Department of Organic and Applied Chemistry, University of Łódź, Tamka 12, PL-91-403 Łódź, Poland.
Institute of Organic Chemistry & Technology, Cracow University of Technology, Warszawska 24, PL-31-155 Krakow, Poland.
Molecules. 2021 Sep 13;26(18):5562. doi: 10.3390/molecules26185562.
The molecular mechanisms of addition of dihalocarbenes and dimethoxycarbene to thioketones derived from 2,2,4,4-tetrmethylcyclobutane-1,3-dione were examined on the basis of the DFT wb97xd/6-311g(d,p)(PCM) calculations. Obtained results demonstrated that the examined processes exhibit polar nature and in the case of electrophilic dichloro-, and dibromocarbenes are initiated by the attack of carbene species onto the sulfur atom of the C=S group. Remarkably, reactions involving more electrophilic carbenes (dichloro-, and dibromocarbene) proceeds via stepwise mechanism involving thiocarbonyl ylide as a transient intermediate. In contrast, analogous reactions with nucleophilic dimethoxycarbene occur via a single step reaction, which can be considered as the [2 + 1] cycloaddition reaction initiated by the attack onto the C=S bond. A computational study showed that difluorocarbene tends to react as a nucleophilic species and resembles rather dimethoxycarbene and not typical dihalocarbene species. Significantly higher reactivity of the thioketone unit in comparison to the ketone group, both present in 3-thioxo-2,2,4,4-tetramthylcyclobutanone molecule, was rationalized in the light of DFT computational study.
基于 DFT wb97xd/6-311g(d,p)(PCM)计算，研究了二卤代卡宾和二甲氧基卡宾与 2,2,4,4-四甲基环丁烷-1,3-二酮衍生的硫酮的加成的分子机制。所得结果表明，所研究的过程表现出极性性质，并且在亲电二氯代和二溴代卡宾的情况下，卡宾物种攻击 C=S 基团的硫原子引发了这些过程。值得注意的是，涉及更亲电卡宾（二氯代和二溴代卡宾）的反应通过涉及硫羰叶立德作为瞬态中间体的逐步机制进行。相比之下，与亲核二甲氧基卡宾的类似反应通过单步反应进行，该反应可被视为通过攻击 C=S 键引发的[2+1]环加成反应。计算研究表明，二氟卡宾倾向于作为亲核物种反应，并且与二甲氧基卡宾而不是典型的二卤代卡宾物种更相似。在 3-硫代-2,2,4,4-四甲基环丁烷-1,3-二酮分子中存在的硫酮单元与酮基团相比表现出更高的反应性，这在 DFT 计算研究中得到了合理化。
