From QCA (Quantum Cellular Automata) to Organocatalytic Reactions with Stabilized Carbenium Ions

Gualandi, Andrea; Mengozzi, Luca; Manoni, Elisabetta; Cozzi, Pier Giorgio

doi:10.1002/tcr.201500299

Cited by 11 publications

(4 citation statements)

References 155 publications

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“…7d,8 However, the advantages provided by the Mayr−Patz reactivity scale from an experimental perspective are unquestionable. 9 Given N, s N , and E for two reaction partners, it is possible to predict semiquantitatively their reaction rate constant k at 20 °C. Moreover, comparison of N for different nucleophiles (or E for different electrophiles) gives direct evaluation of their relative reactivity.…”

Section: ■ Introductionmentioning

confidence: 99%

Nucleophilicity Prediction via Multivariate Linear Regression Analysis

2021

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The concept of nucleophilicity is at the basis of most transformations in chemistry. Understanding and predicting the relative reactivity of different nucleophiles is therefore of paramount importance. Mayr’s nucleophilicity scale likely represents the most complete collection of reactivity data, which currently includes over 1200 nucleophiles. Several attempts have been made to theoretically predict Mayr’s nucleophilicity parameters N based on calculation of molecular properties, but a general model accounting for different classes of nucleophiles could not be obtained so far. We herein show that multivariate linear regression analysis is a suitable tool for obtaining a simple model predicting N for virtually any class of nucleophiles in different solvents for a set of 341 data points. The key descriptors of the model were found to account for the proton affinity, solvation energies, and sterics.

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Section: ■ Introductionmentioning

confidence: 99%

Nucleophilicity Prediction via Multivariate Linear Regression Analysis

2021

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“…How was it then possible that MacMillan catalysts were successfully used for asymmetric alkylations of aldehydes by preformed carbocations and by S N 1-type reactions with alcohols? The reversibility of the attack of imidazolidinones at carbocations with E < −3 observed in this work (cf. Figures and ) indicates the underlying reason: Even if the imidazolidinone catalyst is partially consumed by the addition to the S N 1 substrate, this reaction is reversible, and retroaddition takes the catalyst and the electrophile back to the productive organocatalytic cycle, in which the corresponding enamine undergoes an irreversible reaction with the electrophilic substrate.…”

Section: Discussionmentioning

confidence: 73%

Basicities and Nucleophilicities of Pyrrolidines and Imidazolidinones Used as Organocatalysts

Maji

Min

et al. 2020

J. Am. Chem. Soc.

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The Brønsted basicities pK aH (i.e., pK a of the conjugate acids) of 32 pyrrolidines and imidazolidinones, commonly used in organocatalytic reactions, have been determined photometrically in acetonitrile solution using CH acids as indicators. Most investigated pyrrolidines have basicities in the range 16 < pK aH < 20, while imidazolidinones are significantly less basic (10 < pK aH < 12). 2-(Trifluoromethyl)pyrrolidine (A14, pK aH 12.6) and the 2-imidazoliummethyl-substituted pyrrolidine A21 (pK aH 11.1) are outside the typical range for pyrrolidines with basicities comparable to those of imidazolidinones. Kinetics of the reactions of these 32 organocatalysts with benzhydrylium ions (Ar2CH+) and structurally related quinone methides, common reference electrophiles for quantifying nucleophilic reactivities, have been measured photometrically. Most reactions followed second-order kinetics, first order in amine and first order in electrophile. More complex kinetics were observed for the reactions of imidazolidinones and several pyrrolidines carrying bulky 2-substituents, due to reversibility of the initial attack of the amines at the electrophiles followed by rate-determining deprotonation of the intermediate ammonium ions. In the presence of 2,4,6-collidine or 2,6-di-tert-butyl-4-methyl-pyridine, the deprotonation of the initial adducts became faster, which allowed the rate of the attack of the amines at the electrophiles to be determined. The resulting second-order rate constants k 2 followed the correlation log k 2(20 °C) = s N(N + E), where electrophiles are characterized by one parameter (E) and nucleophiles are characterized by the two solvent-dependent parameters N and s N. In this way, the organocatalysts A1–A32 were integrated in our comprehensive nucleophilicity scale, which compares n-, π-, and σ-nucleophiles. The nucleophilic reactivities of the title compounds correlate only poorly with their Brønsted basicities.

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“…This can be rationalized by the stabilization effect of the heteroatom towards the generated carbocation intermediate, enabling the cross coupling under oxidative conditions. [99][100][101][102] Consequently, the asymmetric version of sp 3 C-H/sp 3 C-H CDC has been widely studied and a variety of successful reactions have been developed. asymmetric synthesis.…”

Section: Organocatalytic Enantioselective Sp 3 C-h/sp 3 C-h Cdc React...mentioning

confidence: 99%