Imidazoline analogue

No heterocycle containing a C=N bond is as powerful a director as the oxazolines or tetrazoles described above, but their imidazoline analogues 132 direct well if deprotonated to the amidine equivalent 133 of a secondary amide anion (Scheme 61). Pyrazoles 134 also direct lithiation, but need protecting with a bulky Af-substituent to prevent nucleophilic attack by the base (Scheme 62). ... 

Dantrolene, an imidazoline analogue has been found to possess muscle relaxant characteristics, e.g., Dantrolene Sodium. 

The phosphino-imidazoline catalyst 28 (Fig. 29.15) is a close analogue of the original PHOX ligand. 

A higher analogue of 2-imidazolines, which has recently been examined by nmr (Lloyd et al., 1973) is 2,3-dihydro-lH-l,4-diazepine [80], which protonates on the imino-nitrogen to give cation [81]. Nmr spectra show that this has a half-chair shape, which inverts rapidly at room temperature. 

The one-step synthesis of further tri- and tetracyclic pteridine derivatives from 2-aminopyrazine 153 has also been described <2001JHC1173>. Cyclic analogues of A -[bis(methylthio)methylene]amino reagents such as 2-(methylthio)-2-thiazoline, 5,6-dihydro-2-(methylthio)-4//-l,3-thiazine, 2-(methylthio)-2-imidazoline, 2-(methylthio)-l,4,5,6-tetrahydro-pyrimidine, 2-(methylthio)-2-pyrazine, and 2-chloropyrimidine reacted with aminopyrazine 153 to afford thiazolo/thia-zino[2,3-3]- 159 ( = 1 (53%), n = 2 (42%)), imidazo/pyrimidino[2,l-/ ]- 160 ( = 1 (53%), = 2 (57%)), pyrazino[2,l-/ ]-161 (21%), and pyrimido[2,l-/ ]-pteridine 162 (42%) derivatives, respectively. 

One method used for the control of hypertension is reduction of the impulses flowing from the CNS to the sympathetic nervous system which controls the tone of the cardiovascular system. The veratrum alkaloids do this at doses that are near the emetic dose, and reserpine acts both centrally and peripherally. The imidazoline clonidine (175) and some analogues in which the chlorine is replaced by fluorine or methyl groups decrease sympathetic outflow and cause vasomotor relaxation. However, they cause sedation, lack of saliva and renewed hypertension on withdrawal of the drug. 

The 5-thione analogue of Step 3, l-(3-pyridinylamine-2-thiomethyl-4-methyl-4-phenyl-2-imidazolin-5-thione, (II), and derivatives were previously prepared by the author and are described (1). 

In contrast to the 2,4-dioxoimidazoles (and such compounds as 5-phenyl-2-thiohydan-toin), there is convincing evidence (UV, IR, NMR data) that imidazolidine-2,4-dithiones exist mainly in the thione-thiol forms (84 Scheme 27). The two tautomers (85,86) have been separated in 5,5-diphenylimidazoIidine-2,4-dithione in KBr the C=N bands appear at 1495 and 1575 cm , respectively. In the 5,5-spiropentane analogues the structure related to (85) increases in importance as the solvent polarity increases. As mentioned above, the oxo-thione structures for imidazolin-4-one-thiones is supported by IR spectra in the solid state, and by UV spectra in ethanol. The partially fixed derivatives (87,88 Scheme 28) can be crystallized separately, but give identical spectra in solution. Both X-ray crystal structures and solid state IR spectra confirm the existence of two structures (87 y(C=0) 1690, r(C=N) 1510-1490 cm ) and (88 r(C=0) 1720, r(C=N) 1590-1575 cm ). As with the dithiones, the importance of the cross-conjugated form (88) increases with decrease in solvent polarity. 

In the selection of an appropriate corrosion inhibitor, an important consideration is the problem of adverse competition with other additives designed to adsorb on the liquid-metal interface. Extreme pressure and/or antiwear agents compete for the same sites as the corrosion inhibitor. Eatty amines are good corrosion inhibitors in this type of environment. However, their adverse effect on the performance of ZDDP additives often prohibits their use. Half esters or amides of dodecylsuccinic acid, phosphate esters or thiophosphates are frequently employed. A combination of inhibitors is sometimes used, for example, fatty carboxylic acids or the dimer/trimer analogues of the unsaturated acids, e.g. oleic, used in conjunction with an amine such as an ethanolamine or alkyl amine, or amide such as alkyl imidazoline and sarcosines, Eig. 6.7. Shorter chain carboxylic acid and amines are used as volatile corrosion inhibitors. 

Higher activity of catalysts embodying imidazolin-2-ylidene ligands (e.g., 3u) for RCM has been observed. Such complexes as 3u and 5 allow formation of tetrasubsti-tuted cycloalkenes, and various functionalized analogues (e.g., 1-cyanoalkenes ). The highly active catalyst 9 is recoverable and recyclable. ... 

The antihypertensive imidazoline clonidine (Fig. 19.7 Ri = R2 = Cl) and its analogues activate norepinephrine, as well as specific receptors of the central nervous system. The maximal activity in this series is always observed when both... 

Cyclic basic-chain analogues essentially having (a) Imidazoline,... 

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