Lewis acid-promoted Kharasch-Curran additions: a competition kinetics study of bromine atom transfer addition of N-alpha-bromoacetyl-oxazolidinone to 1-hexene.
Lewis acid-promoted Kharasch-Curran additions: a competition kinetics study of bromine atom transfer addition of N-alpha-bromoacetyl-oxazolidinone to 1-hexene.
复制标题
路易斯酸促进的 Kharasch-Curran 加成：N-α-溴乙酰基-恶唑烷酮与 1-己烯的溴原子转移加成的竞争动力学研究。
DOI：
10.1021/jo0201676
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
Porter,NedA
中科院分区：
文献类型：
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作者：
Feng,Hao;Kavrakova,IvankaK;Pratt,DerekA;Tellinghuisen,Joel;Porter,NedA
Lewis酸能有效地促进α-溴乙酸衍生的恶唑烷酮亚胺底物1的自由基原子转移反应。因此，在1,2-二氯乙烷或1/9 THF/二氯乙烷的共溶剂混合物中，在钪或三酸钇的存在下，1 -己烯发生自由基链加成，得到原子转移加成化合物6。在1,2-二氯乙烷中，溶液是不均匀的，而助溶剂混合物即使在- 78°C的温度下也能得到均匀的溶液。在加入四氯化碳的两种溶剂体系中进行竞争实验，研究Lewis酸对产物分布的影响。在四氯化碳存在的情况下，除了生成氯化物外，还生成氯化物，这两种产物的比例取决于存在的路易斯酸的量。在有三酸钇存在的助溶剂体系中，溴原子转移的反应速率比未添加路易斯酸时提高了400倍。在溶剂1,2-二氯乙烷中也获得了显著的速率提高，尽管该体系的分析由于介质的非均相性质而变得复杂。对配合和未配合的恶唑烷酮溴化物的C - Br键离解能（BDE）的计算表明，由于强吸电子基团对C - Br键偶极子的影响，配合降低了BDE。
Lewis acids can efficiently promote free radical atom transfer reactions of an oxazolidinone imide substrate,1, derived from α-bromo acetic acid. Thus,1undergoes a radical chain addition to 1-hexene giving the atom transfer addition compound,6, in the presence of scandium or ytterbium triflate in 1,2-dichloroethane or a cosolvent mixture of 1/9 THF/dichloromethane. In 1,2-dichloroethane the solution is heterogeneous, while the cosolvent mixture gives a homogeneous solution, even at temperatures of −78 °C. Competition experiments were carried out in both solvent systems with added carbon tetrachloride to study how Lewis acid affected the product distribution. In the presence of carbon tetrachloride, chloride7is formed in addition to6and the ratio of these two products depends on the amount of Lewis acid present. In the presence of ytterbium triflate, in the cosolvent system, the reaction rate of bromine atom transfer was enhanced up to 400-fold compared to the reaction without added Lewis acid. Significant rate enhancements were also obtained in the solvent 1,2-dichloroethane, although the analysis of the system is complicated by the heterogeneous nature of the medium. Computation of C−Br bond dissociation energies (BDE) of the complexed and uncomplexed oxazolidinone bromide suggest that complexation lowers the BDE due to the effect of the strong electron-withdrawing group on the C−Br bond dipole.