Pseudo-base formation

It is interesting that only mono- and not di-pseudo bases are obtained, and that with 1,6-naphthyridine, pseudo base formation occurs at the quinolinoid site, the diquatemary salt (79) yielding (80) and not (81). However naphthyridinediones are formed on reaction with alkaline K3Fe(CN)6 (72CJC917, 74CJC962). 

Although the polypyridyl ligands are reported to be quite stable after coordination, covalent hydration and pseudo-base formation have been reported, although not proved unequivocally.134... 

Here, the ylid form can be stabilized by enolate formation and by d-orbital resonance, which explains the moderate value of pK. The possibility of pseudo-base formation can be excluded (75) by comparison with u.v. spectra. Thus, polarography made it possible to detect and characterize stable ylid formation in solutions several years before these ylids were isolated. 

Substituent effects on rates and equilibria in hydride transfers between a range of NAD+ analogues have been examined. Anhydrous and aqueous acetonitrile and aqueous isopropyl alcohol have been used as reaction media, and earlier caveats as to possible complicating kinetic effects of nonproductive adduct formation apply, particularly where hydroxylic solvents are used. Data from hydride transfers have been compared with equilibria, kR +, and rates for pseudo-base formation, or for formation of cyanide adducts. The aqueous alcoholic solvent has an added disadvantage that p/fR+-values for the cations are necessarily composite. 

Katritzky and co-workers reported the pseudo-base formation of 208 and its derivatives by using H-NMR spectra. Spectra of DMSO-d6 samples are sensitive to the presence of water and an up-field shift was observed. They suggested covalent hydration at position 2 (830MR649). 

A few new Reissert compounds have been made by the aqueous method, but the vast majority by the methylene chloride-water solvent system. A new variation of the latter method, which is particularly useful in cases where pseudo-base formation becomes a problem, - adds a small quantity of benzyltrialkylammonium chloride to the reaction mixture. " The phase transfer agent appears to enhance the transport of the cyanide ion to the methylene chloride phase. 

Most activity in this area has centered around the isolation of so-called pseudo-bases (82) in which the cyano group is replaced by a hydroxy group. Thus the pseudo-base is obtained, in addition to the normal Reissert compound, from S-nitroisoquinoline, " 3-methyl-5-nitroisoquinoline, 6-nitroquinoline, and phthalazine. Heating the pseudo-bases in alcohol gives rise to the ethers 83. A discussion of some of the chemistry and properties of the pseudo-bases has appeared. The formation of the pseudo-bases can be suppressed and that of the Reissert compounds increased by the use of a phase-transfer catalyst. Pseudo-bases have also been obtained in attempts to form Reissert compounds from 1,6-naphthyridine and 4,6-phenanthroline. 2-Phenyl-1,2,3-thiadiazole and benzoyl chloride in the presence of cyanide gave 84 and imidazo[l,5-a]pyrazines with acid chloride gave 85 in reactions analogous to the pseudo-base formation. 

In yet a further application of equilibrium data, the AH° for pseudo-base formation of isoquinolinium methiodide has been compared with corresponding data for 3,4-dihydroisoquinolinium methiodide, leading to a value of 48 9 kcal mole-1 for the ERE of the former.50... 

Determinations of the ERE of quinoline from thermochemical data have given results which range from 47.3 to 69 kcal mole-1.49-271-272 There appear to be no corresponding estimates for isoquinoline, but a value of 48 9 kcal mole-1 has recently been deduced from a comparison of the equilibrium constants for pseudo-base formation of iV-methylisoquinoline cation and its dihydro analog 73.273 Comparison of these ERE values with those obtained for naphthalene (61-75 kcal mole-1) shows that they parallel the somewhat lower resonance energy of pyridine relative to that of benzene. 

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