Photobromination of indane: preparation of bromoindenones and ready access to benzo[c]fluorenone skeleton

Highly brominated biphenylenes as precursors for the convenient synthesis of 5,6,8,10-tetrabromobenzocyclooctene

An efficient synthesis is described of hexabromides 5 and 6 by photobromination of biphenylene (1). Double dehydrobromination of hexabromides 5 and 6 with t-BuOK affords 5,6,8,10-tetrabromobenzocyclooctene (7) in nearly quantitative yield. The tetrabromide 7 is a valuable precursor for the preparation of functionalised substituted benzocyclooctenes (benzo[8]annulenes).

Unusual traits of cis and trans-2,3-dibromo-1,1-dimethylindane on the way from 1,1-dimethylindene to 2-bromo-, 3-bromo-, and 2,3-dibromo-1,1-dimethylindene

Do not rely on the widely accepted rule that vicinal, sp³-positioned protons in cyclopentene moieties should always have more positive ³J NMR coupling constants for the cis than for the trans arrangement: Unrecognized exceptions might misguide one to wrong stereochemical assignments and thence to erroneous mechanistic conclusions. We show here that two structurally innocent-looking 2,3-dibromo-1,1-dimethylindanes violate the rule by means of their values of ³J(cis) = 6.1 Hz and ³J(trans) = 8.4 Hz. The stereoselective formation of the trans diastereomer from 1,1-dimethylindene was improved with the tribromide anion (Br₃⁻) as the brominating agent in place of elemental bromine; the ensuing, regiospecific HBr elimination afforded 3-bromo-1,1-dimethylindene. The addition of elemental bromine to the latter compound, followed by thermal HBr elimination, furnished 2,3-dibromo-1,1-dimethylindene, whose Br/Li interchange reaction, precipitation, and subsequent protolysis yielded only 2-bromo-1,1-dimethylindene.

Synthesis of 1,3-dibromo-2-aryl-1H-indenes via NBS mediated unusual bromination of 2-alkynylbenzaldoximes

An interesting side-pathway leading to 1,3-dibromo-2-aryl-1H-indenes as opposed to isoquinoline N-oxides via NBS mediated bromination of 2-alkynylbenzaldoximes.

Synthesis of Bromoaminoindane and Bromoaminoindanone Derivatives

The bromination reactions of 5-aminoindane, 5-acetamidoindane, and 5-acetamidoindan-1-one were investigated using NBS, molecular bromine and photobromination, and the optimum reaction conditions were presented. The reaction of 5-aminoindane with glacial acetic acid at reflux temperature resulted in the formation of 5-acetamidoindane in high yield. 5-Acetamidoindan-1-one was generated by the reaction of 5-acetamidoindane with CrO3 in acetic acid. Selective bromination at C-6 position of 5-acetamidoindane was achieved by treatment of title compound with bromine in acetic acid and thus afforded 5-acetamido-6-bromoindane. Further bromination reactions of bromoindanones were achieved in various reaction conditions.

Synthesis of New Anthracene Derivatives

An efficient synthesis is described for hexabromoanthracenes 3 and 4 by direct bromination of 9,10-dibromoanthrecene 2. Whereas base-induced elimination of hexabromide 3 with t-BuOK gave 2,3,9,10-tetrabromoanthracene 5, the reaction of hexabromide 4 with DBU afforded 1,3,9,10-tetrabromoanthracene 6 as the sole product. Tetrabromide 5 was also obtained by aromatization of 1,4-dinitroxy-2,3,9,10-tetrabromo-1,2,3,4-tetrahydroanthracene 17. Efficient and convenient synthetic routes are described for the preparation of dinotroxy 17, dimethoxy 23, and dihydroxides 18 and 19 with silver-induced substitution of hexabromides 3 and 4. The hydroxy compounds 19 and 18 were converted to diepoxide 20 and monoepoxide 21, respectively, with sodium methoxide. Base-promoted aromatization of dimethoxide 23 afforded dibromomonomethoxides 26 and 27. Bromoanthracenes and isomeric arene oxides constitute valuable precursors for the preparation of functionalized substituted anthracene derivatives that are difficult to prepare by other routes.

Indene and Pseudoazulene Discotic Liquid Crystals: A Synthetic and Structural Study

Several new liquid-crystalline indene and pseudoazulene systems are reported. These molecules give rise to either columnar hexagonal mesophases and/or columnar plastic phases. The unique nature of these compounds stems from their non-classical discotic structure. Although the molecules have rigid aromatic cores, they lack terminal tails and instead the polarizable atoms (S, halogens) or polar groups (CN, CO) act as unusual soft parts. On the basis of many structurally related materials, we conclude that for this type of compound molecular stacking in the solid state is a prerequisite for the appearance of a columnar mesophase, although other intermolecular interactions within the layers are also important in establishing liquid-crystalline order. The behavior reported for these mesomorphic molecules opens up new possibilities in the search for related molecular interactions that might be useful for the construction of supramolecular architectures with particular properties.