Substituent Effects on the Ring-Opening Mechanism of Lithium Bromocyclopropylidenoids to Allenes

Date

2008-11-07

Author

AZİZOĞLU, AKIN
Balcı, Metin
Mieusset, Jean-Luc
Brinker, Udo H.

Metadata

Show full item record

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Item Usage Stats

175
views

0
downloads

The ring-opening reactions of lithium bromocyclopropylidenoids to allenes have been investigated computationally at the B3LYP/6-31 G(d) level of theory. Formally, two pathways can be considered: the reaction may either proceed in a concerted fashion or stepwise with the intermediacy of a free cyclopropylidene. In both cases, the loss of the bromide ion determines the kinetic of the reaction. The stability of the reactive intermediate, i.e., the carbene, is dependent on the substituent. Cyclopropylidenes bearing an electron-donating group (+M) are extremely unstable and ring-open readily to the allene. In contrast, bromocyclopropylidenoids with electron-withdrawing groups are particularly stable species. Here, a high energy barrier needs to be overcome in order to split off bromide and to generate the corresponding carbene or allene. Still, for most of the monosubstituted cyclopropylidenes investigated during this Study, the activation energy for the cyclopropylidene to allene rearrangement is lower than the energy required for parent compound (X = H) except for X = -SiH3 and -CF3.

Subject Keywords

Organic Chemistry

URI

https://hdl.handle.net/11511/56622

Journal

JOURNAL OF ORGANIC CHEMISTRY

DOI

https://doi.org/10.1021/jo8011144

Collections

Graduate School of Natural and Applied Sciences, Article

Suggestions

OpenMETU
Core

Transition structures, energetics, and nucleus-independent chemical shifts for divinylcyclobutene-to-cyclooctatriene rearrangement: A DFT study Zora, Metin (American Chemical Society (ACS), 2004-02-06) The minimum energy reaction paths and nucleus-independent chemical shifts (NICS) for the Cope rearrangement of cis-3,4-divinylcyclobutene, obtained by (U)B3LYP/6-31G* calculations, are reported. Three transition structures (endo-boatlike, chairlike, and exo-boatlike) have been located, giving rise to formation of cis,cis,cis-, cis,cis,trans-, and trans,cis, trans- 1, 3,5-cyclooctatrienes, respectively. The minimum energy path proceeds through an endo-boatlike, aromatic transition structure. The reaction pat...
Incorporation of an allene unit into alpha-pinene: Generation of the cyclic allene 2,7,7-trimethylbicyclo[4.1.]octa-2,3-diene and its dimerization Azizoglu, A; Ozen, R; Hokelek, T; Balcı, Metin (American Chemical Society (ACS), 2004-02-20) The reaction of etheral methyllithium with 3,3-dibromo-2,7,7-trimethyl-tricyclo[4.1.1.0.(2,4)] octane (2) was investigated. The generated carbene 12 undergoes intramolecular C-H insertion to provide the tetracyclic hydrocarbon 3 and the bicyclic allene 15, which undergoes [2 + 2] cyclodimerization. The structures of the formed allene dimers 16, 17, and 18 were elucidated by spectral means. The activation barriers for all possible C-H insertion products 3, 13, and 14 and the allene 15 were investigated by us...
Transition structures, energetics, and nucleus-independent chemical shifts for 6 pi electrocyclizations of dienylketenes to cyclohexadienones: A DFT study Zora, Metin (American Chemical Society (ACS), 2004-03-19) 6pi electrocyclizations of dienylketenes to 2,4-cyclohexadienones have been investigated at the (U)B3LYP/6-31G* level and found to be a favored and exothermic process for most dienylketenes. As evidenced by calculations, dienylketene cyclizations proceed via a pseudopericyclic process. If the terminal double bond of dienylketenes is embedded into a benzenoid-type aryl moiety, the partial or complete loss of aromaticity, as indicated by NICS values, increases the activation barrier and makes the reaction les...
Addition of trifluoromethyltrimethylsilane to acyl phosphonates: Synthesis of TMS-Protected 1-alkyl-1-trifluoromethyl-1-hydroxyphosphonates and 1-aryldifluoroethenyl phosphates Demir, Ayhan Sıtkı; Eymur, Serkan (American Chemical Society (ACS), 2007-10-26) Addition reactions of nucleophilic CF3TMS to acyl phosphonates were investigated. Various acyl phosphonates reacted readily with CF3TMS in the presence of K2CO3 in DMF at rt to give 1-alkyl-2,2,2-trifluoro-1-trimethylsilyloxyethylphosphonate in 70−90% yields. When benzoyl phosphonates were used as starting material, after addition of CF3, the formed alcoholate undergoes phosphonate−phosphate rearrangement to form the acyl anion, followed by elimination of F- to give 1-aryldifluoroethenyl phosphates in 87−97...
Synthesis of 1,2,3,5- tetrasubstituted pyrrole derivatives via 5-exo-dig type cyclization and stereoselective functionalisation of ferrocene derivatives Kayalar, Metin; Demir, Ayhan Sıtkı; Department of Chemistry (2005) A convenient and new method for the synthesis of 1,2,3,5-tetrasubstituted pyrrole derivatives starting from 1,3,-dicarbonyl compounds through acid catalyzed cyclization reaction is described. Alkylation of 1,3-dicarbonyl compound with propargyl bromide followed by one step cyclization with the introduction of primary amines in the presence of catalytic amount of triflouroacetic acid (TFA) affords the corresponding pyrrole derivatives in high yields. The investigations on the studies of developing a new meth...

Citation Formats

A. AZİZOĞLU, M. Balcı, J.-L. Mieusset, and U. H. Brinker, “Substituent Effects on the Ring-Opening Mechanism of Lithium Bromocyclopropylidenoids to Allenes,” JOURNAL OF ORGANIC CHEMISTRY, pp. 8182–8188, 2008, Accessed: 00, 2020. [Online]. Available: https://hdl.handle.net/11511/56622.