First example of base-promoted tandem alkylation-bromination of 2-bromothiophene via halogen dance process: a remarkable temperature effect

Metalation-alkylation of 2-bromothiophene 1 when conducted at low temperature led to the 5-alkylated 2-bromo products 2. While, at room temperature, the same sequential reactions afforded the original dibromo-alkylated thiophenes 3 following an unprecedented halogen transfer-based halogen dance process in highly regiocontrolled and ordered way.