Free-radical cyclization approach to polyheterocycles containing pyrrole and pyridine rings

A wide range of derivatives with new pyrido[2,1-a]pyrrolo[3,4-c]isoquinoline skeleton was synthesized by free-radical intramolecular cyclization of o-bromophenyl-substituted pyrrolylpyridinium salts using the (TMS)3SiH/AIBN system. The cyclization provides generally good yields of pyrido[2,1-a]pyrrolo[3,4-c]isoquinoline hydrobromides having no additional radical-sensitive substituents. The free bases can be obtained from the synthesized hydrobromides in quantitative yield by basification at room temperature. The selectivity control of intramolecular arylation was achieved by replacing the halogen: the use of 1-(2-(ortho-bromophenyl)-4-(ortho-iodophenyl)pyrrol-3-yl)pyridinium bromide makes it possible to obtain a monocyclization product, and the bicyclization product from the dibromo derivative. The procedure is also applicable to obtain 3-arylpyrido[2,1-a]pyrrolo[3,2-c]isoquinoline derivatives including 2-unsubstituted skeletons that are inaccessible via Pd-catalyzed cyclization.

A new approach towards synthesis of benzo[b]fluorene core

New approach towards synthesis of benzo[<em>b</em>]fluorene core is described. The model compound, 10-methoxy-11<em>H</em>-benzo[<em>b</em>]fluoren-11-one was prepared in five steps starting from dibenzylmalonic acid. The key step was the metal catalyzed rearrangement of 3,3’-dihalo-2,2’-spirobiindan-1,1’-dione. The choice and proper activation of the metal was critical for the assembly of the benzo[<em>b</em>]fluorenone system. The zinc mediated rearrangement of the corresponding dibromo derivative led to the 10-hydroxy-11<em>H</em>-benzo[<em>b</em>]fluoren-11-one derivative in 52% yield. The structure of the product was established by spectroscopic methods and was additionally confirmed by standard methylation reaction to the 10-methoxy derivative, which is known in the literature.

Conformational analysis of the bicyclo - [4.4.1]undecan-11-one ring system

The first conformational analysis of a bicyclo[4.4.1]undecan-11-one system (1) is presented. Based on low-temperature 13C NMR line-broadening measurements and an X-ray structure of the 1,6-dibromo derivative (2), this ketone adopts a chiral conformation with approximate C2 symmetry about an axis containing the >C=0 bond. The observed NMR line-broadening results are consistent with a dynamic interchange of M and P enantiomeric C2 conformations, or expressed another way, the "effective" development of an additional Cs symmetry plane bisecting the molecule at right angles to the plane containing the one carbon bridge (overall average C2v symmetry). This process has a ΔH‡ barrier of 42 kJ mol–1 for ketone 1 (43 kJ mol–1 for 2).Key words: bicyclo[4.4.1]undecan-11-one, conformational analysis, NMR line broadening, X-ray structure, enantiomers.

Photoleitende Flüssigkristalle aus der Reihe der 2,3,6,7-Tetrakis(alkoxy)triphenylene / Liquid Crystals in the Series of 2,3,6,7-Tetraalkoxytriphenylenes

Stepwise bromination of the triphenylene 1 leads regioselectively to the monobromo and the dibromo compound 2 and 3, respectively (Scheme 1). In contrast to 1 and 2, the dibromo derivative 3 as well as the nitrile 4. obtained from 3 and CuCN, form thermotropic mesophases Dh. On irradiation of 3 and 4 a photocurrent can be measured in the crystalline state and an enhanced photocurrent in the LC phase.