AuCl_3催化羟基苯炔基酮合成氧杂螺酮的理论研究

Study on the Synthesis of Unsaturated Carbonyl-oxaspiro via Gold(Ⅲ)-catalyzed Isomerization of 2-hydroxy-2-(phenylethynyl)clohexanone

用量子化学密度泛函理论(DFT)B3LYP方法在6-311++G(d,p)基组的计算水平,对AuCl3催化羟基-苯炔基酮合成不饱氧杂螺酮的反应机理进行了理论研究.研究表明,该反应最优势路径包括炔基的活化、羰基氧与炔基碳亲核环化反应、螺碳的形成、双分子间的氢转移和催化剂解离等步骤.AuCl3催化作用的本质在于,Au(Ⅲ)与炔基配位后,降低炔基反键轨道π*(C1—C2)的能级,减小炔基反键轨道π*(C1—C2)与羰基氧原子孤对电子占据轨道2p-(LP)C=O的能级差,促进羰基氧原子的孤对电子向反键轨道π*(C1—C2)转移,使羰基-炔基之间的亲核环化反应势垒下降.另外,当用氢原子替代反应底物炔基上连接的苯基时,速率控制步骤的反应势垒升高,反应活性下降.

By using the B3LYP method of density functional theory（DFT） with 6-311＋q-G（d,p） basis set,the synthesis mechanism of unsaturated carbonyl-oxaspiro via AuC13-catalyzed 2-hydroxy-2-（ethynyl） cyclohexanone was studied. The results suggest that the overall reaction of the most favorable channel includes five steps：activation of the ethynyl,nucleophilic cyclization reaction between carbonyl-oxygen and ethynyl-carbon,formation of the spiro-carbon, intermolecular hydrogen transfer, and regeneration of the catalyst. The catalysis key of AuCI3 is that its coordination with the ethynyl decreases the anti-bonding orbital energy of the π（c1-c2） and the orbital energy-gap between π（c1-c2） and 2p-（LP）c=o ,which promotes the electron transfer from LP-（2p）c=o orbital to π（c1-c2）; orbital,and decreases the forward reaction energy barrier of the nucleophilic cyclization between carbonyl-oxygen and ethynyl-carbon. Moreover, this study indicates that while the phenyl group connected the ethynyl is replaced by hydrogen atom, the forward reaction energy barrier of rate-controlling step increases and the overall reactivity decreases.