Computational Study of the Substitution Effect on the Mechanism for the Gold(I)‐Catalyzed Ring Expansions of Unactivated Alkynylcyclopropanes

Abstract

The ring expansion reactions of unactivated alkynylcyclopropanes X-CºC-C 3 H 5 ® X-C=C 4 H 5 (X = H, F, Cl, Me, OMe, NMe 2 , CMe 3 ) were examined using the density functional theory calculations. All of the structures were completely optimized at the B3LYP/6-311++G** level of theory. For clarify the effect of the cationic gold(I), we also added AuPH 3 + as the catalyst into the system and the structures for Au were calculated at the B3LYP/LANL2DZ level of theory. The main finding of this work is that the singlet-triplet splitting of X-CºC-C 3 H 5 play an important role in determining the kinetic and thermodynamic stability of the unactivated ring expansion reactions. When X-CºC-C 3 H 5 with a smaller singlet-triplet splitting is utilized, the reaction has a smaller activation energy and a larger exothermicity.

Gold-Catalyzed Synthesis of Small Rings

“…A DFT study of this reactions was also carried out. 668 A heterogeneous gold(I)-catalyzed version of this transformation was developed using Fe 3 O 4 @SiO 2 −PPh 2 −AuOTf supported on magnetic nanoparticles that could be recycled up to 10 times, maintaining a catalytic activity comparable to the previous homogeneous version. 669 3.1.2.…”

“…Aryl- and alkyl-alkynylcyclopropanes 587 were suitable substrates, whereas terminal alkynes underwent ring expansion instead. A DFT study of this reactions was also carried out …”