Generation Of Vinyl Cations Research Articles

On the Gold-Catalyzed Generation of Vinyl Cations from 1,5-Diynes.

Conjugated 1,5-diynes bearing two aromatic units at the alkyne termini were converted in the presence of a gold catalyst. Under mild conditions, aryl-substituted dibenzopentalenes were generated. Calculations predict that aurated vinyl cations are key intermediates of the reaction. A bidirectional approach provided selective access to the angular annulated product in high yield, which was explained by calculations.

The generation of vinyl cations and excited triplet states by laser flash irradiation of arylalkynes

AbstractLaser flash photolysis of 4‐methoxyphenyl (anisyl) substituted alkynes 1 in protic and aprotic solvents was investigated in order to study the generation of the α‐anisylvinyl cations 2 by laser flash photoprotonation of the arylalkynes. Cations 2 were generated in 2,2,2‐trifluoroethanol, but the excited triplet state of arylalkyne 1 was detected in the aprotic solvents dichloromethane and acetonitrile. Reaction of the cations 2 with sodium azide was investigated and found to be diffusion controlled; reactions of 2 with cyclohexa‐1,3‐diene were also investigated and found to be appreciably affected by steric hindrance due to the β‐substituents. Copyright © 2002 John Wiley & Sons, Ltd.

Vinyl carbocations: solution studies of alkenyl(aryl)iodonium triflate fragmentations.

Generation of vinyl cations is facile by fragmentation of alkenyl(aryl)iodonium trifluoromethanesulfonates. Kinetics and electronic effects were probed by (1)H NMR spectroscopy in CDCl(3). Products of fragmentation include six enol triflate isomers in addition to iodoarenes. The enol triflates arise from direct reaction of a triflate anion with the starting iodonium salts as well as triflate reaction with rearranged secondary cations derived from those salts. G2 calculations of the theoretical isodesmic hydride-transfer reaction between secondary vinyl cation 7 and primary vinyl cation 6 reveal that cation 6 is 17.8 kcal/mol higher in energy. Activation parameters for fragmentation of (Z)-2-ethyl-1-hexenyl(3,5-bis-trifluoromethylphenyl)iodonium triflate, 17e, were calculated using the Arrhenius equation: E(a) = 26.8 kcal/mol, Delta H(++) = 26.2 kcal/mol, and Delta S(++) = 11.9 cal/mol x K. Added triflate increases the rate of fragmentation slightly, and it is likely that for most beta,beta-dialkyl- substituted vinylic iodonium triflates enol triflate fragmentation products are derived from three competing mechanisms: (a) vinylic S(N)()2 substitution; (b) ligand coupling (LC); and (c) concerted aryliodonio departure and 1,2-alkyl shift leading to secondary rather than primary vinyl cations.

ChemInform Abstract: Generation of Vinyl Cations by Addition to Acetylenes and Allenes

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Generation of vinyl cations by nitrosation of N‐silylated imines and enamines

AbstractThe reaction of monosilylated imines and a disilylated enamine with nitrosyl salts in dichloromethane at −78°C is shown to proceed via intermediate vinyl diazonium salts and vinyl cations.

Photochemistry of organic halides: Some interesting features of the photobehaviour of vinyl halides and vinylidine dihalides derived from camphene

A study of the photochemistry of vinylidine dihalides 1 and 2 and vinylhalides 4 and 5 revealed some interesting differences in their photobehaviour. This study led to uncover an important constraint in the generation of vinyl cations from certain α-unsubstituted vinyl halides such as 4 .

The generation of vinyl cations by beckmann fragmentation of α,β-unsaturated ketoxime derivatives

The generation of vinyl cations by beckmann fragmentation of α,β-unsaturated ketoxime derivatives

ChemInform Abstract: GENERATION OF VINYL CATIONS BY SOLVOLYSIS REACTIONS, A LESSER KNOWN GENRE OF CARBENIUM IONS

Considers the structure and geometry of vinyl cations; modes of generation of vinyl cations; heterolysis of vinyl substrates; and mechanisms of solvolysis of vinyl substrates.

The Generation of Vinyl Cations from Vinyltriazenes

The Generation of Vinyl Cations from Vinyltriazenes