Asymmetric homologation of boronic esters bearing azido and silyloxy substituents.
Asymmetric homologation of boronic esters bearing azido and silyloxy substituents.
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DOI：
10.1021/jo005522b
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发表时间：
2000-09
期刊：
影响因子：
--
通讯作者：
R. Singh;D. Matteson
中科院分区：
文献类型：
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作者：
R. Singh;D. Matteson
在硼酸酯与（二卤甲基）锂的不对称同系化中，可以结合金属阳离子的取代基往往会干扰。因此，我们进行了弱碱性的氧和氮取代基引入硼酸酯，以最大限度地提高利用这种化学的多步合成的效率。甲硅烷氧基硼酸酯不能通过直接取代有效地制备，但是（羟甲基）硼酸酯已经以通常的方式甲硅烷化。α-卤代硼酸酯向α-叠氮基硼酸酯的转化已经用叠氮化钠和作为相转移催化剂的四丁基铵盐在具有水和硝基甲烷或乙酸乙酯的两相体系中进行。这些溶剂比以前使用的二氯甲烷更安全，二氯甲烷可以与叠氮离子形成爆炸性副产物。含有甲硅烷氧基或烷氧基和叠氮基取代基的硼酸酯已被证明与（二卤代甲基）锂有效反应，导致卤代甲基有效不对称插入碳-硼键中。
In the asymmetric homologation of boronic esters with a (dihalomethyl)lithium, substituents that can bind metal cations tend to interfere. Accordingly, we undertook the introduction of weakly basic oxygen and nitrogen substituents into boronic esters in order to maximize the efficiency of multistep syntheses utilizing this chemistry. Silyloxy boronic esters cannot be made efficiently by direct substitution, but a (hydroxymethyl)boronic ester has been silylated in the usual manner. Conversion of alpha-halo boronic esters to alpha-azido boronic esters has been carried out with sodium azide and a tetrabutylammonium salt as phase-transfer catalyst in a two-phase system with water and either nitromethane or ethyl acetate. These are safer solvents than the previously used dichloromethane, which can form an explosive byproduct with azide ion. Boronic esters containing silyloxy or alkoxy and azido substituents have been shown to react efficiently with (dihalomethyl)lithiums, resulting in efficient asymmetric insertion of the halomethyl group into the carbon-boron bond.