Use of the Ullmann Reaction for the Synthesis of Heterocyclic Compounds
Nagler, Lisa A.
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3,4,5-Tribromo-N,N,a-trimethylpyrazole -acetamide (1) and 3,4,5-Tribromo-l-methylpyrazole (9) reacted with copper powder to give the 5,5 -bipyrazoles (2) and (15), respectively. Attempts to dimerize the ethyl ester of 3,4,5-tribromopyrazole-l-acetic acid (l0) gave the dibromo ester (18) as the major reaction product. The related l-substituted-2,4,5-tribromoimidazoles (4a) and (4b) dimerized to give 2,2 1 -biimidazoles while 4,S-dibromo-N, N,a-trimethylimidazole-l-acetamide did not react with copper powder. Attempts to cyclize the bipyrazoles (6) and (23) to tricyclic products were unsuccessful.