Nitrogen heterocycles reactions with acetylenic esters

III. Reactions of Acetylenic Acids and Esters with Individual Nitrogen-Containing Heterocyclic Compounds... 

The recently reported (757) conversion of 5-pyrazolones directly to a,j8-acetylenic esters by treatment with TTN in methanol appears to be an example of thallation of a heterocyclic enamine the suggested mechanism involves initial electrophilic thallation of the 3-pyrazolin-5-one tautomer of the 5-pyrazolone to give an intermediate organothallium compound which undergoes a subsequent oxidation by a second equivalent of TTN to give a diazacyclopentadienone. Solvolysis by methanol, with concomitant elimination of nitrogen and thallium(I), yields the a,)S-acetylenic ester in excellent (78-95%) yield (Scheme 35). Since 5-pyrazolones may be prepared in quantitative yield by the reaction of /3-keto esters with hydrazine (168), this conversion represents in a formal sense the dehydration of /3-keto esters. In fact, the direct conversion of /3-keto esters to a,jS-acetylenic esters without isolation of the intermediate 5-pyrazolones can be achieved by treatment in methanol solution first with hydrazine and then with TTN. 

Reactions between nitrogen-containing heterocycles and acetylenic esters often lead to complex mixtures, which may require chromatography and great experimental skill for successful resolution. The products sometimes depend on the precise conditions employed, and on the purity of the reactants or solvents. The choice of solvent can be important. Thus ether and tetrahydrofuran give different results for the combination of DM AD with 1-methylbenzotriazole. The products obtainable from indoles and quinazolines are particularly dependent on the reaction conditions and purity of the solvent. 

Acetylenecarboxylic esters, reactions with nitrogen-containing heterocycles, 23, 263 Acetylenic derivatives of pyrazoles, synthesis and properties of, 82, 1 Acetylenic esters, synthesis of heterocycles through nucleophilic additions to, 19,297 Acid-catalyzed polymerization of pyrroles and indoles, 2, 287... 

Reactions of Acetylene Carboxylic Esters with Nitrogen Heterocycles... 

Acheson, R. M., Reactions of Acetylene-carboxylic Acids and Their Esters with Nitrogen-Containing Heterocyclic Compounds, 1, 125. 

---