69103-81-7

Upstream product

• 20508-11-6 (Z)-1-Phenyl-2-(2-benzophenanthrenyl)ethylene 
• 81701-08-8 2,7-distyrylnaphthalene 

Relevant academic research and scientific papers

The influence of the chiral environment in the photosynthesis of enantiomerically enriched hexahelicene

The enrichment of one of the enantiomers (P or M) of hexahelicene (3) synthesized by the photochemical cyclodehydrogenation of 2-styryl-benzophenanthrene (1) in chiral media has been (re)investigated.Four different chiral solvents, two cholesteric liquid crystals, two chiral crystals, all at several temperatures, and two chiral polymers were used as media.To avoid erroneous values from circular-dichroism (CD) measurements due to contributions of chiral side-products, the enantiomeric excess (ee) was determined by HPLC analysis.In general the observed ee is small ( 7percent).In chiral solvents the ee increases with decreasing temperatures.In the liquid crystals the macroscopic helix of the cholesteric phase has a small but distinct effect on the ee, probably due to the preferred fitting of one enantiomer of Z-1 to the helix of the 'solvent'.In chiral crystals the ee is relatively larger.A peculiar effect is observed when 1 is irradiated in ethyl (S)-(+)-O-(4-phenylbenzoyl)lactate.Below -19 deg C the M enantiomer and above -14 deg C the P enantiomer of 3 is the preferred photoproduct.In the polymer triacetylcellulose, M-hexahelicene is formed in 4.5percent excess; in β-cyclodextrine only a very small amount of 3 is formed, due to the preferred photo-isomerization into E-1.

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

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

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.

Conformational studies on helicenes VII. Synthesis and conformation of 5,6-dihydrohexahelicene

Irradiation of 2,7-distyrylnaphthalene or 2-styrylbenzophenanthrene under completely oxygen-free conditions gives rise to the formation of 5,6-dihydrohexahelicene (2) as a consequence of H-shifts in the primary formed cyclization product.The conformation of 2 was analyzed by NMR spectroscopy.From the chemical shifts of the aromatic protons, the coupling constants of the saturated moiety and the temperature independence of the spectrum it could be concluded that 2 occurs in one conformation, in which the axial proton at C(5) is directed towards the opposite ring.The resemblance of the spectra of 2 and 1-phenylbenzophenanthrene affirms that this conformation is the less hindered one.