Reaction of the acetals with TESOTf-base combination; Speculation of the intermediates and efficient mixed acetal formation
Reaction of the acetals with TESOTf-base combination; Speculation of the intermediates and efficient mixed acetal formation
复制标题
DOI：
10.1021/ja060328d
复制
发表时间：
2006-05-03
影响因子：
15
通讯作者：
Kita, Y
中科院分区：
文献类型：
--
作者：
Fujioka, H;Okitsu, T;Kita, Y
我们在这里报告了意想不到的高度化学选择性的脱保护的缩醛醛。用TESOTf-2，6-二甲基吡啶或TESOTf-2，4，6-三甲基吡啶在CH 2Cl 2中在0 ℃下处理来自醛的缩醛化合物，然后在相同温度下进行H2O处理，导致缩醛官能团转化为醛官能团。该反应具有通用性，适用于许多缩醛化合物。使用各种碱的研究揭示了反应，并达到了TESOTf-碱的最佳组合。它是非常温和和高度化学选择性和进行弱碱性条件下。然后，许多官能团，如烯丙醇，甲硅烷基醚，乙酸酯，甲基醚，三苯基甲基（Tr）醚，1，3-二硫戊环，甲酯，和叔丁基酯可以在这些条件下存活。此外，这种方法可以选择性地脱保护的缩醛在缩酮的存在下作为最典型的特征，虽然这种化学选择性是难以实现的其他先前报道的方法。包括MS和NMR研究的反应的详细研究揭示了确定中间体，吡啶鎓型盐的结构的反应机理。这些中间体具有弱的亲电性，并成功地应用于高收率的混合缩醛的有效形成。
We report here unexpected highly chemoselective deprotection of the acetals from aldehydes. Treatment of acetal compounds from aldehydes with TESOTf-2,6-lutidine or TESOTf-2,4,6-collidine in CH2Cl2 at 0 degrees C followed by H2O workup at the same temperature caused the conversion of the acetal functions to aldehyde functions. The reaction had generality and was applied to many acetal compounds. Study using various bases revealed the reaction and reached the best combination of TESOTf-base. It was very mild and highly chemoselective and proceeded under weakly basic conditions. Then, many functional groups such as allyl alcohol, silyl ether, acetate, methyl ether, triphenylmethyl (Tr) ether, 1,3-dithiolane, methyl ester, and tert-butyl ester could survive under these conditions. Furthermore, this methodology could selectively deprotect the acetals in the presence of ketals as the most characteristic feature, although this chemoselectivity is difficult to achieve by other previously reported methods. A detailed study of the reaction including MS and NMR studies revealed the reaction mechanism for determining the structures of the intermediates, pyridinium-type salts. These intermediates had a weak electrophilicity and were successfully applied to the efficient formation of the mixed acetals in high yields.