Mechanistic competition variations due to the substituents in the lithium carbenold promoted cyclopropanation reactions

作者：Zhou, Yu Bing^*; Cao, Feng Lei

来源：Journal of Organometallic Chemistry, 2007, 692(17): 3723-3731.

DOI：10.1016/j.jorganchem.2007.05.014

• cyclopropanation
• lithium carbenoid
• methylene transfer
• carbometalation
• density functional theory

The cyclopropanation reactions of the LiCH2X (X = F, Cl, Br and I) carbenoids with ethylene were investigated at the CCSD(T)/6-311 GB3LYP/6-311G** level of theory along two reaction pathways: methylene transfer and carbometalation. There exists a competition between these two reaction pathways for the different substituted lithium carbenoids. Interestingly, the substituent has different effect on the methylene transfer and carbometalation pathways. The trend of the activation energies for the methylene transfer pathway is LiCH2F (9.8 kcal/mol) > LiCH2Cl (7.6 kcal/mol) approximate to LiCH2Br (7.4 kcal/mol) approximate to LiCH2I (7.5 kcal/mol), whereas the activation energies for the carbometalation pathway increases in this order: LiCH2F (6.1 kcal/mol) < LiCH2Cl (7.1 kcal/mol) < LiCH2Br (8.2 kcal/mol) < LiCH2I (8.5 kcal/mol). The different effect mainly arises from that the substituent of the lithium carbenoid influences the hybridization character of the C-1 atom. The mechanistic competition varies due to the different substituents of the lithium carbenoids during the cyclopropanation reactions. This result is revelatory for us to control mechanistic competition to obtain target product by modifying the substituents of the lithium carbenoids.

• 出版日期2007-8-1
• 单位河西学院; 中山大学