Effect of substituents on the competition between several mechanisms of nucleophilic vinylic substitution

Amatore, Christian; Galli, Carlo; Gentili, Patrizia; Guarnieri, Alessandra; Schottland, Ettie Z.; Rappoport, Zvi

doi:10.1039/p29950002341

Cited by 7 publications

(17 citation statements)

References 36 publications

(6 reference statements)

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“…Compound 2 , which was previously prepared and separated into E and Z isomers, , was already investigated as a stereomodel for the vinylic S N 1 reaction 3,18 under stringent conditions . It lacks vinylic or allylic C−H bonds or electron-withdrawing substituents, which can lead to substitution by elimination−addition and addition−elimination routes, respectively, , and it therefore fulfills the indicated prerequisites for being an S RN 1(V) substrate. To our surprise, the structurally similar compounds 3 (86:14 ( Z )- 3 :( E )- 3 ) and 4 (91:9 ( E )- 4 :( Z )- 4 ) did not lend themselves to the photostimulated S RN 1(V) reaction with a ketone enolate ion (see below).…”

Section: Resultsmentioning

confidence: 99%

“…The occurrence of the vinylic S RN 1 reaction (hereafter, S RN 1(V)) appears to be strongly dependent on specific structural features of the vinyl halide, which may prevent or minimize competition from alternative ionic processes (e.g., elimination−addition). So far, our investigation in this field has mainly focused on the effect of the structure of the substrate, in particular the role of certain substituents . Questions about the stereochemical course of the S RN 1(V) reaction, strictly related to the structure of the vinyl radical intermediate, were not addressed.…”

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confidence: 99%

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Stereochemistry of the Vinylic S_RN1 Reaction of Triarylvinyl Halides. The Structure of the Intermediate α-Arylvinyl Radical

et al. 1996

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Evidence for the intermediacy of a vinyl radical in the vinylic S(RN)1 reaction (S(RN)1(V)) of 2-anisyl-1,2-diphenylvinyl bromide 2 is obtained. The photostimulated S(RN)1(V) reaction of pinacolone enolate ion with (E)-2 and (Z)-2, which are used as stereoindicators, gives complete loss of the original stereochemistry of the two precursors in the substituted and hydrodehalogenated products; i.e., stereoconvergence is found. It is concluded that in the reaction of 2 a beta-substituted alpha-phenylvinyl radical is a reactive intermediate and that it has either a linear structure or an average linear structure due to a rapidly interconverting E,Z mixture of bent radicals. This conclusion is supported by comparing the stereochemical course of the S(RN)1(V) reaction with those of other reactions of the same precursor, which unambiguously give rise to the same alpha-phenylvinyl radical intermediate by alternative mechanisms. Among the reactions investigated, the hydrodehalogenation of precursor 2 by LAH appears to take place by an ET mechanism.

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Section: Resultsmentioning

confidence: 99%

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confidence: 99%

Stereochemistry of the Vinylic S_RN1 Reaction of Triarylvinyl Halides. The Structure of the Intermediate α-Arylvinyl Radical

et al. 1996

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“…Hydrodebromination of 19 with Bu 3 SnH . A solution of 50 mg of ( E )- 19 (0.25 mmol), 8 mg AIBN (0.05 mmol), and 330 μL Bu 3 SnH (1.24 mmol) in 0.6 mL benzene was irradiated 1 at 350 nm for 3 h 14b. Direct GC-MS analysis (no workup) of the reaction mixture revealed formation of fluorostyrene (retention time: 5.7 min).…”

Section: Methodsmentioning

confidence: 99%

“…These radicals were chosen in order to investigate the effect of σ-type substituents (structures 6 − 11 ) and of π-type substituents (structures 12 − 15 ) and bear some resemblance with those experimentally examined by us. , Two β-substituted vinyl radicals (structures 16 and 17 ) were also studied. The results of the calculations, carried out by using the DFT approach on these structures, are presented below.…”

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Effect of Substituents on the Structure of the Vinyl Radical: Calculations and Experiments

et al. 1997

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Literature reports indicate either a linear or a bent configuration for α-substituted vinyl radicals. In order to get a better insight into this structural question, calculations of the structure of some α-substituted vinyl radicals were conducted by the DFT approach [BLYP/6-31G(d,p) and B3LYP/6-311G(2d,2p)]. For vinyl radicals bearing σ-type substituents (Me, SH, Cl, OH, F), the bent form is found to be the minimum energy structure; the inversion barrier of the E and Z forms is found to markedly increase as the electronegativity of the group increases. Vinyl radicals bearing π-type substituents (CHCH2, CHO, CN, C6H5) are found to be linear. The effect of β-substituents is much lower, and the β-fluoro- and β-ethenylvinyl radicals, representative of σ- and π-type substituents, are calculated to be bent. Comparison with other literature calculations, obtained by different methods for some similar vinylic radicals, supports our computational results. Experimental support was also sought, with particular regards to the inversion barrier of the bent radicals. Since a very high barrier is calculated for the α-fluorovinyl radical, its inversion rate could be slower than the “sampling” time of a proper chemical reaction. Indeed, the α-fluorovinyl radicals, generated from PhCHC(F)Br by reaction with Bu3SnH/AIBN, retained the configuration of their precursors in the overall hydrodebromination process.

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“…7 The range of nucleophiles includes amines, alkoxides, sulfides, and stabilized carbanions. 3,8 Having an invariant order of nucleophilicity is not possible because different substrates and different reaction conditions affect the order of nucleophilicity. It is generally accepted that nitrogen nucleophiles such as NH 2 − , R 2 NH, and ArNH 2 have good reaction rates.…”

Section: ■ Introductionmentioning

confidence: 99%

Nucleophilic Aromatic Substitution—Addition and Identification of an Amine

et al. 2017

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The addition of a nucleophilic functional group to an electron-deficient aromatic ring is a versatile reaction in the modern organic chemistry arsenal. The proper positioning of a leaving group on this ring effectively allows for a substitution reaction to occur. A 3 h laboratory experiment is described in which students utilize a common electrophilic aromatic ring and affect a substitution with an unknown amine, the identity of which is later characterized by the melting point and 1H NMR spectrum of the product.

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Effect of substituents on the competition between several mechanisms of nucleophilic vinylic substitution

Cited by 7 publications

References 36 publications

Stereochemistry of the Vinylic S_RN1 Reaction of Triarylvinyl Halides. The Structure of the Intermediate α-Arylvinyl Radical

Stereochemistry of the Vinylic S_RN1 Reaction of Triarylvinyl Halides. The Structure of the Intermediate α-Arylvinyl Radical

Effect of Substituents on the Structure of the Vinyl Radical: Calculations and Experiments

Nucleophilic Aromatic Substitution—Addition and Identification of an Amine

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Effect of substituents on the competition between several mechanisms of nucleophilic vinylic substitution

Cited by 7 publications

References 36 publications

Stereochemistry of the Vinylic SRN1 Reaction of Triarylvinyl Halides. The Structure of the Intermediate α-Arylvinyl Radical

Stereochemistry of the Vinylic SRN1 Reaction of Triarylvinyl Halides. The Structure of the Intermediate α-Arylvinyl Radical

Effect of Substituents on the Structure of the Vinyl Radical: Calculations and Experiments

Nucleophilic Aromatic Substitution—Addition and Identification of an Amine

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Stereochemistry of the Vinylic S_RN1 Reaction of Triarylvinyl Halides. The Structure of the Intermediate α-Arylvinyl Radical

Stereochemistry of the Vinylic S_RN1 Reaction of Triarylvinyl Halides. The Structure of the Intermediate α-Arylvinyl Radical