Practical synthesis of lodo phenothiazines.: A facile access to electrophore building blocks

Bromine-lithium exchange of the mono- and dibromophenothiazines 1 and 3a regiospecifically furnishes upon electrophilic trapping with iodine the iodo- and diiodophenothiazines 2, 3b, and 3d in excellent yield. The 3-bromo-7-iodophenothiazine 3d can be submitted to regio-selective and sequential Suzuki coupling reactions with phenothiazine mono- and hisboronates 4 and 5 and/or (hetero)aryl boronic acids to give the bromodiphenothiazine 6a, the dibromo terphenothiazine 7, and the (hetero)arylsubstituted phenothiazine dyads 6b-d in moderate to good yields.