Transition structures, energetics, and nucleus-independent chemical shifts for 6 pi electrocyclizations of dienylketenes to cyclohexadienones: A DFT study

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 less exothermic or even endothermic. The effect of aromaticity is slightly less pronounced for dienylketenes carrying five-membered heterocyclic aromatic substituents. Slightly distorted planar transition structures have been located for these types of cyclizations. Forming bond lengths in transition structures range from 1.950 to 2.339 Angstrom.


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...
Reactions of 2-substituted epichlorohydrins
Tanyeli, Cihangir; Akhmedov, IM; Ozgul, E; Kandemir, CG (Informa UK Limited, 1996-01-01)
2-Substituted epichlorohydrins have been synthesized by starting with 1,2-dichloro acetone and various alkyl and aryl halides via dichlorohydrins followed by cyclization. The reactive 2-substituted epichlorohydrins were subjected to nucleophilic attacking of azide and cyanide ions to afford corresponding beta-azido alcohols and alpha,beta-unsaturated nitriles.
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...
Generation of acyl anion equivalents from acylphosphonates via phosphonate-phosphate rearrangement: A highly practical method for cross-benzoin reaction
Demir, Ayhan Sıtkı; Reis, O; Igdir, AC; Esiringu, I; Eymur, S (American Chemical Society (ACS), 2005-12-09)
Acylphosphonates are potent acyl anion precursors that generate acyl anion equivalents under the promotion of cyanide anion via phosphonate-phosphate rearrangement. These anions readily react with aldehydes to provide cross-benzoin products. In this way it is possible to synthesize a variety of aromatic-aromatic, aromatic-aliphatic, and aliphatic-aromatic benzoins. Moreover the reaction of benzoylphosphonate with potent electrophile 2,2,2-trifluoroacetophenone provided the corresponding aldehyde-ketone coup...
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...
Citation Formats
M. Zora, “Transition structures, energetics, and nucleus-independent chemical shifts for 6 pi electrocyclizations of dienylketenes to cyclohexadienones: A DFT study,” JOURNAL OF ORGANIC CHEMISTRY, pp. 1940–1947, 2004, Accessed: 00, 2020. [Online]. Available: