150668-46-5Relevant academic research and scientific papers
Precise Control of the Formation of a Covalent and an Ionic Bond in Carbocation-Carbanion Combination Reactions
Takeuchi, Ken'ichi,Kitagawa, Toshikazu,Miyabo, Atsushi,Hori, Hideshi,Komatsu, Koichi
, p. 5802 - 5810 (2007/10/02)
The electronic effect on the selectivity of covalent or ionic bond formation was examined for the reaction of Kuhn's anion 1(1-) (C67H39(1-); tris(7H-dibenzofluorenylidenemethyl)methide ion) and 1-aryl-2,3-dicyclopropylcyclopropenylium ions.The carbocation stability was progressively changed by varying the substituent on the phenyl ring, while the steric effect was kept essentially unchanged.The cations having the p-chlorophenyl (2a(1+)), phenyl (2b(1+)), m-methylphenyl (2c(1+)), or m,m'-dimethylphenyl (2d(1+)) group gave a covalent product, whereas a carbocation-carbanion salt was obtained from the cations having the p-methylphenyl (2e(1+)) or p-methoxyphenyl (2f(1+)) group.The reduction potentials Ered of the cations, as determined by cyclic voltammetry, showed that the formation of the covalent or ionic product is switched by a small difference in stability ( 0.4 kcal/mol) between 2d(1+) and 2e(1+).In chloroform, the salts 1(1-)2e(1+) and 1(1-)2f(1+) were transformed into covalent forms 1-2e and 1-2f, which can exist only in solution.When 1-(2a-d) and 1(1-)2e,f(1+) were dissolved in DMSO, equilibrium between a covalent compound and ions was established.A plot of the free energy of heterolysis ΔG0het for 1-(2a-f) against the Ered of the corresponding cations 2a-f(1+) showed that ΔG0het decreases as the cation is more stabilized.The heterolysis in DMSO was shown to be enhanced by ca. 13 kcal/mol both by the steric congestion in the covalent molecules and the stabilization of the cyclopropenylium ions by solvation.
Vinylcations, 39. Zinc Chloride Catalysed Addition of Hydrogen Chloride to Cyclopropylalkynes
Hanack, Michael,Weber, Erhard
, p. 777 - 797 (2007/10/02)
Zinc chloride catalysed addition of hydrogen chloride to 1-cyclopropylalkynes 5a-e (R = CH3, c-C3H5, phenyl, p-tolyl, 4-methoxyphenyl) is studied and the results are compared with those of the addition of HCl/ZnCl2 to several substituted arylalkynes 10a-h.Thus, the alkynes are reacted with HCl/ZnCl2 in dichloromethane and the reaction products are investigated also with respect to their stereochemistry.All alkynes yield predominantly the direkt hydrogen chloride addition products.The 1-cyclopropylalkynes 5a-d give (E)-1-chloro-1-cyclopropyl-1-alkenes 15, and (E)-1-chloro-2-cyclopropyl-1-(4-methoxyphenyl)ethene (16e) is obtained as the major product from 5e (R = 4-CH3OC6H4).Moreover, ring opening to homoallenyl chlorides 19 and, as a side reaction, formation of the ketones 17 and 18 by the addition of water are observed.In a secondary addition reaction, the dichlorides 20 are also obtained by homoallyl rearrangement.The arylalkynes 10a-g react preferentially with formation of (E)-1-aryl-1-chloroalkenes 21.Relative rates are obtained by inter- and intramolecular competition reactions of the alkynes 23 and 5b-e with HCl/ZnCl2 showing the order of stabilization by substituents of the intermediate vinyl cation 2 to be 4-ClC6H4 E2 mechanism.The preferential formation of the addition products E-15, E-16, and E-21 is attributed to a syn-vinyl cation ion pair and to steric approach control of the β-substituents in the vinyl cation intermediate 2.
