Two-ring systems

All of these effects can be accounted for by extensions of an additivity scheme, when special increments are attributed to monocyclic structures and the combination of two ring systems having one, two, or three atoms in common [23]. Combination of a table containing values for these ring fragments with an algorithm for the determination of the smallest set of smallest rings (SSSR) [24] (see also Section 2.5.1) allows such a procedure to be performed automatically. 

Radicofunctional nomenclature can be used when a carbonyl group is attached directly to carbon atoms in two ring systems and no other substituent is present having priority for citation. 

A kinetic study of the mercuric acetate oxidation of l-alkyl-3,5-dimethyl-piperidines (81) and 3-alkyl-3-azabicyclo[3.3.1]nonanes (82) was made to evaluate the effect of the N-alkyl group on the rate of oxidation and to contrast these two ring systems (70). The maximum factor in the piperidine... 

Two ring systems derived from pyrazole have been studied more recently. The 4 -pyrazole ring (25) forms quaternary salts (26) with fair ease, and, as in the case of pyridazine (see Section IV, C), the direction of quatemization is controlled by the nature of R and... 

The fusion of four membered-heterocycles with two heteroatoms onto face a of the quinoline offers two isomeric combinations of the tricyclic ring system l,2-heterocyclo[2,3-a]quinoline and l,3-heterocyclo[3,2-a]quinoline. The later one of these two ring systems is the only one that examples of it namely, l,3-thiazeto[3,2-a]quinoline have been reported. Moreover, examples of those fused on faces ij or j are not known (Fig. 3). 

Disconnection of the ether linkage (4a) between the two ring systems breaks the molecule into two sizeable fragments. 

The fusion of a pyrimidine ring on face e of the triazine leads to two isomeric ring systems where the site of fusion is [4,5-e] or [5,4-e]. The latter ring system includes some antibiotics, as will be shown later. Consequently, the former ring system stimulated interest in the analogues of the antibiotics. A review article that included these two ring systems appeared recently [92HC(24)261],... 

Wentrup and co-workers have carried out systematic flash vacuum thermolysis studies with a series of fused tetrazoles. Investigations of the isomeric tetrazolo[l,5- ]pyrazine 17 and tetrazolo[l,5-f]pyrimidine 20 showed that, in both cases, ring contraction takes place to afford imidazoles in high yields, but isotope labeling experiments revealed that the mechanisms of the openings of the two ring systems are different <2002JOC8538>. 

In the study of 8, one problem remains. In species like 3 and 5, the ring systems are not planar, thus the two ring systems can t interact through resonance. If the substituent R is to affect the antiaromaticity of the fluorenyl ring system, how is the effect transmitted to the ring system ... 

Little recent clinical data on the potent 2-benzylbenzimidazoles developed by Ciba [170] have been reported, probably because of their pronounced side-effects and addiction liabilities, but a number of chemical and pharmacological studies have been made. Activity is retained when the methylene group linking the two ring systems of the most potent 2-benzylbenzimidazole derivative (LVl) (1 000 X morphine in mice) is altered to NH [171] or CH2O [172], but... 

Simultaneous formation of a two-ring system from acyclic intermediates has also been reported. For example, the reaction of carbonyl-stabilized sulfur ylides with nitrile imines afforded furo[3,2-c]pyrazoles (69TL853). 

A ftptro compound contains a carbon aiorn that is common tc two ring systems,... 

Different results were obtained for 7b. Here steric hindrance causes the two ring systems to be twisted 60° out the common plane. The C-P-C bond angle is only 100,4°, the P-C bond lengths are no longer identical and both are longer than in 6b. To our knowledge, no comparable data on methin- or azamethin-cyanines have been reported (Fig. 4 and 5). 

The nicotine molecule consists of a pyrrolidine ring attached to a pyridine ring by a bond between carbon atoms in the two-ring systems. Nicotine was isolated in impure form from tobacco in 1809 by Louis Nicholas-Vauquelin (1763—1829). Vauquelin called the substance nicotianine. In 1826, Wilhelm Posselt (1806-1877) and Karl Ludwig Reimann (1804-1872), medical students at Heidelberg University, isolated pure nicotine and published dissertations on its pharmacology in 1828. Louis Henri Melsens (1814—1886) determined nicotines empirical formula. Ame Pictet (1857-1937) and P. Crepieux reported the synthesis of nicotine in 1903. 

EXTENSIONS AND COMMENTARY There are three pyrrolidine amines in this tryptamine compilation, and all three are simply weird and illogical. Both the simple "pyrrolidyl tryptamine" (pyr-T) and the 5-methoxy counterpart (5-MeO-pyr-T) caused physical distress, and this one (4-HO-pyr-T) seems to be a more of a stimulant rather than a psychedelic. In all three cases (and with the 5,6-methylenedioxy example as well) the other two ring systems that often accompany the pyrrolide example as a "set" were simply not explored. This is due, largely, to the unexpected and generally negative responses to the pyrrolidine archetype. The piperidine homologue (4-HO-pip-T) is a white crystalline solid with a mp of 180-181 °C. The morpholine analogue is also a white crystalline solid with a mp of 177-178 °C. 

As may be expected from the isosteric relationship between the two ring-systems, 1,2,4-thiadiazoles and the corresponding pyrimidine derivatives show certain similarities in their physical properties. Thus, the boiling points of the parent compounds are strikingly similar5 (see Table V). 

The PMR spectrum of 85a agrees well with theoretical considerations. It can be seen from the vicinal coupling constants that the seven-membered ring is planar, containing localized bonds. A paratropic effect of 1.7 ppm in the five- and six-membered rings and one of at least 2.7 ppm in the seven-membered ring follows from comparison with suitable reference compounds. The different paratropism can be explained by the superposition of two ring systems, a diatropic indolizine and a paratropic [ 12]annulene moiety.106,107... 

The second approach is more rigorous here the p-values are taken as equivalent to that in benzenoid compounds and cr-values are calculated for the thiophene substituents. The calculation may take into account the differing geometries of the two ring systems (use of the Dewar-Grisdale equation). 

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