5-ethyl-7-methyl derivative, degradation

Quaternary salt formation in 4-quinazoline 3-oxide and its 4-amino and 4-methyl derivatives has been studied by Adachi. These N-oxides, prepared by reaction of the simple quinazoline with hydroxylamine, react with ethyl iodide at N-1, although only in the case of the 4-amino derivative could the ethiodide be purified. The salts are degraded by alkali yielding derivatives of ethylaniline [Eq. (4)]. 

Among the volatile compounds listed in Table II, only thiazole compounds are derived from the thermal degradation of thiamin. 5-(2-hydroxyethyl)-4-methylthiazole and 4-methyl-5-vinylthiazoIe are well-known thermal degradation products of thiamin. 5-(2-Chloro-ethyl)-4-methylthiazole may form through the interaction of 5-(2-hydroxyethyl)-4-methylthiazole with hydrogen chloride. However, the most abundant product, 4-methylthiazole, has never been identified as a decomposition product of thiamin. The mechanism for its formation is not clear. 

A-Methylcodonocarpine (105) was transformed to derivative 107 by reduction with H2-Raney nickel, followed by O-ethylation with diazoethane (see Scheme 16). Compound 107 did not give the expected Hofmann degradation product, but rather the ring-closed pyrrolidine derivative 108 after transformation to the quaternary hydroxide followed by pyrolysis. After repeating the methylation and pyrolysis of the quaternary hydroxide followed by catalytic hydrogenation, compound 109 was obtained (95). The degradation product 109 has been synthesized according to Scheme 17 (96). 

Fig. 4. (a) Degradation of anthramycin-11-methyl ether (25) and tomaymycin ethyl ether (28) to anthranilic acid derivatives (28). (b) Formation of the trioxo compound (33) by degradation of tomaymycin (12) and by total synthesis (26). 

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