Kinetische Studie zu Donor‐Akzeptor‐Cyclopropanen: Strukturelle und elektronische Einflüsse auf die Reaktivität

Lücht, Alexander; Kreft, Alexander; Grunenberg, Jörg; Jones, Peter G.; Werz, Daniel B.

doi:10.1002/ange.201812880

Cited by 30 publications

(1 citation statement)

References 122 publications

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“…Variation of substituents in SnCl 4 ‐catalyzed (3+2)‐cycloadditions of 2‐aryl‐1,1‐di(alkoxycarbonyl)cyclopropanes with p ‐fluorobenzaldehyde recently studied by the Werz group resulted in a linear Hammett relationship, in which EDG‐substituted substrates reacted faster than EWG‐substituted analogues. [16a] Accordingly, Werz reported that relaxed force constants calculated for the C1−C2 bonds, which undergo cleavage in the course of the reactions, correlated with the relative reaction rates: lower force constants for EDG‐substituted cyclopropanes were associated with faster reactions. We assume that complexation with the Lewis acid SnCl 4 enhanced the electron‐deficiency of the 1,1‐di(alkoxycarbonyl)‐substituted cyclopropanes such that their reactivity was entirely governed by the degree of the C−C bond polarization, consistent with the intimate ion pair mechanism suggested for this reaction by Johnson and coworkers.…”

Section: Resultsmentioning

confidence: 99%

Inherent Reactivity of Spiro‐Activated Electrophilic Cyclopropanes

Jüstel

Stan

Pignot

et al. 2021

Chemistry A European J

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The kinetics of the ring-opening reactions of thiophenolates with geminal bis(acceptor)-substituted cyclopropanes in DMSO at 20 °C was monitored by photometric methods. The determined second-order rate constants of the S N 2 reactions followed linear relationships with Mayr nucleophilicity parameters (N/s N ) and Brønsted basicities (pK aH ) of the thiophenolates as well as with Hammett substituent parameters (σ) for groups attached to the thiophenolates. Phenyl-substituted cyclopropanes reacted by up to a factor of 15 faster than their unsubstituted analogues, in accord with the known activating effect of adjacent π-systems in S N 2 reactions. Variation of the electronic properties of substituents at the phenyl groups of the cyclopropanes gave rise to parabolic Hammett relationships. Thus, the inherent S N 2 reactivity of electrophilic cyclopropanes is activated by electron-rich π-systems because of the more advanced C1À C2 bond polarization in the transition state. On the other hand, electron-poor π-systems also lower the energetic barriers for the attack of anionic nucleophiles owing to attractive electrostatic interactions.

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Section: Resultsmentioning

confidence: 99%

Inherent Reactivity of Spiro‐Activated Electrophilic Cyclopropanes

Jüstel

Stan

Pignot

et al. 2021

Chemistry A European J

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Lewis Acid‐Catalyzed Formal (4+2)‐ and (2+2+2)‐Cycloaddition Between 1‐Azadienes and Styrylmalonates as Analogues of Donor‐Acceptor Cyclopropanes

2021

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The reactions of donor‐acceptor cyclopropanes (DACs) and isomeric β‐styrylmalonates with conformationally non‐rigid α,β‐unsaturated imines in the presence of Lewis acids were studied. The effect of the structural features of starting compounds on the process course was determined. The main attention was focused to discover the reaction conditions for the formal (4+2)‐cycloaddition pathway with the possibility of variation of the α‐substituent in azadiene instead of known (3+2)‐cycloaddition synthetic methodology. Based on the results obtained, a method for the diastereoselective synthesis of substituted trans,trans‐tetrahydropyridines was developed. Three substrate‐sensitive diverse Lewis acid catalytic systems have been employed based on Sc(OTf)3, Sn(OTf)2, and GaCl3. The use of GaCl3 as a Lewis acid allows to obtain a minor product of the formal (2+2+2)‐cycloaddition, which represents a fully 1,2,3,4,5,6‐hexasubstituted cyclohexane derivative produced with diastereoselectivity >30:1. Appropriate mechanistic and stereochemical models have been suggested.

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4‐(Dimethylamino)Pyridinium Azide in Protic Ionic Liquid Media as a Stable Equivalent of Hydrazoic Acid

et al. 2022

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We report a procedure for the multigram synthesis of 4‐(dimethylamino)pyridinium azide, a stable, non‐explosive, low‐hygroscopic source of azide ion soluble in both protic and aprotic organic solvents. In protic ionic liquid media this reagent was shown to serve as a safer equivalent of toxic and unstable hydrazoic acid. The synthetic utility of this system was demonstrated using donor‐acceptor cyclopropane ring opening as a model process. General procedures furnishing a variety of dialkyl (2‐azido‐2‐arylethyl)malonates or 4‐azido‐4‐arylbutyrates, depending on the protic ionic liquid applied, were elaborated. The conversion times for studied donor‐acceptor cyclopropanes were established providing the relative reactivity sequence. The application of 4‐(dimethylamino)pyridinium azide for a conventional nucleophilic substitution, oxirane ring opening, (3+2)‐cycloaddition to (thio)cyano group as well as their combinations realized as telescopic synthesis was also demonstrated.

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Kinetische Studie zu Donor‐Akzeptor‐Cyclopropanen: Strukturelle und elektronische Einflüsse auf die Reaktivität

Cited by 30 publications

References 122 publications

Inherent Reactivity of Spiro‐Activated Electrophilic Cyclopropanes

Inherent Reactivity of Spiro‐Activated Electrophilic Cyclopropanes

Lewis Acid‐Catalyzed Formal (4+2)‐ and (2+2+2)‐Cycloaddition Between 1‐Azadienes and Styrylmalonates as Analogues of Donor‐Acceptor Cyclopropanes

4‐(Dimethylamino)Pyridinium Azide in Protic Ionic Liquid Media as a Stable Equivalent of Hydrazoic Acid

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