Ortho-fused aromatic rings

Likewise, Lautens and coworkers have demonstrated the strength of the concept of sequential alkylation-alkenylation by application to the synthesis of fused aromatic rings. Hence, in the presence of 10% of Pd acetate, 20% of tri-2-furylphosphane, two equivalents of norbornene, and two equivalents of cesium carbonate, bromoenoates and related derivatives, ortho-substituted aryl iodides react in boiling acetonitrile in the sense of a Pd-catalyzed ortho-alkylation-intramolecular Heck reaction to furnish fused aromatic carbocy-cles 47-53 in moderate to excellent yields (Scheme 17) [74]. 

LRCOSY experiments for a polynuclear aromatic compound. In the COSY spectrum, cross peaks occur only between ortho neighbors (1,2 and 3,4). In the LRCOSY spectrum, additional cross peaks arise between peri neighbors (5,6 and 4,6). Information on the connectivity between fused aromatic rings thus becomes available in the LRCOSY case. 

Among the many classes of chiral molecules, helical systems are particularly fascinating. Their structure is relevant to proposed mechanisms of handedness induction in relation to chiral amplification [76], Helicenes ([A]-H) are helical molecules formed from A-ortho-fused benzene rings (Fig. 8) which display considerable rotatory power [77]. Helicenes are presently the subject of intense synthesis efforts that try to functionalize these molecules in order to attain enhanced electric, magnetic, and optical properties [78, 79]. Phenylenes ([A]-P), or heliphenes, constitute another class of helical aromatic compounds for which syntheses have recently been reported [80, 81]. They are made up of N benzene rings fused together with N - 1 cyclobutadiene rings (Fig. 8). 

The accepted configuration of naphthalene, ie, two fused benzene rings sharing two common carbon atoms in the ortho position, was estabUshed in 1869 and was based on its oxidation product, phthaUc acid (1). Based on its fused-ring configuration, naphthalene is the first member in a class of aromatic compounds with condensed nuclei. Naphthalene is a resonance hybrid ... 

Shown below are the aromatic ring systems and names of compounds in this book used for Method 1. There are two types of these. The ori/zo-fused and the ortho- and peri-fused rings. For each of the ori/zo-fused ring systems the corresponding saturated ring system and the name obtained by Method 2 is shown. 

Taylor has collected the above and similar data and compared the ratio of reactivities of the ortho and para positions of compounds of type 19 (expressed as log/odog/p) with the ratio of reactivities of the equivalent positions, a and c, in compounds of type 20 and found that the latter ratio was lower, i.e., a relative increase in the reactivity of the para position (c) has occurred upon ring formation. This fall in the ratio log fa log fc increases along the series X = S < 0 (< NH < CHg) in 20. As this trend parallels the increase in strain in the fused bridging ring it was argued that ring strain was the primary cause of the reduction in ratio. Position a is a-aromatic and position c is j8-aromatic therefore the above concept represents an extension by Taylor of an earlier explanation of the Mills-Nixon effect in indane. Further substitution... 

Since these heterocyclic ring systems are not aromatic, they are best considered as substituents on the fused benzene ring, i.e. the reactivity shown by the benzene ring towards electrophiles, for example, will be predictable by considering the heterocyclic ring simply as two ortho substituents. The reactivity will then be a result of the normal electron releasing or withdrawing properties of the substituents. 

Univalent radicals derived from ortho-fused or ortho- and peri-fused polycyclic hydrocarbons with names ending in -ene by removal of a hydrogen atom from an aromatic or alicyclic ring are named in principle by changing the ending -ene of the names of the hydrocarbons to -enyl . 

TTie lithiation of a l,6-methano[10]annulenamide occurs selectively at the peri position, but the lithiation of fused ring aromatics t es place preferentially at the ortho (rather than peri) position,as shown by the examples in Scheme 12. Subsequent transformations of the phthalides obtained in the naphthalene example also illustrate the usefulness of this method for the annelation of aromatic rings. The preference for ortho over peri lithiation holds true for phenanthrenes as well. The selective metd-ation of trimethoxyphenanthrenamide (15) followed by phthalide synthesis as above constitute the key steps in the synthesis of the phenanthroquinolizidine alkaloid cryptopleurine and the phenanthroindoli-zidine alkaloid antofme (Scheme 13). ... 

Heterocyclic compounds bearing a mercapto group ortho to a ring nitrogen react with aromatic cyanate esters (2 mol) to yield fused structures... 

The molecular information that FTIR detection offers that MS, the other common hyphenated GC technique, cannot, includes elucidation of aromatic ring substitution (for example, with di-substitution, ortho, meta, or para), cis or trans or geminal substitution on a carbon-carbon double bond, the arrangement of rings in PAHs (benz[a]anthracene versus chrysene or triphenylene or benzo(c]phenan-threne or tetracene for the four-ring ortho-fused PAHs), aUcyl-chain branching isomers, and alcohols, which often shows in the MS as the easily dehydrated product aUcene [84]. 

Note the use of the prefixes, 0- for ortho-, m- for meta-, and p- for para-, to indicate the 1,2-, 1,3-, and 1,4-disubstituted benzene, respectively. There are many aromatic hydrocarbons with fused benzene rings—rings with 2 C atoms in common —as in naphthalene, CioHg, a white solid (m.p. SOX) used as a moth repellent ... 

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