A Novel Method for Inside Selective Silylation of 1,2-Diols.
A Novel Method for Inside Selective Silylation of 1,2-Diols.
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1,2-二醇内部选择性硅烷化的新方法。
DOI：
10.1021/jo9722358
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发表时间：
1998
期刊：
影响因子：
--
通讯作者：
I. Kuwajima
中科院分区：
文献类型：
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作者：
K. Tanino;Tadashi Shimizu;M. Kuwahara;I. Kuwajima
硅基对于羟基的保护是非常重要的1，多元醇的位置选择性硅基化在有机合成中经常被使用。由于通常的硅化条件总是影响对受阻较小的羟基的选择性保护，2 1，2-烷基二醇在内部的选择性硅化通常需要多步转化。例如，2-硅氧基-1-烷醇可以由相应的二元醇通过1-羟基的酯化、2-羟基的硅烷化和酯部分的水解制得(方案1)。本文介绍了一种新的1，2-烷基二醇内羟基一锅硅烷化反应方法。关于苄基醚、3叔丁基醚、4甲氧基甲基醚、5或苯甲酸酯对1，2-烷基二醇的内部选择性保护，已有多篇报道。6值得注意的是，所有这些例子都涉及五元中间体的区域选择性切割，即环缩醛、邻酯或磷戊烷。另一方面，关于前面描述的1-氧杂-2-硅环戊烷衍生物的化学，7我们对由亲核试剂引起的环硅醚的开环反应感兴趣。我们设想用亲核试剂处理1，3-二氧杂-2-硅环戊烷衍生物可能会发生区域选择性的环裂解，从而得到相应的2-硅氧基-1-烷醇。8由于五元环硅醚很容易被硅胶柱层析水解，9希望在一锅中同时进行这些醚的制备和开环反应。用二烷基硅基二氯10或二氟化双氟11和胺进行1，2-烷基二醇的硅烷化反应的传统方法不适用于此目的，因为生成的铵盐将作为质子供体。我们发现，1，2-己二醇与1当量的丁基锂在四氢呋喃中反应，然后与二叔丁基氯硅烷反应，得到了具有放氢作用的环状硅醚。溶液的处理
Silyl groups are of great importance for protection of a hydroxy group, 1 and site-selective silylation of polyols has frequently been used in organic synthesis. Since usual silylation conditions always effect selective protection of the less hindered hydroxy group, 2 inside selective silylation of a 1, 2-alkanediol generally requires multistep transformations. For example, a 2-siloxy-1-alkanol can be prepared from the corresponding diol through esterification of the 1-OH group, silylation of the 2-OH group, and hydrolysis of the ester moiety (Scheme 1). In the present paper, we describe a novel method for one-pot silylation of the internal hydroxy group of a 1, 2-alkanediol. There are several reports concerning inside selective protection of 1, 2-alkanediols by benzyl ethers, 3 tert-butyl ethers, 4 methoxymethyl ethers, 5 or benzoates. 6 It is noteworthy that all of these examples involve regioselective cleavage of five-membered intermediates, namely, cyclic acetals, ortho esters, or phospholanes. On the other hand, in relation to the chemistry of 1-oxa-2-silacyclopentane derivatives described previously, 7 we became intrigued by ring-cleavage reactions of cyclic silyl ethers induced by nucleophiles. We envisioned that treatment of a 1, 3-dioxa-2-silacyclopentane derivative with a nucleophile might effect regioselective ring cleavage to give the corresponding 2-siloxy-1-alkanol. 8Since five-membered cyclic silyl ethers easily undergo hydrolysis by silica gel column chromatography, 9 it was desired to carry out both the preparation and ring cleavage reaction of these ethers in one pot. The conventional methods for silylation of 1, 2-alkanediols by using dialkylsilyl dichloride10 or ditriflate11 and amines are unsuitable for this purpose because the resulting ammonium salt would serve as a proton donor. We found that the reaction of 1, 2-hexanediol with 1 equiv of butyllithium followed by di-tert-butylchlorosilane in THF affords the desired cyclic silyl ether with the evolution of hydrogen. Treatment of the solution