Dynamic Refolding of Ion-Pair Catalysts in Response to Different Anions

Abstract

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Insight into the Folding and Cooperative Multi‐Recognition Mechanism in Supramolecular Anion‐Binding Catalysis

“…[5,14] We began our investigation by exploring the possible dimerizationo ra ggregation of 1 in solution by studyingn onlineare ffects [15] in the model asymmetric Reissert reaction of quinoline with isopropyl tert-butyldimethylsilylketene acetal( Figure2). [5] Differing from the recent studies with thiourea catalysts that showeda na ctivation/deactivation mechanism, [16] 1 showedc lose to a1 :1 relationship between the ee of the catalyst and the ee of the resultant product, which suggests that this type of catalysts stays primarily monomeric during the reaction course.…”

Progress in (Thio)urea‐ and Squaramide‐Based Brønsted Base Catalysts with Multiple H‐Bond Donors

“…[85,86] along with model DFT calculations of both the catalyst alone and ion paired to anions were insightful. [88] In its native form, the catalyst folds through intramolecular H-bonds between the urea and thiourea units. This folding is maintained intact when forming catalytically relevant salts with larger anions that mimic the dialkyl malonate substrates.…”

“…Pihko, 2012, 2019. [87,88] Scheme 47. Asymmetric reaction between nitroalkanes and aromatic aldehydes catalyzed by C2-symmetric bis-thiourea BBs.…”

Non-Covalent Interactions in Enantioselective Organocatalysis: Theoretical and Mechanistic Studies of Reactions Mediated by Dual H-Bond Donors, Bifunctional Squaramides, Thioureas and Related Catalysts

“…Other studies have been performed on this reaction and other bifunctional thiourea-based organocatalyzed Michael additions since then, but only the more recent literature is reviewed here. NMR, crystallographic, and computational studies on related systems have revealed that in the lowest energy-binding conformation, the catalyst displays a "syn, anti" configuration of the thiourea functional group and not the traditional thiourea "anti, anti" configuration shown in Figure 4a [20][21][22][23]. Generally, there are three main activation modes possible to explain thiourea-tertiary amine organocatalysis, namely mode A, attributed to Takemoto et al [17], mode B, attributed to Pápai et al [19] and mode C, attributed to Wang et al [24] (Figure 4b).…”

“…The reaction mechanism was investigated, and it was observed that there were no nonlinear effects, which suggested that the rate-limiting step involves only one catalyst unit. The nature of the transition state of the rate-and stereo-determining step, the Mannich addition for the reaction between 63 and N-phenyl benzimine catalyzed by C29 was investigated using B3LYP-GD3[22]/6-311+G** PCM [23] (diethyl ether)//B3LYP/6-31G* calculations as implemented by Gaussian 09. The lowestenergy transition structures found leading to the major and minor enantiomers of the product are shown in Figure 37.…”