Pseudo-bases oxidation

With W-substituted quaternary derivatives in the presence of oxidizing agents, ring opening is avoided and the classical Dekker oxidation of the pseudo-base occurs to give (45) (62JCS1671). 

Oxidation to an azolone is an expected reaction for a pseudo base, but little appears to be known of such reactions. Most commonly, pseudo bases suffer ring fission. Estimated rates of ring-opening of (169) are in the ratio 10 10" 1 for X = O, S and NMe, respectively (79AHC(25)1). 

Diazinium salts resemble pyridinium salts in their behavior. They form pseudo-bases with hydroxide ions which can disproportionate (e.g. 2-methylphthalazinium ion (199) — 2-methylphthalaz-l-one + 2-methyl-l,2-dihydrophthalazine) or undergo ring fission (e.g. 3-methylquinazolinium ion — (200). Aqueous acid converts (201) into (202), presumably by attack of a water molecule on a protonated species with subsequent intramolecular oxidative-reductive rearrangement of an intermediate carbinol base (201a) as shown. 

Some pseudo-bases do not ring open the xanthylium ion (210) gives xanthydrol (211) which can be isolated or oxidized with dilute nitric acid to xanthone (212). 

Dihydroisoquinolines, e.g. (484), are basic and form quaternary salts, e.g. (521). With alkali these salts form carbinolamine pseudo-bases, e.g. cotamine (522 Y = OH), which can be oxidized to lactams or which disproportionate on standing. The quaternary ions can also react with other nucleophilic reagents, e.g. (521) + RMgBr — (522 Y = R) (521) + MeCOMe — (522 Y = CH2COMe) (521) + CN — (522 Y = CN) (521) + RNH2 —+ (522 Y = NHR). The pseudo-bases are in equilibrium with open-chain compounds since aldehyde derivatives can be prepared. 

Oxidative-reductive disproportionation is a rather typical property of some pseudo bases. Thus, l,3-dimethyl-2-hydroxybenzimidazoline (229), which exists in the solid state in the open-chain form (228), on heating at 165-185°C, is converted to mixture of 1,3-dimethylbenzimidazolone (230) (49%) and 1,3-dimethylbenzimidazoline (231) (46%) (85KGS1694). Evidently, the process proceeds via an equilibrium amount of (229) undergoing hydride transfer. 

Oxidation to an azolone is an expected reaction for a pseudo base, but little appears to be known of such reactions. Most commonly, pseudo bases suffer ring fission. Estimated rates of ring opening of 246 are in the ratio 109 104 5 1 for X = 0, S, and NMe, respectively. Thiazolium salts 247 consume two equivalents of OH on titration because the pseudo bases 248 lose a proton to give 249, which then form anions 250. Quaternized oxazoles 251 are readily attacked by hydroxide to give open-chain products such as 252, and quaternized 1,3,4-oxadiazoles behave similarly. Quaternary isothiazoles (e.g., 253) are cleaved by hydroxide, as are 1,2,4-thiadiazolium salts (254 255). 

This and other evidence (16) indicated that eseretholemethine (VI R = C2H5) was a pseudo base or carbinol amine. Thus, on oxidation with silver nitrate an oxindole was obtained (dehydroeseretholemethine, VII R = C2H5), which on subsequent Hofmann degradation and reduction of the Hofmann elimination product gave 5-ethoxy-l,3-dimethyl-3-ethyloxindole (13). The methyl homolog (VII R = CHa),... 

Grapes, wine and other berry products are acidic, and the anthocyanins are in the flavylium form. A hypothesis that the anthocyanins may be pH-transformed into their carbinol pseudo-base and quinoidal base, or the chalcone, in the intestine and blood system during digestion has been proposed by Lapidot et al. (1999). These compounds have been shown to have antioxidant activity and are also most likely absorbed from the gut into the blood system. The pseudo-base and the quinoidal base of malvidin and malvidin-3-glucoside remained as very effective antioxidants, both when tested by a linoleate-oxidizing assay and by a microsomal lipid peroxidation assay. 

Quinoline 1-oxide can be substituted by mercaptans with the 3-isomer being the major product.Heterocyclic acid amides, such as lO-methyl-9-acridone and 2-methyl-l-phthala-zone, were aminoalkylated by ClMg(CHa)sNMe3. The carbinols formed have the character of pseudo bases and were transformed to the corresponding acridinium or phthalazinium salts. ... 

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