Ring systems polycyclic compounds

Intramolecular reactions between donor and acceptor centres in fused ring systems provide a general route to bridged polycyclic systems. The cts-decalone mesylate given below contains two d -centres adjacent to the carbonyl function and one a -centre. Treatment of this compound with base leads to reversible enolate formation, and the C-3 carbanion substitutes the mesylate on C-7 (J. Gauthier, 1967 A. Belanger, 1968). 

Various bicyclic and polycyclic compounds are produced by intramolecular reactions] 127]. In the syntheses of the decalin systems 157 [38] and 158 [128], cis ring Junctions are selectively generated. In the formation of 158, allyhc silyl ether remains intact. A bridged bicyclo[3.3. l]nonane ring 159 was constructed... 

Polyaza six-membered ring systems, 3, 1039-1086 Poly-e-caprolactone production, 7, 589 Polycyclic compounds nomenclature, 1, 14-28 Polyfuroxans, 6, 426 Polygermacyclopentanes, 1, 609... 

Guanacastepene A (444) is a novel tricyclic diterpene with fused five-, seven-, and six-membered rings. The possibility of constructing polycyclic compounds via tandem RCM of dienynes was used in Hanna s synthesis of a highly functionalized tricyclic system 443 related to 444. Under the conditions outlined in Scheme 87, trienyne 440 provided the desired tricycle 442 in a single step, as a result of sequential enyne RCM followed by RCM of intermediate 441. Compound 442 was then further functionalized to 443 [182]. 

Strategies based on two consecutive specific reactions or the so-called "tandem methodologies" very useful for the synthesis of polycyclic compounds. Classical examples of such a strategy are the "Robinson annulation" which involves the "tandem Michael/aldol condensation" [32] and the "tandem cyclobutene electrocyclic opening/Diels-Alder addition" [33] so useful in the synthesis of steroids. To cite a few new methodologies developed more recently we may refer to the stereoselective "tandem Mannich/Michael reaction" for the synthesis of piperidine alkaloids [34], the "tandem cycloaddition/radical cyclisation" [35] which allows a quick assembly of a variety of ring systems in a completely intramolecular manner or the "tandem anionic cyclisation approach" of polycarbocyclic compounds [36]. 

Although many hydrocarbons exhibit fluorescence, often they are colourless and the fluorescence is only just into the blue, e.g. the linear terphenyl and quaterphenyl. Polycyclic ring systems such as terrylene and rubicene are used in analytical methods and OLEDs but a large number are ruled out of commercial use because of their potential to act as carcinogens. However, as mentioned in section 3.5.1.3, pery-lene is a useful fluorophore in a variety of outlets and pyrene is another polycyclic compound of interest. One derivative of pyrene (3.27) is a yellow-green fluorescent dye used in textile applications (Cl Solvent Green 7) and in analysis and sensors (see section 3.5.6.4). 

When phosphaalkynes are exposed to bis- and tris(diazo) compounds, bis- or tris(l,2,4-diazaphosphol-5-yl) compounds are formed that may be further converted into a variety of novel heterocyclic systems. For example, bis- and tris[diazo(tri-methylsilyl)methyl]phosphanes 237 and 240 afforded bis- and tris(diazaphospho-lyl)phosphanes 238 and 241 after cycloaddition with terf-butylphosphaacetylene followed by a subsequent 1,5-silyl shift (Scheme 8.56) (300). Reaction with electrophilic halides at the Wsilyl functions allows the introduction of a heteroatom bridge between the diazaphosphole ring leading to polycyclic ring systems such as 239 and 242. 

It is necessary to differentiate between reactions where the two identical moieties undergoing photocyclodimerization, i.e. the chromophores, are part of the same molecule (such reactions are formally photoisomerizations with coincident ring formation) on the one hand and intermolecular photocyclodimerizations on the other. The former reactions, which will be treated first, can occur in molecules where the two (identical) moieties are linked together by a simple chain (to afford polycyclic systems), or by a ring system (to afford cage compounds). 

V-aryl-o-haloanilines can be converted into indole derivatives in a palladium catalysed oxidative addition, C-H activation sequence. The transformation has been utilized extensively in the preparation of polycyclic compounds. In a recent example, leading to the formation of the carbazole ring system, Larock and co-workers demonstrated that the formation of the... 

Coke-oven tar is an extremely complex mixture, the main components of which are aromatic hydrocarbons ranging from the monocyclics benzene and alkylbenzenes to polycyclic compounds containing as many as twenty or more rings. Heterocyclic compounds containing oxygen, nitrogen, and sulfur, but usually only one heteroatom per ring system are present. Small amounts of paraffinic, olefinic, and partly saturated aromatic compounds also occur. 

However, Aae can still be used in suitable cases as an indication of conformation, particularly for polycyclic compounds. Thus Aae measurements on TV-CH2X protons may be used to establish the cis or trans nature of the ring fusion in 1,3-heterocyclic systems. For example, the trans-fused perhydro-pyrido[3,2,l-iJ][3,l]benzoxazine (21) shows Aae 0.84 ppm, indicative of the anti-coplanar CH-nitrogen lone-pair geometry, whereas the cis-fused isomer (22), in which the nitrogen lone pair bisects the CH2 group, shows Aae 0.12 ppm.45... 

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