Reaction of 2,4-dinitrobenzenediazonium ions with thiophens. Part 2. Coupling reactions, involving unexpected reactions with electron-rich methyl groups in addition to the expected ring attack

Abstract

2,4-Dinitrobenzenediazonium ions couple with 2-phenylthiophen, 2-t-butylthiophen, 2,4-dimethylthiophen, and 2-methyl- and 3-methyl-benzo[b]thiophen to give the expected dinitrophenylazothiophens. 2,5-Dimethylthiophen yields in addition to the 3-(2,4-dinitrophenylazo)thiophen an almost equal proportion of the 2,4-dinitrophenylhydrazone of 5-methylthiophen-2-carbaldehyde. 2,3,5-Trimethylthiophen and tetramethylthiophen, treated with the diazonium salt, give exclusively the 2,4-dinitrophenylhydrazone formed by coupling with the α-methyl group. 2,3-Dimethylbenzo[b]thiophen does not react.