Polycyclic heteroaromatics

In order to differentiate between radical and cationic pathways of nonconcerted epoxidation, tests using radical and electrophilic PPP superdelocalisabilities have been carried out for the metabolic factor of methylated and N-heteroaromatic polycycles [19],... 

Rational substrate design, with appropriately functionalized aryl azides, has been shown to afford a variety of fused heteroaromatic polycycles. One report by Smalley et al. from the University of Salford describes exploitation of the Dimroth process to afford l,2,3-triazolo[l,5-a]quinazolines from o-azidobenz-aldehyde (42), o-azidoacetophenone, and benzonitrile with various active methylene substrates. It is interesting that the authors found an organic base, piperidine, was optimal for some substrates, while either sodium ethoxide or Amberlite resin worked better for others. 

Gross, M. Bilrli, R. Jones, P. Garcia, M. Batiste, B. Kaizerman, J. Moser, H. Jising, V. Hoch, U. Duan, J.-X. Tanaka, R. Johnson, K.W. Pharmacology of novel heteroaromatic polycycle antibacterials. Antimicroh.Agents Chernother., 2003, 47, 3448-3457. [LG-MS linezolid vancomycin]... 

A new thermal preparation ot fluorinated species is copyrolysis Copyrolysis of fluorinated compounds like perfluorobenzene, fluorinated aromatic anhydndes, and fluorinated heteroaromatics with tetrafluoroethylene or other fluonnated olefins is a useful method of preparing fluorinated olefins [88 89], functionalized fluoroaromatics [90 91 92, 93, 94, 95], fluonnated benzocycloalkanes [80, 96, 97, 98, 99, 700], fluorinated heterocycles [80, 93, 101, 102, 103], and fluonnated polycyclic compounds [104] (equations 19 and 20)... 

Alkyl radicals generated efficiently from allylsulfones in 80% aqueous formic acid induced a cyclization reaction on aromatic and heteroaromatic compounds to provide polycyclic aromatic and heteroaromatic derivatives (Eq. 7.17).37... 

The flash evaporation pyrolysis gas chromatography method [16] as described in section 11.1.4 for the determination of polycyclic aromatic hydrocarbons, haloorganics, aliphatic hydrocarbons, heteroaromatics, elemental sulphur and pyrolysis products of synthetic polymers in soils has also been applied to non-saline sediments. 

All polycyclic pigments, with the exception of triphenylmethyl derivatives, comprise anellated aromatic and/or heteroaromatic moieties. In commercial pigments, these may range from systems such as diketopyrrolo-pyrrol derivatives, which feature two five-membered heteroaromatic fused rings (DPP pigments) to such eight-membered ring systems as flavanthrone or pyranthrone. The phthalo-cyanine skeleton with its polycylic metal complex is somewhat unique in this respect. 

Fluoropyridines form valuable starting materials for a range of disubstituted pyridines because, after lithiation, nucleophilic substitution of fluoride (sometimes via the N-oxide) can be used to introduce, say, N or O substituents as in 191 and 192 (Scheme 96). Subsequent annelations can allow complex polycyclic heteroaromatics to be constructed. ... 

Dewar MJS, Rogers H (1962) Pi-complexes. 2. Charge transfer spectra of pi-complexes formed by tetracyanoethylene with polycyclic aromatic hydrocarbons and with heteroaromatic boron compounds. J Am Chem Soc 84 395... 

Flash-vacuum pyrolysis has been utilized to synthesize complex thiophene-containing polycyclic hydrocarbons from alkynyl-substituted thiophenes and chlorovinyl-substituted thiophenes <99TL2789>. For example, the bowl-shaped heteroaromatic thiophene 92 was prepared by flash-vacuum pyrolysis of benzotrithiophene 91 <99CC1859>. 

Aromatic and heteroaromatic rings are the heart of pharmaceutical design. Several useful methods for monocyclic and polycyclic aromatic ring construction have recently been reported. 

Fortunately, there is now a comprehensive body of knowledge on the metabolic reactions that produce reactive (toxic) intermediates, so the drug designer can be aware of what might occur, and take steps to circumvent the possibility. Nelson (1982) has reviewed the classes and structures of drugs whose toxicities have been linked to metabolic activation. Problem classes include aromatic and some heteroaromatic nitro compounds (which may be reduced to a reactive toxin), and aromatic amines and their N-acylated derivatives (which may be oxidized, before or after hydrolysis, to a toxic hydroxylamine or iminoquinone). These are the most common classes, but others are hydrazines and acyl-hydrazines, haloalkanes, thiols and thioureas, quinones, many alkenes and alkynes, benzenoid aromatics, fused polycyclic aromatic compounds, and electron-rich heteroaromatics such as furans, thiophenes and pyrroles. 

The trend observed with the polycyclic hydrocarbons (see preceding section), namely that the product radical anions (ArNu ) are more stable than those derived from the simple benzene analogs, is even more evident with the heteroaromatic substrates and, as a consequence, fragmentation processes are minimized.41 For example, 2-chloroquinoline is the only substrate of many studied to undergo a substitution reaction with PhCH2S- ion without fragmentation of the benzyl-S bond,103 and to react with diphenyl-arsenide ion without scrambling of the aryl moieties.25... 

The procedure is of value for the formylation of polycyclic aromatic and heteroaromatic systems, phenols and phenolic ethers. 

Superacid-promoted dicationic species containing heteroaromatic rings, where positive charge centres migrate through consecutive deprotonation-reprotonation steps, undergo cyclization reactions followed by aromatization and superacid-promoted elimination of benzene (Scheme 10).31 The process leads to the synthesis of aza-polycyclic aromatic compounds in moderate to good yields. Seven examples include pirazole, oxazole, and thiazole heterocycles. 

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