Wu Na, Wahl Benoit, Woodward Simon, Lewis William
School of Chemistry, University of Nottingham, University Park, Nottingham NG7 2RD (UK), Fax: (+44) 115-951-3564.
Chemistry. 2014 Jun 16;20(25):7718-24. doi: 10.1002/chem.201402394. Epub 2014 May 21.
Improved synthetic conditions allow preparation of TMSCCl3 in good yield (70%) and excellent purity. Compounds of the type NBu4X [X=Ph3SiF2 (TBAT), F (tetrabutylammonium fluoride, TBAF), OAc, Cl and Br] act as catalytic promoters for 1,4-additions to a range of cyclic and acyclic nitroalkenes, in THF at 0-25 °C, typically in moderate to excellent yields (37-95%). TBAT is the most effective promoter and bromide the least effective. Multinuclear NMR studies ((1)H, (19)F, (13)C and (29)Si) under anaerobic conditions indicate that addition of TMSCCl3 to TBAT (both 0.13 M) at -20 °C, in the absence of nitroalkene, leads immediately to mixtures of Me3SiF, Ph3SiF and NBu4CCl3. The latter is stable to at least 0 °C and does not add nitroalkene from -20 to 0 °C, even after extended periods. Nitroalkene, in the presence of TMSCCl3 (both 0.13 M at -20 °C), when treated with TBAT, leads to immediate formation of the 1,4-addition product, suggesting the reaction proceeds via a transient [Me3Si(alkene)CCl3] species, in which (alkene) indicates an Si⋅⋅⋅O coordinated nitroalkene. The anaerobic catalytic chain is propagated through the kinetic nitronate anion resulting from 1,4 CCl3(-) addition to the nitroalkene. This is demonstrated by the fact that isolated NBu4[CH2=NO2] is an efficient promoter. Use of H2C=CH(CH2)2CH=CHNO2 in air affords radical-derived bicyclic products arising from aerobic oxidation.
改进的合成条件使得能够以良好的产率（70%）和优异的纯度制备三氯甲基三甲基硅烷。NBu4X类型的化合物[X = Ph3SiF2（TBAT）、F（四丁基氟化铵，TBAF）、OAc、Cl和Br]在0至25°C的四氢呋喃中作为1,4-加成到一系列环状和非环状硝基烯烃的催化促进剂，产率通常为中等至优异（37 - 95%）。TBAT是最有效的促进剂，而溴化物效果最差。厌氧条件下的多核核磁共振研究（（1）H、（19）F、（13）C和（29）Si）表明，在-20°C下，在不存在硝基烯烃的情况下，将三氯甲基三甲基硅烷加入到TBAT（均为0.13 M）中会立即生成三甲基硅烷氟、三苯基硅烷氟和NBu4CCl3的混合物。后者在至少0°C下稳定，即使经过较长时间，在-20至0°C下也不会与硝基烯烃加成。在-20°C下，当硝基烯烃与三氯甲基三甲基硅烷（均为0.13 M）一起用TBAT处理时，会立即形成1,4-加成产物，这表明反应通过瞬态[Me3Si（烯烃）CCl3]物种进行，其中（烯烃）表示Si⋅⋅⋅O配位的硝基烯烃。厌氧催化链通过1,4 CCl3(-)加成到硝基烯烃产生的动力学硝酮阴离子进行传播。这一点通过分离得到的NBu4[CH2=NO2]是一种有效促进剂这一事实得到证明。在空气中使用H2C=CH(CH2)2CH=CHNO2会得到由有氧氧化产生的自由基衍生的双环产物。
