Computational study on the mechanism and enantioselectivity of Rh₂(S-PTAD)₄catalyzed asymmetric [4+3] cycloaddition between vinylcarbenoids and dienes

Abstract

In this paper, the mechanism of chiral rhodium-catalyzed [4+3] cycloaddition between a vinylcarbenoid and a diene to form cycloheptadiene has been studied using a two-layer ONIOM methodology consisting of density functional theory and semiempirical PM6. The mechanism involves the formation of vinylcarbenoid via nitrogen extrusion, cyclopropanation to form a divinylcyclopropane through removal of the catalyst, followed by Cope rearrangement of the resulting cisdivinylcyclopropane to form a cycloheptadiene. In this study calculations were carried out on tandem reactions of vinyldiazoacetate and siloxyvinyldiazoacetate with the consideration of geometric isomerism. Through the analysis of thermodynamics and kinetics the Cope rearrangement involving a boat transition state was determined as the rate-controlling step. The computational results indicated that siloxy substituted vinylcarbenoid displays a higher energy barrier and obtains reasonably higher enantioselectivity than for cyclopropanation of unsubstituted vinylcarbenoid, thus it has a critical influence on the favored product of ring extension and the chemical activity. Besides, the geometric isomerism of the substrates and the trapping approach were predicted to have full control over the stereogenic center of the final product rather than the enantioselectivity. Moreover, a desired relationship between the properties of the substrates and reaction energies has been established to understand the reactivity trend by activation strain model (ASM). Finally, an energy span model and AUTOF program were used to create a link between the catalytic cycles and the properties of the substrates. Fig. 5 Structural views of the transition states for the cycloaddition reaction of vinyldiazoacetate 2a-II and siloxydiazoacetate 2b-II with trapping agent 6-II, catalyzed by Rh 2 (S-PTAD) 4 . 83466 | RSC Adv., 2015, 5, 83459-83470 This journal is

Computational chemical analysis of Ru(II)‐Pheox–catalyzed highly enantioselective intramolecular cyclopropanation reactions

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Constructing Bridges between Computational Tools in Heterogeneous and Homogeneous Catalysis

“…Similarly, Wang et al referred to the calculation of X TOF and δE to rationalize the activity and the enantioselectivity of [4 + 3] cycloaddition between vinylcarbenoids and dienes catalyzed by rhodium complexes . Using ESM, they not only identified TDI and TDTS in a complex mechanistic scenario, but they also rationalized the effect of substitution on the X TOF of the different species and, consequently, on the stereoselectivity of the reaction.…”

Computational Studies on the Mechanism of Rh‐Catalyzed Decarbonylative [5+2–1] Reaction between Isatins and Alkynes: High Selectivity by Directing Group

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