTf（TMS=三甲基甲硅烷基）和 2-取代吡啶（如 2-对甲苯吡啶和 2-甲氧基吡啶）处理 6-取代的α-乙酰氧基四氢吡喃，可有效地生成顺式吡啶鎓盐。这些盐与各种亲核试剂（如醇、叠氮化物和有机锌试剂）反应，形成亲核取代产物。这些过程的一个特征是它们在温和的条件下进行，不会影响酸不稳定的保护基团。此外，使用叠氮化物和 C-亲核试剂的反应以高度的立体选择性生成 2,6-反式产物。
