Radical Mediated C–H Functionalization of 3,6-Dichloropyridazine: Efficient Access to Novel Tetrahydropyridopyridazines

Selective and Stepwise Functionalization of the Pyridazine Scaffold by Using Thio-Substituted Pyridazine Building Blocks

We described a regioselective tri- and tetra-functionalization of the pyridazine scaffold using two readily available building blocks: 3-alkylthio-6-chloropyridazine and 3,4-bis(methylthio)-6-chloropyridazine by performing selective metalations with TMPMgCl ⋅ LiCl and catalyst-tuned cross-coupling reactions with arylzinc halides. Several of the resulting pyridazines were converted into more elaborated N-heterocycles such as thieno[2,3-c]pyridazines and 1H-pyrazolo[3,4-c]pyridazines.

Hydrogen Atom Transfer Driven Enantioselective Minisci Reaction of Alcohols

Catalytic enantioselective Minisci reactions have recently been developed but all instances so far utilize α-amino radical coupling partners. We report a substantial evolution of the enantioselective Minisci reaction that enables α-hydroxy radicals to be used, providing valuable enantioenriched secondary alcohol products. This is achieved through the direct oxidative coupling of two C-H bonds on simple alcohol and pyridine partners through a hydrogen atom transfer (HAT)-driven approach: a challenging process to achieve due to the numerous side reactions that can occur. Our approach is highly regioselective as well as highly enantioselective. Dicumyl peroxide, upon irradiation with 390 nm light, serves as both HAT reagent and oxidant whilst selectivity is controlled by use of a chiral phosphoric acid catalyst. Computational and experimental evidence provide mechanistic insight as to the origin of selectivity, revealing a stereodetermining deprotonation step distinct from the analogous reaction of amide-containing substrates.

Free-Radical-Promoted Dehydrogenative Coupling of Polyfluorinated Alcohol with Quinone, Chromone, and Coumarin

A free-radical-mediated dehydrogenative cross-coupling reaction of polyfluorinated alcohol with quinone, coumarin, and chromone was developed. It provides a sustainable and practical strategy for installation of fluorine atom into organic molecules by using polyfluorinated alcohols.

Synthesis of Substituted 6,7-Dihydro-5H-pyrrolo[2,3-c]pyridazines/pyrazines via Catalyst-Free Tandem Hydroamination-Aromatic Substitution

Herein, we report an efficient and operationally simple synthesis of 6,7-dihydro-5H-pyrrolo[2,3-c]pyridazines and 6,7-dihydro-5H-pyrrolo[2,3-b]pyrazines via a tandem hydroamination-S_NAr sequence that makes use of mild reagents under catalyst-free conditions in moderate to high yields. This chemistry expands the known scope of pyridazine/pyrazine chemistry and can be applied toward the synthesis of novel drug-like molecules with favorable bioactivity and pharmacokinetic properties.

The Ag-promoted α-C-H arylation of alcohols

We herein report the functionalization of α-C-H in alcohols through cross-dehydrogenative coupling reactions. Selectfluor was used as a mild oxidant. In situ-generated HF participated in the reaction and no external strong acid was necessary. A variety of heteroaryl-substituted alcohols were achieved with good yields and with good functional group tolerance.

Visible light-induced direct α C-H functionalization of alcohols

Considering the synthetic value of introducing active alcoholic hydroxyl group, developing C-H functionalization of alcohols is of significance. Herein, we present a photochemical method that under visible light irradiation, selectfluor can effectively promote the oxidative cross-coupling between alcohols and heteroarenes without the external photocatalysis, achieving the selective α sp³ C-H arylation of alcohol, even in the presence of ether. The N-F activation of selectfluor under blue LEDs irradiation is evidenced by electron paramagnetic resonance (EPR) study, which is the key process for the oxidative activation of α sp³ C-H alcohols. The observed reactivity may have significant implications for chemical transformations.

Photoredox-mediated remote C(sp3)-H heteroarylation of free alcohols

We report an efficient and economical method for remote δ C(sp3)-H heteroarylation of free aliphatic alcohols using a hypervalent iodine PFBI-OH oxidant under photoredox catalysis. The reaction sequence involves in situ alcoholysis of PFBI-OH with alcohol, generation of an alkoxy radical intermediate by SET reduction, 1,5-HAT, and Minisci-type C-C bond formation. This method uses a slight excess of alcohols, can facilitate reaction at δ methyl and methylene positions, and has been successfully applied to modification of complex drug molecules.

Site-specific hydroxyalkylation of chromones via alcohol mediated Minisci-type radical conjugate addition

The metal-free C2-functionalization of chromones with alcohols and ethers via radical sp³ C–H activation was developed.

C-H Functionalization of Azines

Azines, which are six-membered aromatic compounds containing one or more nitrogen atoms, serve as ubiquitous structural cores of aromatic species with important applications in biological and materials sciences. Among a variety of synthetic approaches toward azines, C-H functionalization represents the most rapid and atom-economical transformation, and it is advantageous for the late-stage functionalization of azine-containing functional molecules. Since azines have several C-H bonds with different reactivities, the development of new reactions that allow for the functionalization of azines in a regioselective fashion has comprised a central issue. This review describes recent advances in the C-H functionalization of azines categorized as follows: (1) S_NAr reactions, (2) radical reactions, (3) deprotonation/functionalization, and (4) metal-catalyzed reactions.

Selective and tunable synthesis of 3-arylsuccinimides and 3-arylmaleimides from arenediazonium tetrafluoroborates and maleimides

A highly efficient and tunable synthetic strategy for 3-arylsuccinimides or 3-arylmaleimides has been developed from arenediazonium tetrafluoroborates and maleimides with satisfactory yields in the presence of TiCl₃ or CuCl.