Computational Study on Mechanisms and Origins of Selectivities in Rh(I)-Catalyzed Cycloisomerizations of 1,6-Allenynes with Tethered Unsaturated Carbon–Carbon Bonds

Abstract

Rhodium­(I)-catalyzed cycloisomerization reactions of 1,6-allenynes with a tethered alkene (homoallylallene–alkyne substrate) or alkyne (homopropargylallene–alkyne substrate) have recently shown great potential in the construction of polycyclic skeletons. To understand the influence of the tethered unsaturated carbon–carbon bond on cycloisomerization mechanisms, density functional theory (DFT) calculations have been performed in this work. Our calculations indicate that both cycloisomerizations involve oxidative cyclization and migratory insertion but the distinct regioselectivity between alkene and alkyne insertions and the contrasting reactivity of rhodium-alkyl and rhodium-alkenyl intermediates contribute to the divergent cycloisomerization mechanisms. In the case of alkene-tethered 1,6-allenyne, both 1,2- and 2,1-insertions of alkene into the Rh–C­(sp2) bond of the five-membered rhodacyclic intermediate are plausible, and the resulting rhodium-alkyl intermediates will afford cycloisomerization products through reductive elimination. In contrast, only 1,2-alkyne insertion is practical in the reaction of alkyne-tethered 1,6-allenyne, and the formed rhodium-alkenyl intermediate cannot undergo reductive elimination but rather rearranges into a reactive rhodacyclopropene, thereby releasing cyclic products through the 1,2-migration of rhodium carbene. Further distortion/interaction analysis on insertion transition states suggests that the different regioselectivity arises from the distinct features of configurational rearrangement for alkene and alkyne fragments during 1,2-migratory insertion. The computations also highlight the effects of the alkyne substituent and carbon chain length of the 1,6-allenyne reactant on the product selectivity.

Understanding the Nonlinear Hammett Relationship in Osmylation of Olefins with OsO4–Amine Ligands: Importance of Singlet-Diradical Character

“…The distortion/interaction activation energy decomposition scheme has garnered great attention and has been widely applied to understanding reactivity, regioselectivity, and stereoselectivity. − We applied the scheme to analyze the current calculation results. Shown in Figure are the distortion energy (A) and interaction energy (B) against the substituent sigma values.…”

Mechanistic insight into Cp*Rh(iii)-catalyzed Lossen rearrangement vs C–N reductive elimination for the synthesis of pyridones

“…The combination of B3LYP for geometry optimizations with the M06 functional for single-point energy calculations has been widely used to describe transition-metal catalyzed organometallic systems and proved to be highly efficient. [34][35][36] The solvent effect was considered with the SMD model 37 using tetrahydrofuran (e = 7.4257) as a solvent. Unless stated otherwise, all reported Gibbs free energies herein are the singlepoint energies in the solution phase with the Gibbs free energy corrections obtained in the gas phase.…”

Density Functional Theory Study of Gold-Catalyzed 1,2-Diarylation of Alkenes: π-Activation versus Migratory Insertion Mechanisms

“…Alternatively, paths II and III in Scheme describe the migratory insertion mode referring to previous outstanding works. − For path II, the C–C double bond of the aryl alkene inserts into the Au III –C bond in D to form intermediate G , which further undergoes C–H activation followed by reductive elimination to obtain the desirable product with the regeneration of Au I complex A . In contrast, path III consists of three elementary steps: C–H bond activation, migratory insertion, and reductive elimination.…”