Uncatalyzed side-chain halogenations of polymethyl-substituted thiophenes take place cleanly and regioselectively at the α-position. Thus, for example, treatment of tetramethylthiophene with 1 equiv of bromine in CCl4 at −18 °C affords 2-bromomethyl-3,4,5-trimethylthiophene in 76% isolated yield, while the use of 2 equiv of bromine produces 2,5-bis(bromomethyl)-3,4-dimethylthiophene nearly quantitatively
聚甲基取代的
噻吩的未催化侧链卤化反应在α位置干净且区域选择性地发生。因此,例如,在-18°C下在CCl 4中用1当量的
溴处理四甲基
噻吩,可得到76%分离产率的2-
溴甲基-3,4,5-三甲基
噻吩,而使用2当量的
溴可产生2, 5-双(
溴甲基)-
3,4-二甲基噻吩几乎是定量的。