Lithium enolates from a (-)-quinic acid-derived cyclohexanone with a β-alkoxy leaving group:: regioselective preparation and evaluation of enolate stability towards β-elimination
Lithium enolates from a (-)-quinic acid-derived cyclohexanone with a β-alkoxy leaving group:: regioselective preparation and evaluation of enolate stability towards β-elimination
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DOI：
10.1016/j.tetlet.2004.01.148
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发表时间：
2004-03-15
影响因子：
1.8
通讯作者：
Wünnemann, S
中科院分区：
文献类型：
--
作者：
Murray, LM;O'Brien, P;Wünnemann, S
（-）-奎宁酸衍生酮{2S，3S,4aR,8R,8aS)-8-[（叔丁基（二甲基）硅基）氧]-2,3-二甲氧基-2,3-二甲基六氢-1,4-苯并二恶-6(5H)- 1}在-78度用六甲基二叠氮化锂（LHMDS）脱质子得到一个区域异构体烯酸酯。区域控制由轴向β -硅氧基取代基控制，得到的烯酸锂在高达-40度的温度下对β -消除是稳定的。结果表明，在0°c温度下，用2.1等量的LHMDS可方便地消除轴向β -硅氧基，而赤道型β -烷氧基更不易被消除。用手性锂酰胺碱推翻了LHMDS对酮去质子化的固有区域选择性。(C) 2004 Elsevier Ltd.版权所有。
Deprotonation of a (-)-quinic acid-derived ketone {2S,3S,4aR,8R,8aS)-8-[(tert-butyl(dimethyl)silyl)oxy]-2,3-dimethoxy-2,3-dimethylhexahydro-1,4-benzodioxin-6(5H)-one} using lithium hexamethyldisilazide (LHMDS) at -78 degreesC gave one regioisomeric enolate. The regiocontrol is governed by the axial beta-silyloxy substituent and the resulting lithium enolate is stable towards beta-elimination at temperatures up to -40 degreesC. It was found that the axial beta-silyloxy group could be conveniently eliminated using 2.1 equiv of LHMDS at 0 degreesC for 1h and that an equatorial beta-alkoxy group was much more resistant to beta-elimination. A chiral lithium amide base was used to overturn the inherent regioselectivity of ketone deprotonation with LHMDS. (C) 2004 Elsevier Ltd. All rights reserved.