Experimental and Theoretical Exploration of the Kinetics and Thermodynamics of the Nucleophile-Induced Fragmentation of Ylidenenorbornadiene Carboxylates
作者:Abigail D. Richardson、Scott J. L’Heureux、Ava M. Henry、Elizabeth A. McDonough、Cameron J. Fleischer、Cameron C. McMullen、Trevor R. Reynafarje、Gisele P. Guerrero、Quinn E. Williams、Qingyang Zhou、David M. Malouf、Spencer E. Thurman、Julia E. Soeller、Jerry Y. Sheng、Erica A. Medhurst、Angel E. Canales、Ty B. Cecil、K. N. Houk、Philip J. Costanzo、Daniel A. Bercovici
DOI:10.1021/acs.joc.3c00980
日期:2023.8.18
calculations were performed to investigate the mechanism of fragmentation and support an asynchronous retro-[4 + 2] cycloaddition transition state. The computations generally correlated well with the observed free energies of activation for four diastereomers of the model system as a whole, within 2.6 kcal/mol. However, the observed order of the fragmentation rates across the set of diastereomers deviated from
亚叉冰片二烯 (YND) 通过富烯和乙炔羧酸盐之间的 [4 + 2] 环加成反应制备,与硫醇亲核试剂反应,根据 YND 底物的对称性产生 4 至 8 个非对映异构体的混合物。非对映异构体混合物通过逆[4 + 2]环加成发生片段化,速率变化很大,80°C 下半衰期为 16 至 11,000 分钟。丙硫醇加合物 [YND-丙硫醇 (PT)] 的非对映异构体富集样品通过核奥沃豪瑟效应光谱 (NOESY) 相关性进行分离和鉴定。使用模拟动力学从观察到的速率数据推断各个非对映异构体的速率常数,并且它与直接测量的速率常数以及从分离的非对映异构体富集样品中测量的速率常数密切相关。模型系统的各个非对映异构体以不同的速率断裂,在CDCl 3中的半衰期范围为5至44分钟。进行密度泛函理论计算来研究碎片机制并支持异步逆[4 + 2]环加成过渡态。计算结果总体上与观察到的模型系统的四种非对映异构体的活化自由能良好相关,在