铱催化(5+2)环加成一步合成七元环的计算预测

2013年,许秀芳、Houk和唐卫平课题组合作报道了Rh(PPh3)3Cl催化3-酰氧基-1,4-烯炔(ACE)和炔烃的(5+2)环加成形成环庚三烯的反应机理,他们的研究表明该机理包括1,2-羧基迁移、炔烃插入、还原消除等一系列步骤,其中1,2-羧基迁移是决定反应速率的步骤.本文利用密度泛函理论(DFT)计算预测了将价格相对便宜的Ir(PPh3)3Cl催化剂应用于ACE和炔烃分子间(5+2)环加成反应制备七元碳环的可行性.计算结果表明,利用Ir(PPh3)3Cl催化剂合成七元碳环是一种方便、高效、实用的方法,且改变催化剂并不改变反应的机理和区域选择性,而是改变了反应的决速步.

Computational prediction of one-step synthesis of seven-membered rings by (5+2) cycloaddition utilizing iridium catalyst

The mechanism of Rh(PPh3)3 Cl-catalyzed(5+2) cycloadditions of 3-acyloxy-1,4-enyne(ACE) and alkynes had been reported by Xu, Houk and Tang et al. in 2013. Their investigation revealed that the mechanism involved sequential steps of 1,2-acyloxy migration, alkyne insertion, and reductive elimination to form the cycloheptatriene product, and 1,2-acyloxy migration was found to be the rate-determining step. Herein, we used density functional theory(DFT) calculations to predict the plausibility of applying the relatively cheaper Ir(PPh3)3 Cl catalyst to the intermolecular(5+2) cycloadditions of 3-acyloxy-1,4-enyne and alkynes to produce seven-membered carbocycles. The calculation results suggest a convenient and energetically practical approach to synthesize seven-membered carbocycle using the Ir-(PPh3)3 Cl catalyst. In addition, the calculation results suggest that altering the catalyst does not change the mechanism of the reaction and preferences for the regioisomeric products, but does change the rate-determining step.