10060-20-5Relevant articles and documents
Synthetic Applications in Radical/Radical Cationic Cascade Reactions
Rinderhagen, Heiko,Mattay, Jochen
, p. 851 - 874 (2007/10/03)
Oxidative photoinduced electron transfer (PET) reactions have been performed with various cyclic cyclopropyl(vinyl) silyl ethers bearing an olefinic or acetylenic side chain. The reactions result in bi- to tetracyclic ring systems via a fragmentation-radical/radical cationic addition reaction pathway with well defined ring juncture. The mode of cyclisation (endo/exo) can be partially controlled by addition of nucleophiles due to the suppression of radical cationic reaction pathways. Quantum chemical calculation of the cyclisation transition states underline the experimentally found selectivities. Additional mechanistic studies concerning the saturation step reveal that the final radical is saturated mostly by the solvent and traces of water in the solvent.
The syntheses and conformational studies of [n](2,4)heterophanes and [7](3,5)pyrazolophane
Hirano,Hiyama,Fujita,Kawaguti,Hayashi,Nozaki
, p. 2633 - 2640 (2007/10/09)
Synthetic sequences from (n + 3)-membered 2-cycloalkenones provide furan, thiophene and pyrrole derivatives bridged at the 2,4-positions by n-methylene chains (n = 6, 7, and 9) as well as a pyrazole derivative bridged at the 3,5-positions (n = 7). The molecular geometry as a function of the chain length has been investigated spectrometrically. The aliphatic chain of [7](2,4)pyrrolophane and [7](3,5)pyrazolophane is found to reside in the one side of the respective heteroaromatic rings even at 205°, whereas that of [7](2,4)thiophenophane flips up and down the thiophene ring upon heating, the energy barrier ΔGc≠ being 18·2 kcal/mol (Tc 111°C at 60 MHz). The conformational behaviour of the heptamethylene chain is thus dependent on the angle between the bonds connecting each heteroaromatic carbon with the benzylic one. Though the hexamethylene chain of the [6](2,4)heterophanes is fixed to the one side of the aromatic ring, the nonamethylene chain of the [9]-homologues is rapidly moving between the both sides even at room temperature. The red-shifts of the B-bands are attributed to the distorted, nonplanar heteroaromatic rings. The mass spectra of these heterophanes indicate the initial C(1)-C(2) fission of the polymethylene chain probably due to the steric strain of the systems.