109376-33-2Relevant academic research and scientific papers
Formation of 5,6- and 7,8-Dihydrohexahelicene: Mechanistic Details of the Rearrangement of the Primary Photocyclization Product of 2-Styrylbenzophenanthrene in the Presence of a Base
Prinsen, Wim J. C.,Laarhoven, Wim H.
, p. 3689 - 3694 (1989)
Irradiation of 2-styrylbenzophenanthrene (1) in alkylamines or basic alcoholic solution results in the formation of a mixture of two dihydrohexahelicenes (5,6- and 7,8-dihydrohexahelicene, 5 and 6).The ratio of 5 and 6 depends on the kind of solvent.In alkylamine 6 is the favored dihydrohexahelicene.In basic alcoholic solution 5 is the preferred product.Deuteration of the solvent causes a change in the ratio of 5 and 6 in favor of 5.The reaction starts with the deprotonation of the primary formed, unstable 16d,16e-dihydrohexahelicene (2), followed by a protonation step.The site of this protonation determines the ratio of 5 and 6 and depends upon the acidity of the protonating agent, an alkylammonium cation or solvent molecule, and the electron densities at the various possible sites for protonation in the intermediate.Irradiation of 1 in several chiral alkylamines yielded optically enriched 6.
Syntheses, conformational analyses, X-ray analyses and force-field-calculations of 7,8-dihydrohexahelicene and 5,6-dihydrohexahelicene
Prinsen, W. J. C.,Laarhoven, W. H.,Bosman, W. P.,Behm, H.,Beurskens, P. T.
, p. 575 - 582 (2007/10/02)
The photocyclization of 2-styrylbenzophenanthrene (1) in n-butylamine yields a mixture of hexahelicene (3) and two dihydrohexahelicenes (5 and 6).Both dihydrohexahelicenes could be isolated from the irradiation mixture as pure compounds by chromatography on a silica gel coated with R(-)-TAPA, a chiral stationary phase develeoped for the resolution of the enantiomers of hexahelicene (3).The NMR spectra of 5,6-dihydrohexahelicene (5) and (7,8-dihydrohexahelicene (6) exhibit remarkable differences in the aromatic region.These differences are attributed to the location of the alicyclic ring in the hexahelicene skeleton.The X-ray structure analyses of the dihydrohexahelicenes 5 and 6 demonstrate that, in the crystalline state, both isomers occur in only one of two possible conformations.The NMR spectra of the two compounds lead to the conclusion that, in solution, the same conformation as in the solid state is highly preferred, although the existence of the second conformation cannot be completely excluded.Structural analyses by force-field calculations corroborate this conclusion.
