Synthesis, structure and comparative stability of β-hydrazono, oximino methyl ether and imino boronates
Synthesis, structure and comparative stability of β-hydrazono, oximino methyl ether and imino boronates
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DOI：
10.1039/b004573j
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发表时间：
2000-01-01
期刊：
影响因子：
--
通讯作者：
Whiting, A
中科院分区：
文献类型：
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作者：
Mears, RJ;Sailes, HE;Whiting, A
β-腙和肟基醚硼酸酯是通过相应的甲基腙或肟甲基醚的顺序锂化，然后与碘甲基硼酸酯（通常以频哪醇酯的形式）反应来制备的。所得产品具有对比鲜明的水解稳定性。 β-亚肼基硼酸酯对分子内催化水解高度敏感，通常可以高产率提供相应的 β-酮硼酸酯； β-肟基醚硼酸盐是稳定的。硅胶色谱法并显示E-Z-异构化的证据。 β-肟基醚的稳定纯手性硼酸酯衍生物可以通过双酯交换过程，通过二乙醇胺介导的频哪醇酯交换，然后用纯手性二醇进行二乙醇胺酯水解-再酯化过程来容易地制备。 β-亚氨基硼酸酯可以通过相应的β-酮硼酸酯与伯胺的缩合原位生成，然而所得的亚胺官能团具有高度水解稳定性，并且不能以纯形式分离。
beta-Hydrazono and oximino ether boronates have been prepared by the sequential lithiation of the corresponding methyl hydrazone or oxime methyl ether, followed by reaction with an iodomethylboronate ester, typically in the form of the pinacol ester. The resulting products have contrasting hydrolytic stabilities. beta-Hydrazono boronates are highly sensitive to intramolecularly catalysed hydrolysis, providing the corresponding beta-keto boronates in generally high yields; beta-oximino ether boronates are stable to. silica gel chromatography and show evidence of E-Z-isomerisation. Stable homochiral boronate ester derivatives of beta-oximino ethers can be readily prepared by a double transesterification process, via a diethanolamine-mediated pinacol ester exchange, followed by diethanolamine ester hydrolysis-reesterification process with a homochiral diol. beta-Imino boronates can be generated in situ by condensation of the corresponding beta-keto boronate with a primary amine, however the resulting imine function is highly hydrolytically unstable and cannot be isolated in a pure form.