Effects of tertiary amine catalysis on the regioselectivity of anisole chlorination with trichloroisocyanuric acid

Mild Aliphatic and Benzylic Hydrocarbon C-H Bond Chlorination Using Trichloroisocyanuric Acid

We present the controlled monochlorination of aliphatic and benzylic hydrocarbons with only 1 equiv of substrate at 25-30 °C using N-hydroxyphthalimide (NHPI) as radical initiator and commercially available trichloroisocyanuric acid (TCCA) as the chlorine source. Catalytic amounts of CBr₄ reduced the reaction times considerably due to the formation of chain-carrying ·CBr₃ radicals. Benzylic C-H chlorination affords moderate to good yields for arenes carrying electron-withdrawing (50-85%) or weakly electron-donating groups (31-73%); cyclic aliphatic substrates provide low yields (24-38%). The products could be synthesized on a gram scale followed by simple purification via distillation. We report the first direct side-chain chlorination of 3-methylbenzoate affording methyl 3-(chloromethyl)benzoate, which is an important building block for the synthesis of vasodilator taprostene.

Selective di- and monochlorination of pyridazine-annelated bis(imidazolium) salts

A synthetic route for the selective di- and monochlorination of pyridazine annelated bis(imidazolium) salts at the formamidinium moieties with trichloroisocyanuric acid (TCCA) is presented. Due to the steric hindrance, the molecular structure of the dichlorobis(imidazolium) salt shows a pronounced torsion from planarity as well as a deviation of the C–Cl bond vectors from the ideal bisecting line of the respective NCN angles such as to avoid each other. The monochlorinated bis(imidazolium) salt is free of steric hindrance and therefore shows less deviation from the parent bis(imidazolium) salt. In the presence of acetate the chloroimidazolium salt acts as a chlorination agent for acetate leading to formation of acetyl chloride and the respective urea.