Search results for "Cyclobutene"
showing 9 items of 9 documents
Force Distribution Analysis of Mechanochemically Reactive Dimethylcyclobutene
2013
Internal molecular forces can guide chemical reactions, yet are not straightforwardly accessible within a quantum mechanical description of the reacting molecules. Here, we present a force-matching force distribution analysis (FM-FDA) to analyze internal forces in molecules. We simulated the ring opening of trans-3,4-dimethylcyclobutene (tDCB) with on-the-fly semiempirical molecular dynamics. The self-consistent density functional tight binding (SCC-DFTB) method accurately described the force-dependent ring-opening kinetics of tDCB, showing quantitative agreement with both experimental and computational data at higher levels. Mechanical force was applied in two different ways, namely, exter…
Regioselective Annulation of Alicyclic−Aromatic Dienes with 3-Halo-3-cyclobutene-1,2-diones. Synthesis of Annulated α-Halobenzocyclobutenones1
1998
4-(1-Cycloalken-1-yl)-1,2-dialkoxybenzenes 8, 10, and 11 and 5-(1-cycloalken-1-yl)-1,3-benzodioxoles 12−15 react with the semisquaric halides 5a and 5b in a dehydrative annulation process to give the annulated α-halobenzocyclobutenones 9a,b and 16a,b−21a,b in poor to good yields (20−76%). The reaction failed with alicyclic−aromatic dienes having no or only one alkoxy group in the benzene ring. The dehydrative annulation process could be extended to 4-(3,4-dimethoxyphenyl)-1,2-dihydronaphthalene (24), affording the highly annulated α-chlorobenzocyclobutenone 25 in 50% yield. In the case of 5-(1-cyclobuten-1-yl)-1,3-benzodioxole (22), reaction with the semisquaric halides 5a,b yielded the dic…
The electronic substituent influence on the thermally allowed electrocyclic interconversion cyclobutene/butadiene. A MNDO study
1984
The effects of donor/acceptor substitution on the conrotatory cyclobutene/butadiene interconversion have not yet been experimentally studied. MNDO Synchronous Transit/MINIMAX calculations for all possible combinations of NH2/NH3 + 3 groups at the fissile single bond reveal very large substituent effects on the opening reactions and reverse cyclisations. Diamino(1b/2b), diammonio-(1c/2c) and amino-ammonio-substitutions (1d/2d) change the activation energy of the reference ring opening reaction (1a →2a) from 49.9 kcal/mol to 34.7, 29.8 and 26.0 kcal/mol, respectively. This rate enhancement parallels the monotone shift of the transition state pathcoordinate towards the cyclobutenes. Relative t…
Benzoxetes and Benzothietes ¾ Heterocyclic Analogues of Benzocyclobutene
2012
Benzo-condensed four-ring heterocycles, such as benzoxetes 1 and benzothietes 3 represent multi-purpose starting compounds for the preparation of various higher heterocyclic ring systems. The thermal or photochemical valence isomerizations between the benzenoid forms 1,3 and the higher reactive o-quinoid structures 2,4 provide the basis for the synthetic applications. On the other hand, this valence isomerization impedes in particular the generation and storage of 1 because the thermal equilibrium 1 ⇆ 2 is completely on the side of 2. Thus, the number of erroneous or questionable benzoxete structures published to date is surprisingly high. On the contrary, the thermal equilibrium 3 ⇆ 4 is o…
ChemInform Abstract: Benzoxetes and Benzothietes - Heterocyclic Analogues of Benzocyclobutene
2012
Benzo-condensed four-ring heterocycles, such as benzoxetes 1 and benzothietes 3 represent multi-purpose starting compounds for the preparation of various higher heterocyclic ring systems. The thermal or photochemical valence isomerizations between the benzenoid forms 1,3 and the higher reactive o-quinoid structures 2,4 provide the basis for the synthetic applications. On the other hand, this valence isomerization impedes in particular the generation and storage of 1 because the thermal equilibrium 1 2 is completely on the side of 2. Thus, the number of erroneous or questionable benzoxete structures published to date is surprisingly high. On the contrary, the thermal equilibrium 3 4 is on th…
The rel-R,R-enantiomer of 7-[7-hydroxybicyclo[4.2.0]octa-1(6),2,4-trien-7-yl]bicyclo[4.2.0]octa-1(6),2,4-trien-7-ol
2018
A single crystal of the rel-R,R-enantiomer of the title compound, C16H14O2, was analyzed. The molecular structure is characterized by nearly planar cyclobutene rings and a torsion angle of the diol unit of 68.3 (2)°. Strands parallel to the b axis are built from diols connected via hydrogen bonds.
CCDC 197178: Experimental Crystal Structure Determination
2004
Related Article: M.L.Calatayud, J.Sletten, I.Castro, M.Julve, G.Seitz, K.Mann|2003|Inorg.Chim.Acta|353|159|doi:10.1016/S0020-1693(03)00221-4
CCDC 197176: Experimental Crystal Structure Determination
2004
Related Article: M.L.Calatayud, J.Sletten, I.Castro, M.Julve, G.Seitz, K.Mann|2003|Inorg.Chim.Acta|353|159|doi:10.1016/S0020-1693(03)00221-4
CCDC 197177: Experimental Crystal Structure Determination
2004
Related Article: M.L.Calatayud, J.Sletten, I.Castro, M.Julve, G.Seitz, K.Mann|2003|Inorg.Chim.Acta|353|159|doi:10.1016/S0020-1693(03)00221-4