Highlyortho-Selective Chlorination of Anilines Using a Secondary Ammonium Salt Organocatalyst

The Rise of Trichlorides Enabling an Improved Chlorine Technology

Chlorine plays a central role for the industrial production of numerous materials with global relevance. More recently, polychlorides have been evolved from an area of academic interest to a research topic with enormous industrial potential. In this minireview, the value of trichlorides for chlorine storage and chlorination reactions are outlined. Particularly, the inexpensive ionic liquid [NEt₃ Me][Cl₃ ] shows a similar and sometimes even advantageous reactivity compared to chlorine gas, while offering a superior safety profile. Used as a chlorine storage, [NEt₃ Me][Cl₃ ] could help to overcome the current limitations of storing and transporting chlorine in larger quantities. Thus, trichlorides could become a key technique for the flexibilization of the chlorine production enabling an exploitation of renewable, yet fluctuating, electrical energy. As the loaded storage, [NEt₃ Me][Cl₃ ], is a proven chlorination reagent, it could directly be employed for downstream processes, paving the path to a more practical and safer chlorine industry.

Complementary Site-Selective Halogenation of Nitrogen-Containing (Hetero)Aromatics with Superacids

Site-selective functionalization of arenes that is complementary to classical aromatic substitution reactions remains a long-standing quest in organic synthesis. Exploiting the generation of halenium ion through oxidative process and the protonation of the nitrogen containing function in HF/SbF₅ , the chlorination and iodination of classically inert Csp² -H bonds of aromatic amines occurs. Furthermore, the superacid-promoted (poly)protonation of the molecules acts as a protection, favoring the late-stage selective halogenation of natural alkaloids and active pharmaceutical ingredients.

Organocatalytic, Enantioselective Dichlorination of Unfunctionalized Alkenes

The use of a new class of unsymmetrical cinchona-alkaloid-based, phthalazine-bridged organocatalysts enabled the highly enantioselective dichlorination of unfunctionalized alkenes. In combination with the electrophilic chlorinating agent 1,3-dichloro-5,5-dimethylhydantoin (DCDMH) and triethylsilyl chloride (TES-Cl) as the source of nucleophilic chloride, 1-aryl-2-alkyl alkenes were dichlorinated with enantioselectivities of up to 94:6 er. Initial mechanistic investigations suggest that no free chlorine is formed, and by replacement of the chloride by fluoride, enantioselective chlorofluorinations of alkenes are possible.

Efficient Electrocatalysis for the Preparation of (Hetero)aryl Chlorides and Vinyl Chloride with 1,2-Dichloroethane

Although the application of 1,2-dichloroethane (DCE) as a chlorinating reagent in organic synthesis with the concomitant release of vinyl chloride as a useful byproduct is a fantastic idea, it still presents a tremendous challenge and has not yet been achieved because of the harsh dehydrochlorination conditions and the sluggish C-H chlorination process. Here we report a bifunctional electrocatalysis strategy for the catalytic dehydrochlorination of DCE at the cathode simultaneously with anodic oxidative aromatic chlorination using the released HCl as the chloride source for the efficient synthesis of value-added (hetero)aryl chlorides. The mildness and practicality of the protocol was further demonstrated by the efficient late-stage chlorination of bioactive molecules.

Activation of Remote meta-C-H Bonds in Arenes with Tethered Alcohols: A Salicylonitrile Template

Palladium-catalyzed activation of remote meta-C-H bonds in arenes containing tethered alcohols was achieved with high regioselectivity by using a nitrile template. Computational studies on the macrocyclic transition state of the regioselectivity-determining C-H activation steps revealed that both the C-N-Ag angles and gauche comformations of phenyl ether play an extremely important role in the meta selectivity.