A selective and direct synthesis of 2-bromo-4-alkylthiophenes: Convenient and straightforward approaches for the synthesis of head-to-tail (HT) and tail-to-tail (TT) dihexyl-2,2′-bithiophenes

A clean and selective method for the synthesis of 2-bromo-4-alkylthiophenes (5a-c) was developed, and the desired products were obtained in excellent yields (>90%). The proposed methodology was based on the regioselective lithiation of 3-alkylthiophenes (1a-c) with n-BuLi at −78 °C and the reaction of the lithiated intermediate with bromine. A simple and efficient protocol for the synthesis of dihexyl-2,2′-bithiophenes from 2-bromo-4-hexylthiophene (5b) was developed via Kumada and Suzuki cross-coupling reactions in high yields (>90%) and excellent selectivity for the head-to-tail (HT) and tail-to-tail (TT) regioisomers.