Purification of Laboratory Chemicals
- D. D. Perrin, W.L.F. Armarego
The reaction of isoxazol-5(2H)-ones, unsubstituted at C-3, with base is well known and the various intermediates have been trapped to prepare a large number of hetrocyclic system. However, the reaction of 3-substituted compounds with base is not so well known, and the only reported reactions appear to be that described by Doleschall, who alkylated the anion of ethyl 2,3-dimethyl-2,5-dihydro-5-oxo-isoxazole4-carboxylate, in order to obtain γ-alkylated acetoacetates. In previous studies we have shown that the products obtained from the reaction of certain 2-aryl-3-arylaminoisoxazolones 1, substituted on nitrogen with an isoquinoline or quinazoline group, react with triethylamine to give imidazoisoquinoline 2 and imidazoquinazolines 3 respectively. When the N-substituent is a nitropyridine, 2-aminoindole derivatives 4 are formed instead, and 2pyridyl-3-(3-substituted phenyl)aminoisoxazol-5(2H)ones 5 react with triethylamine to form the corresponding imidazo[1,2-a]pyridines 6, an outcome that is formally the same as that achieved by photolysis or pyrolysis. We have also reported that 3-arylamino-4-ethoxycarbonylisoxazol-5(2H)-ones, substituted on nitrogen with a benzothiazole group, react with triethylamine to provide a convenient synthesis of ethyl 2-arylaminoimidazo[2,1b]benzothiazole-3-carboxylates (Scheme 1).