Two Fused Six-Membered Rings

When two fused six-membered rings (naphthalene analogues) are considered, possibilities become very numerous, partly on account of the reduced symmetry of naphthalene, compared with benzene, and also because of the larger number of positions available for substitution. Thus, there are two monoazanaphthalenes, quinoline (8) and isoquinoline (9), four benzodiazines [cinnoline (10), phthalazine (11), quinazoline (12) and quinoxaline(13)], with the two nitrogen atoms in the same ring, and six naphthyridines (e.g. (14), named and... 

From the satellites in the ESR spectra, the symmetry of the radicals as well as the information about the localization of the unpaired electron in RGgp can be obtained (Figure 6.2). In BuGgQ, for example, ten pairs of G satellites are clearly resolved (Figure 6.1). A Q-symmetry can be deduced from their relative intensities and splittings [1, 12]. The unpaired electron is mostly located on two fused six-membered rings of the Gjq surface, which rules out an extensive delocalization on the Ggo framework. 

TWO FUSED SIX-MEMBERED RINGS 15.3.1. Compounds Related to Methotrexate... 

The bicyclic compound decahydronaphthalene, or bicyclo[4.4.0]decane, has two fused six-membered rings. It exists in cis and trans forms (see Figure 1.11), as determined by the configurations at the bridgehead carbon atoms. Both cis- and trans-decahydronaphthalene can be constructed with two chair conformations. 

This sequence serves to exemplify the formation and aspects of reactivity of toluene-p-sulphonate esters in monosaccharide systems, and further to illustrate the selective protection afforded to hydroxyl groups by the formation of cyclic acetals by reaction with carbonyl compounds. Thus reaction of methyl a-D-glucopyranoside (26) with benzaldehyde in the presence of zinc chloride gives the 4,6-acetal (27) (Expt 5.118), wherein two fused six-membered rings of the frans-decalin type are present. As a cognate preparation the reaction of benzaldehyde with methyl a-D-galactopyranoside results in a similar conversion to a 4,6-acetal, but in this case the product is the conformationally flexible system of the cis-decalin type, the most likely conformation being that shown below. 

Decalin (Section 29.8A) Two fused six-membered rings. ci.v-Decalin has the hydrogen atoms at the ring fusion on the same side of the rings, and frans-decalin has the hydrogen atoms at the ring fusion on opposite sides of the rings. 

This is an unusual case of two vicinal five-membered rings being converted into two fused six-membered rings, without further alterations of other functional groups on the molecule, notably nitrile. This means that water must have been rigorously excluded to prevent the hydrolysis of this function to amide or carboxylic acid, since the reaction medium is strongly acidic. 

X-ray structural analysis shows that the two fused six-membered rings in pteridine (pyrazino[2,3 /]pyrimidine) are virtually coplanar. Its C-C and C-N bond lengths and C-N-C bond angles (with values less than 120°) are comparable to those of pyrimidine and pyrazine (see Fig. 6.23) ... 

Soon after its availability, 50 was subjected to reaction with benzyne. A series of adducts with the formulas [C60 + (C6H4) ], where n - 1, was detected by mass spectrometry . The monoadduct was isolated via high performance liquid chromatography and characterized by its and NMR spectra . These data show that benzyne adds across the pyracyclene bond (i.e. across the bond between two fused six-membered rings, as shown in 432). Consequently the NMR spectrum appears as an AA BB multiplet for the benzenoid ring protons, and the spectrum shows 19 of 20 peaks expected for the symmetry of 432. 

Systematic studies have shown the importance of each part of the drug for effectiveness. It has been found, for example, that the carboxylate anion (— C00 ) is essential, as are both the 3-OH and 5-OH groups. It has also been shown that almost any modification of the two fused six-membered rings and their pattern of substitution reduced potency. 

The aconitine-type alkaloid (96) is most probably formed from the atisine skeleton through different modifications as indicated in Scheme 28.4. The intermediate 94 after a Wagner-Meerwein rearrangement process converts two fused six-membered rings into a (7 -i- 5)-membered bicyclic system in which C-17 exocyclic... 

Decalin is a bicyclic system composed of two fused six-membered rings. The smictures of c -decalin and tram-decdin are as follows ... 

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