Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA.
J Org Chem. 2013 Apr 19;78(8):4037-48. doi: 10.1021/jo400350v. Epub 2013 Mar 22.
The site selectivities and stereoselectivities of C-H oxidations of substituted cyclohexanes and trans-decalins by dimethyldioxirane (DMDO) were investigated computationally with quantum mechanical density functional theory (DFT). The multiconfiguration CASPT2 method was employed on model systems to establish the preferred mechanism and transition state geometry. The reaction pathway involving a rebound step is established to account for the retention of stereochemistry. The oxidation of sclareolide with dioxirane reagents is reported, including the oxidation by the in situ generated tBu-TFDO, a new dioxirane that better discriminates between C-H bonds on the basis of steric effects. The release of 1,3-diaxial strain in the transition state contributes to the site selectivity and enhanced equatorial C-H bond reactivity for tertiary C-H bonds, a result of the lowering of distortion energy. In addition to this strain release factor, steric and inductive effects contribute to the rates of C-H oxidation by dioxiranes.
采用量子力学密度泛函理论（DFT）对取代环己烷和反-十氢萘的 C-H 氧化的位点选择性和立体选择性进行了计算研究。多组态 CASPT2 方法应用于模型体系，以确定首选的反应机制和过渡态几何形状。建立了涉及回弹步骤的反应途径，以说明立体化学的保留。报告了用二氧杂环己烷试剂氧化石竹烯内酯的情况，包括用原位生成的 tBu-TFDO 进行的氧化，这是一种新的二氧杂环己烷，基于空间效应更好地区分 C-H 键。在过渡态中释放 1,3-双轴向应变有助于提高立体选择性和增强叔 C-H 键的反应活性，这是由于畸变能降低的结果。除了这种应变释放因素外，空间位阻和诱导效应也有助于二氧杂环己烷的 C-H 氧化速率。
