Mechanism and stereoselectivity of the Rh(ii)-catalyzed cyclopropanation of diazooxindole: a density functional theory studyElectronic supplementary information (ESI) available: Comparison of different DFT methods (Table S1), calculated relative free energies with and without BSSE correction (Table S2), NBO analysis of TS11a and TS11b (Table S3), natural charge analysis (Tables S4 and S5), energy profile for the uncatalyzed cyclopropanation in Re-face pathway (Fig. S1), comparison between the DF

• Main Authors: Xue, Yun-Sheng, Cai, Yu-Ping, Chen, Zhao-Xu
• Format: Article
• Language: English
• ISSN: 2046-2069
• DOI: 10.1039/c5ra07981k

The mechanism and origin of stereoselectivity of rhodium( ii )-catalyzed cyclopropanation reactions with diazooxindole and styrene has been studied using density functional theory calculations. The catalyzed reactions by achiral Rh 2 (OAc) 4 and chiral Rh 2 ( S -PTTL) 4 as well as the uncatalyzed model were comparatively studied. The computational results indicate that the cyclopropanation step in both Rh 2 (OAc) 4 and Rh 2 ( S -PTTL) 4 models is a single concerted but asynchronous process. The nitrogen extrusion step is found to be the rate-limiting step of the catalytic cycle, whereas the cyclopropanation step is the stereoselectivity-determining step. The diastereomeric ratios (dr) and the enantiomeric excess (ee) values are successfully predicted, which are in good agreement with the experimental values. The high trans -diastereoselectivity might be governed by the π-π interactions between the syn indole ring in carbenoid ligand and the phenyl group in styrene, whereas the good enantioselectivity can be ascribed to the steric interaction between the phenyl ring in styrene and the phthalimido group in the catalyst as well as the aromatic interactions (π-π and CH-π) in the transition states. Additionally, the methodological study using different functionals demonstrated the importance of considering the dispersion interactions in the current reaction systems. This theoretical study will help in understanding the mechanism of the asymmetric cyclopropanations of olefins through carbene-transfer reactions. A density functional theory study was performed to understand the detailed mechanisms and stereoselectivity of the rhodium( ii )-catalyzed cyclopropanation reactions with diazooxindole and styrene.