Use of Aromatic Radical-Anions in the Absence of THF. Tandem Formation and Cyclization of Benzyllithiums Derived from the Attack of Homo- and Bishomoallyllithiums on α-Methylstyrenes: Two-Pot Synthesis of Cuparene<sup>1</sup>
作者:Theodore Cohen、Thanapong Kreethadumrongdat、Xiaojun Liu、Vithalanand Kulkarni
DOI:10.1021/ja004353+
日期:2001.4.1
developed. The radical anion can be generated and the reductive lithiation performed in dimethyl ether at -70 degrees C. After the addition of diethyl ether or other solvent, and evaporation of the dimethyl ether in vacuo, the alpha-methylstyrene is added and the solution is warmed to -30 degrees C. When the unsaturated alkyllithium is primary, no adduct forms in THF due to polymerization of the alpha-methylstyrene
当通过自由基阴离子锂 1-(二甲基氨基)萘基 (LDMAN) 将相应苯基硫醚还原锂化而生成的均或双烯丙基锂添加到 α-甲基苯乙烯时,串联加成/环化为苯基取代的五-或六元环发生。α-甲基苯乙烯的聚合会影响产率,该过程受到四氢呋喃 (THF) 的青睐,四氢呋喃 (THF) 是用于生成芳族锂自由基阴离子的溶剂。因此,开发了一种在不存在 THF 的情况下生成 LDMAN(对其他常见自由基阴离子不成功)的新方法。可生成自由基阴离子,在-70℃二甲醚中进行还原锂化。加入乙醚或其他溶剂,真空蒸发二甲醚后,加入α-甲基苯乙烯并将溶液加热至-30°C。当不饱和烷基锂是伯时,由于α-甲基苯乙烯的聚合,在THF中没有形成加合物,但在主要包含己烷的溶剂中获得中等产率。还发现即使在环境温度下,在 THF 存在下会质子化的环化有机锂也可以被亲电子试剂捕获。报道了使用该技术以 46% 的产率合成倍半萜烯 (+/-)-cuparene