| C-H bond functionalization is a powerful method in organic synthesis, since it avoids prefunctionalization of substrates to introduce desired functionality. However, differentiating between numerous C-H bonds and effecting site specific and stereoselective chemical modifications is an ongoing challenge. In the first part of thesis, I will focus on the applications of quantum mechanical calculations to study C-H activations by organic and metallic reagents. Dimethyldioxirane (DMDO) is a non-metal C-H oxidation reagent. In Chapter 1, site selectivities and reactivities in C-H activations by DMDO were studied in substituted cyclohexanes and trans-decalins, which are models of natural steroids. It is found that the release of 1,3-diaxial strain in the transition state contributes to the site selectivities and enhanced equatorial C-H bond reactivities for tertiary C-H bonds. In Chapter 2, C-H activation reactions that occur with the Grubbs metathesis catalyst were found to be controlled by closed-shell repulsions between the groups that chelate the ruthenium metal.;In the second part of the thesis, quantum mechanical computations with density functional theory (DFT) are employed to investigate the stereoselectivities and reactivities in the reactions. In Chapter 3, the origins of asymmetric conjugative addition of arylboronic acid to beta-substituted enone. In Chapter 4, I have demonstrated the hyperconjugative aromaticity of 5-substituted cyclopentadienes and its effect on the pi-facial selectivity in Diels-Alder cycloadditions. |
