Dibenzo helicene

Jancafrk, A., RybdCek, J., Cocq, K., Vacek Chocholousovd, J., Vacek, J., PoM, R., Bed-nirova, L., Fiedler, R, Cfsrfovd, I., Stara, I. G., Stary, I. (2013). Rapid access to dibenzo-helicenes and their functionalized derivatives. Angewandte Chemie, International Edition, 52, 9970-9975. 

In general, only helicenes with six or more benzene or other rings will be treated. The lower homologs, dibenzo[c,g]phenanthrene (pentahelicene) and benzo[c]phen-anthrene will only be mentioned for comparison in some instances. 

D. Pena, A. Cobas, D. Perez, E. Guitian, L. Castedo, Dibenzo[ ,o]phenanfhro[3,4-sjpycene, a Configurationally Stable Double Helicene Synthesis and Determination of Its Conformation by NMR and GIAO Calculations, Org. Lett. 2003, 5, 1863-1866. 

Chen et al. reported novel photoswitches using C2-symmetric dibenzo-suberane-based helicenes with a tetraline-based fragment. Photoisomerization of the diastereomerically pure (P)-from (34) led to virtually exclusive formation of the (M )-form (35) at 290 nm irradiation. Upon 330 nm irradiation, (35) isomerized to (34). This photoswitch in a nematic liquid crystal was applicable to a cholesteric mesophase with modulated pitches, reversible helical senses, and a switch memory of ternary logic. Furthermore, the helicene (36)-(39) with bis-azobenzene chromophores acted as highly diastereoselective chirochromic (92 8 to 3 97) and photo-chromic (>99 <1 to 19 81) switches both in solutions and in the nematic liquid crystal. ... 

Regarding the construction of helical chirality through intramolecular cycloaddition of designed triynes, the Ni(cod)2/(7 )-Quinap catalytic system has shown nice efficiency and allows the straightforward preparation of dibenzo[6]helicenes (Scheme 7.3) [7]. 

Scheme 73 Nickel-catalyzed synthesis of dibenzo[6]helicenes.

Cataiytic transformation has also been accomplished. Kawaguchi et al. reported the palladium-catalyzed intramolecular 0-arylation of 2-[2-(pseudo)haloaryl]phenols [14]. 2-(2-Chlorophenyl)phenol (68) was converted to dibenzofuran (69) successfully in the presence of palladium(II) acetate/phosphine ligand, but the authors did not explore the scope of this reaction (Scheme 23.26). In addition, they accomplished the synthesis of fused polycyclic compounds such as dibenzo[(i,fi ]benzo[l,2-fe 4,5-fc jdifurans 70 [14] and oxa[7]helicene 71 [17] using this methodology (Scheme... 

After replacing the 3-phenanthryl group in ketone 3.590 by a 2-benzofcjphenanthryl group followed by the same synthetic procedure, dibenzo[c,g]-phenanthrene([5])helicene derivatives were produced. The phenyl substituents in highly hindered positions produced a helical bend. Such helicenes and related compounds attract attention due to their unusual structure and important optical and electronic properties [91, 297-299]. 

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