ARC Centre of Excellence for Free-Radical Chemistry and Biotechnology, Research School of Chemistry, Australian National University, Canberra, ACT, Australia.
J Org Chem. 2013 Jul 5;78(13):6677-87. doi: 10.1021/jo400927y. Epub 2013 Jun 24.
The utility of chloroform as both a solvent and a hydrogen atom donor in Barton reductive decarboxylation of a range of carboxylic acids was recently demonstrated (Ko, E. J. et al. Org. Lett. 2011, 13, 1944). In the present work, a combination of electronic structure calculations, direct dynamics calculations, and experimental studies was carried out to investigate how chloroform acts as a hydrogen atom donor in Barton reductive decarboxylations and to determine the scope of this process. The results from this study show that hydrogen atom transfer from chloroform occurs directly under kinetic control and is aided by a combination of polar effects and quantum mechanical tunneling. Chloroform acts as an effective hydrogen atom donor for primary, secondary, and tertiary alkyl radicals, although significant chlorination was also observed with unstrained tertiary carboxylic acids.
最近有人证明氯仿既可用作溶剂，也可用作 Barton 还原脱羧反应中一系列羧酸的氢原子供体（Ko，E. J. 等人，Org. Lett. 2011，13，1944）。在本工作中，通过电子结构计算、直接动力学计算和实验研究的结合，研究了氯仿在 Barton 还原脱羧反应中作为氢原子供体的作用，并确定了该过程的适用范围。研究结果表明，氯仿中的氢原子直接发生转移，受动力学控制，这一过程受到极性效应和量子力学隧道效应的共同作用。氯仿可作为伯、仲和叔烷基自由基的有效氢原子供体，尽管未被张力束缚的叔羧酸也会发生显著的氯化。
