Cyclodehydrogenation compounds

These methods utilize molecules of type B (p. 362) (=104) a. Synthesis of Benzofurans by Thermal Ring Closure and Cyclodehydrogenation (Thermal, Catalytic or Photochemical) of o-Substituted Phenols. The Hansch Reaction. o-Alkylhydroxy-compounds on heating with a suitable catalyst give either a benzofuran or a 2,3-dihydrobenzo-furan with the same number of carbon atoms.285-292 Side products are formed by decomposition of the starting material. The initial phenol can be o-alkylated and ring-closed in one stage. 

Catalytic cyclodehydrogenation of 5-amino-2-ethylthiophenol affords 6-aminobenzo[6]thiophene.239,241 6-Acetamido-2,3-di-bromo-,77 6-acetamido-2-bromo-3-methyl-,102 6-acetamido-3-bromo-2-methyl-,102 and 6-acetamido-3-bromobenzo[f>]thiophene107 may be obtained from the corresponding 6-acetyl compound by means of the Schmidt reaction. In some cases the 6-acetamido compound is accompanied by a smaller amount of the amine sulfate.102,107 6-Aminobenzo[6]thiophene may be converted into 6-chloro- or 6-cyanobenzo[6]thiophene by means of the Sandmeyer reaction.241... 

Howsam and Jones, 1998). For example, the pyrolysis of naphthalene can yield a range of HMW species such as perylene and benzofluoranthenes, possibly as a result of cyclodehydrogenation of the binaphthyls (Howsam and Jones, 1998). This may be particularly important for compounds that are deposited on the walls of open fireplaces along with soot particulates close to the hot zone of the flame. 

Benzoannelated triquinacenes [154],fenestranes [155], and centrohexaquinace-nes [156] are nonplanar aromatic hydrocarbons with an interesting molecular architecture. Extensive preparative work has been accomplished especially by Kuck and his coworkers [154-156] to explore different routes towards these compounds. Although the syntheses usually do not involve formation of aryl-aryl bonds or even condensed aromatic systems, we have chosen to depict three successful routes that all result in the centrohexaindane 116 in Scheme 54, whereas the probably most convenient route A is illustrated in more detail [156]. The final reaction steps along routes A and B are typical aromatic electrophilic alkylation reactions, and along route C a threefold cyclodehydrogenation cata-... 

Phenolic Cyclization and Coupling Reactions. The oxidation of phenolic compounds which either do not possess benzylic hydrogen atoms, or which have an alternative reaction pathway, can result in a variety of interesting products. Cyclodehydrogenation reactions leading to oxygen heterocycles represent... 

The oxidative dimerization of phenol 22.1 was simulated in vitro. Exposure of this compound to the complex Cu(NO 3) 2-pyridine gave rise to dimers 23.10 and 23.11 by a C-C coupling reaction. Compound 23.11 could be cyclodehydrogenated to 23.10 by reaction with DDQ. On the other hand, exposure of phenol 22.1 to K3Fe(CN)6 gave the product (22.3) of a C-0 coupling, which was then transformed into 23.12 by DDQ cyclodehydrogenation 140) (Scheme 9). 

Kuwanon M (160) 136), mp 252-254 °C, [a]o -2.0°, C50H48O12, was found to have a hypotensive action in hypertensive rats (2 mg/Kg, i.v.). Its structure was derived on the basis of spectral evidence. Kuwanon M (160) is optically active and is presumably formed by an enzymatically-controlled Diels-Alder type reaction between kuwanon C (33) and a coexisting dehydro derivative and subsequent cyclodehydrogenation. Takasugi et al. have isolated a similar compound, dimora-cin (101) 84), mp 238-240 °C, [a]o — 5°, as a phytoalexin from diseased... 

The addition of organometallic compounds to benzoquinone derivatives was an early approach for the synthesis of PAHs. The diol obtained was subsequently aromatized and cyclodehydrogenated to give the PAH [19-22]. An example of such an approach is depicted in Scheme 3. Clar et al. synthesized a cata-hexabenzocoronene 9 by this method. 

With this method, a methoxy substituted polyphenylene precursor was synthesized. The molecule was adsorbed on a copper surface and the cyclodehydrogenation was thermally induced directly on the surface [46]. The synthesis of substituted HBCs permits tuning of the properties in this class of compounds, for example in a columnar supramolecular assembly [47]. The influence of substitution at the periphery with either oligoether (water soluble) or alkyl chains with different degrees of branching and different lengths has been studied [48]. 

Smith JG, Levi EM (1972) The interaction of alkali metals with unsaturated heterocyclic compounds 1. 2,3-Diphenylquinoxaline and its cyclodehydrogenation to dibenzo[a,c] phenazine. J Organomet Chem 36(2) 215-226. doi 10.1016/S0022-328X(00)80668-3... 

Halleux and coworkers later reported the synthesis of parent HBC using two different methods (Scheme 3.7) [32]. The cyclodehydrogenation of hexaphenyl-benzene 11 by molten AlCh/NaCl and the reaction of dibenz-l,9 2,3-anthrone 12 with Zn/ZnCl2 both produced HBC. Two other hydrocarbons, tetrabenz-4,5 6,7 ll,12 13,14-peropyrene and tetrabenz-l,2 3,4 8,9 10,ll-bisanthene, have been isolated from the reaction of compound 12 with Zn/ZnCl2. 

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