642-32-0Relevant articles and documents
Novel synthetic route to octasubstituted naphthalenes from four alkynes and one olefin unit via zirconacyclopentadienes and 1,2-Diiodo-3,4,5,6- tetraalkylbenzene
Zhou, Xin,Li, Zhiping,Wang, Hui,Kitamura, Masanori,Kanno, Ken-Ichiro,Nakajima, Kiyohiko,Takahashi, Tamotsu
, p. 4559 - 4562 (2007/10/03)
1,2,3,4-Tetrasubstituted benzene derivatives were prepared by the reaction of zirconacyclopentadienes with vinyl bromide in the presence of NiCl 2(PPh3)2. 1,2-Diiodo-3,4,5,6-tetraalkylbenzenes were formed by treatment of 1,2,3,4-tetraalkylbenzenes with iodine and periodic acid in the presence of a catalytic amount of sulfuric acid. Reaction of the 1,2-diiodo-3,4,5,6-tetraalkylbenzenes with zirconacyclopentadienes in the presence of a stoichiometric amount of CuCl gave sterically crowded octasubstituted naphthalenes in moderate yields.
Preparation and conformation of octaethylbiphenylene
Taha,Marks,Gottlieb,Biali
, p. 8621 - 8628 (2007/10/03)
Dimerization of tetraethylbenzyne (generated by reaction of 1,2-dibromo-3,4,5,6-tetraethylbenzene (8) with 1 equiv of BuLi) afforded in low yield octaethylbiphenylene (3), together with a major product which was characterized as 2,3,4,5,3',4',5'-heptaethyl-2'-vinylbiphenyl (9). X-ray diffraction indicates that biphenylene 3 adopts in the crystal a conformation of approximate C(2h) symmetry with the ethyl groups within each phenylene ring arranged in an alternated up-down fashion. Notably, pairs of vicinal ethyl groups located at peri positions are oriented in a syn arrangement in the crystal. Low temperature NMR spectroscopy is consistent with the presence in solution of either the crystal conformation or a fully alternated conformation lacking any syn interaction. Molecular mechanics (MM3), semiempirical (AM1, PM3), and ab initio calculations indicate that the crystal conformation is a high energy form, and that the lowest energy conformation is the fully alternated form. The topomerization barrier of the methylene protons of the ethyl groups of 3 is 9.4 ± 0.1 kcal mol-1, which is between the rotational barriers of 8 and 1,2,3,4-tetraethylbenzene 7 (9.9 ± 0.1 and 8.2 ± 0.1 kcal mol-1, respectively). The similarity in rotational barriers suggests that a given tetraethylphenylene subunit does not markedly affect the rotational barrier of the ethyl groups of the other subunit.
