Reactivity of Di-tert-butyl-oxiranyllith­ium - An Ab Initio Study

• Published in: European journal of organic chemistry 2014-02, Vol.2014 (4), p.810-817
• Main Authors: Hadjadj-Aoul, Ratiba, Bouyacoub, Abdelatif, Volatron, François
• Format: Article
• Language: English
• Subjects: Ab initio calculations; Anions; Lithiation; Reaction mechanisms; Small ring systems
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201301066

The reactivity of di‐tert‐butyl‐oxiranyllithium has been studied by means of ab initio calculations at the MP2 and CCSD(T)//MP2 levels of calculation. Six reaction pathways have been studied: three ring‐opening reactions, two cyclopropanation reactions, and addition to an alkyllithium. In each case, extrema and transition states have been located and characterized at the MP2 level. For all reactions under study, effects of the solvation by one or two additional alkyllithium molecules have been considered. It is found that the cyclopropanation reactions and one ring‐opening reaction are the most favorable pathways, which is in agreement with the experimental data. A comparison with the reactivity of mono‐tert‐butyl‐oxiranyllithium (previously studied at the same level of calculations) is presented. The origin of the different reactivities of these two species mainly comes from steric effects, which are more important in the di‐tert‐butyl‐substituted compound. Finally cyclobutanation reactions have been studied for both species. This reaction could be competitive only in the case of the di‐tert‐butyl species. According to our high‐level ab initio calculations, di‐tert‐butyl‐oxiranyllithiumoxiranyl lithium preferentially undergoes a cyclopropanation reaction, in agreement with the experimental observations. Addition of RLi followed by Li2O elimination is shown to be disfavored although it is the preferred pathway in the case of mono‐tert‐butyl‐oxiranyllithium.