Unexpected highly chemoselective deprotection of the acetals from aldehydes and not ketones: TESOTf-2,6-lutidine combination.
Unexpected highly chemoselective deprotection of the acetals from aldehydes and not ketones: TESOTf-2,6-lutidine combination.
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DOI：
10.1021/ja046103p
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发表时间：
2004-09
影响因子：
15
通讯作者：
H. Fujioka;Y. Sawama;Nobutaka Murata;Takashi Okitsu;Ozora Kubo;S. Matsuda;Y. Kita
中科院分区：
文献类型：
--
作者：
H. Fujioka;Y. Sawama;Nobutaka Murata;Takashi Okitsu;Ozora Kubo;S. Matsuda;Y. Kita
缩醛官能团被认为是羰基的良好保护基团。尽管已经开发了许多将缩醛脱保护成羰基官能团的方法，但是没有可以在缩酮存在下将缩醛脱保护的方法，因为通常的酸性或自由基反应更容易通过来自缩酮的更稳定的阳离子或自由基中间体发生。另一方面，这一新方法可以与以前报告所述的方法相反的方式进行。也就是说，该方法可以在缩酮存在下使脂族缩醛脱保护。反应条件对于甲硅烷基化是常见的，即，TESOTf-2，6-二甲基吡啶组合。尽管TMSOTf-2，6-二甲基吡啶组合也可以使缩醛脱保护，但它在缩醛从醛和酮脱保护中缺乏化学选择性。用TESOTf和2，6-二甲基吡啶在CH 2Cl 2中处理缩醛，然后用H2O处理，得到相应的醛。当然，具有缩醛和羟基官能团的化合物提供了通过醇的通常甲硅烷基化和缩醛的脱保护获得的化合物而没有任何问题。然而，在缩醛从醛的转化反应期间，未观察到缩酮从酮的脱保护。这种化学选择性在同一分子中具有缩醛和缩酮的化合物的反应中得到证实。在这两种情况下，缩醛官能团被脱保护以得到具有完整缩酮的醛。此外，在本文所述的条件下，许多官能团（例如甲氧基、乙酰氧基、烯丙醇和甲硅烷基氧醚）都是完整的。这种方法非常温和，适用于许多化合物。
Acetal functions are recognized as good protecting groups of carbonyl groups. Although many deprotecting methods of acetals to carbonyl functions have already been developed, there is no methodology which can deprotect acetals in the presence of ketals because the usual acidic or radical reactions occur more easily via the more stable cationic or radical intermediates from the ketals. On the other hand, this new method can proceed in a reverse manner to that described in previous reports. That is, the method can deprotect aliphatic acetals in the presence of ketals. The reaction condition is common for silylation, i.e., the TESOTf-2,6-lutidine combinations. Although the TMSOTf-2,6-lutidine combination can also deprotect acetals, it lacks chemoselectivity in deprotection of the acetals from aldehydes and ketones. The treatment of acetals with TESOTf and 2,6-lutidine in CH2Cl2 followed by a H2O workup gave the corresponding aldehydes. Of course, the compounds, which have both acetal and hydroxyl functions afforded the compounds obtained by the usual silylation of an alcohol and deprotection of an acetal without any problem. However, deprotection of the ketals from ketones was not observed during the conversion reaction of acetals from aldehydes. This chemoselectivity was confirmed in the reactions of the compounds that have the acetal and ketal in the same molecule. In both cases, the acetal functions were deprotected to give aldehydes with intact ketals. Furthermore, under the conditions described here, many functional groups such as methoxy, acetoxy, allyl alcohol, and silyloxy ether are intact. This method is very mild and available for many compounds.