Ring-chain tautomerism substitution, nucleophilic

Oxazolidines 288 are subject to ring-chain tautomerism. The process can be considered as a reversible intramolecular nucleophilic addition to the C=N bond. A variety of substituted oxazolidines exist in the open-chain form 289 in the solid state <1985T5919, 1992T4979>. In solution, the two forms are in equilibrium, the position of which depends on the solvent and the substituents. 

Quinazolin-4(3//)-ones are not readily degraded by reagents in alkaline media because they form stable anions. However, if the tautomeric hydrogen is substituted, then the heterocyclic ring becomes susceptible to cleavage. Two such examples are 3-propadienylquinazolin-4-one (33) and l-acetyl-2-(a-ethoxy-a-phenyl)benzylquinazolin-4-one (34). When the former compound was boiled for 2 hours with sodium in 96% ethanol, nucleophilic attack at C-2 occurred and 2-(2-formamidophenyl)-5-methyloxazole was formed by a subsequent reaction of the olefinic side chain. The second... 

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