Practical synthesis of iodo 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 regioselective and sequential Suzuki coupling reactions with phenothiazine mono- and bisboronates 4 and 5 and/or (hetero)aryl boronic acids to give the bromodiphenothiazine 6a, the dibromo terphenothiazine 7, and the (hetero)aryl-substituted phenothiazine dyads 6b-d in moderate to good yields.