Cyclic aromatization

Polycyclic aromatic hydrocarbons undergo electrophilic aromatic substitution when treated with the same reagents that react with benzene In general polycyclic aromatic hydrocarbons are more reactive than benzene Most lack the symmetry of benzene how ever and mixtures of products may be formed even on monosubstitution Among poly cyclic aromatic hydrocarbons we will discuss only naphthalene and that only briefly Two sites are available for substitution m naphthalene C 1 and C 2 C 1 being normally the preferred site of electrophilic attack... 

Imidazole and its derivatives form an interesting and important class of hetero cyclic aromatic amines Imidazole is approximately 100 times more basic than pyndme... 

Dihydronaphthalene is often used as a model olefin in the study of epoxidation catalysts, and very often gives product epoxides in unusually high ee s. In 1994, Jacobsen discovered in his study on the epoxidation of 1,2-dihydronaphthalene that the ee of the epoxide increases at the expense of the minor enantiomeric epoxide.Further investigation led to the finding that certain epoxides, especially cyclic aromatically conjugated epoxides, undergo kinetic resolution via benzylic hydroxylation up to a krei of 28 (Scheme 1.4.9). 

Mechanistically the observed stereospecificity can be rationalized by a concerted, pericyclic reaction. In a one-step cycloaddition reaction the dienophile 8 adds 1,4 to the diene 7 via a six-membered cyclic, aromatic transition state 9, where three r-bonds are broken and one jr- and two cr-bonds are formed. The arrangement of the substituents relative to each other at the stereogenic centers of the reactants is retained in the product 10, as a result of the stereospecific y -addition. 

Heterocyclic aromatic nitro compounds are more reactive toward nucleophiles than carbo-cyclic aromatic nitro compounds Various heterocyclic aromatic nitro compounds are thus converted into the corresponding pyrroles by the Barton-Zard reaction fEq 10 37 ... 

Exceptions to this statement have been noted in the case of cyclic aromatic ketones bearing electron-donating groups in ortho and para positions Bhalerao, U.T. Thyagarajan, G. Can. J. Chem., 1968, 46, 3367 Tomita, M. Minami, S. Uyeo, S. J. Chem. Soc. C, 1969, 183. 

Another example is benzene, a cyclical aromatic compound. 

Behan, J. M. Dean, F. M. Johnstone, R. A. W. Photoelectron spectra of cyclic aromatic ethers the question of the Mills-Nixon effect. Tetrahedron 1976, 32, 167-171. 

The oxidation of poly(N-phenyl-3,4-dimethylenepyrroline) with DDQ or Pd/C in nitrobenzene gave in a cyclic aromatic amine polymer with repeating pyrrole rings in the polymer backbone. Using Pd/C in... 

The question of multiple bonding between boron and carbon when there is no cyclic aromatic character to be gained, as for example in vinylboranes (structures 5a and 5b), is more difficult to decide. 

Intramolecular arylation of G-H bonds gives cyclic aromatic compounds. In this intramolecular arylation, the carbon-palladium cr-bond is first formed by the oxidative addition of Pd(0) species and then the resulting electrophilic Pd(n) species undergoes the intramolecular G-H bond activation leading to the formation of the palladacycle, which finally affords the cyclic aromatic compounds via reductive elimination.87 For example, the fluoroanthene derivative is formed by the palladium-catalyzed reaction of the binaphthyl triflate, as shown in Scheme 8.88 This type of intramolecular arylation is applied to the construction of five- and six-membered carbocyclic and heterocyclic systems.89 89 89 ... 

Cyclic 1,2-diketones, 24 594 Cyclic acrolein acetals, 2 271 Cyclic amidine curing agents, 10 410 Cyclic amidines, 10 412 Cyclic (aromatic disulfide) oligomers, 23 712... 

Cyclic aromatic disulfides, polymerization reactions of, 23 706 Cyclic (arylene) disulfides, 23 712 Cyclic batch adsorption processes, 1-613 Cyclic bis(arylene tetrasulfide)s, 23 712 Cyclic carbon, polymer materials with, 15 177... 

The propargylic alcohol 102, prepared by condensation between 100 and the lithium acetylide 101, was efficiently reduced to the hydrocarbon 103, which on treatment with potassium tert-butoxide was isomerized to the benzannulated enyne-allene 104 (Scheme 20.22) [62], At room temperature, the formation of 104 was detected. In refluxing toluene, the Schmittel cyclization occurs readily to generate the biradical 105, which then undergoes intramolecular radical-radical coupling to give 106 and, after a prototropic rearrangement, the llJ-f-benzo[fo]fluorene 107. Several other HJ-f-benzo[fo]fluorenes were likewise synthesized from cyclic aromatic ketones. 

Von Oettingen WF. 1955. The halogenated aliphatic, olefinic, cyclic, aromatic, and aliphatic-aromatic hydrocarbons including the halogenated insecticides, their toxicity and potential dangers. Washington, DC U.S. Public Health Service. PHS Publication No. 414, 15-28. 

Cooks, R.G. Howe, I. Tam, S.W. Williams, D.H. Studies in Mass Spectrometry. XXIX. Hydrogen Scrambling in Some Bi-cyclic Aromatic Systems. Randomization Over Two Rings. J. Am. Chem. Soc. 1968, 90,4064-4069. 

When the suffixes a7nea.nd -eneshow up in a compound name like decane or decene they are usually consistent with the alkane and alkene definitions, but not always. Benzene is a cyclic aromatic hydrocarbon, not a straight chain molecule naphthenes are cyclic compounds. 

GUNDERSON AND THRANE Poly cyclic Aromatic Hydrocarbons... 

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