Photoredox Nucleophilic (Radio)fluorination of Alkoxyamines

Dual Activation of Organoboron for the Ion-Pair-Mediated Synthesis of Hindered Alkyl Fluorides

A novel electrochemical approach for the synthesis of hindered alkyl fluorides has been developed. The protocol grants access to a diverse array of tertiary and secondary alkyl fluorides using readily attainable organoboron precursors under mild conditions. The efficiency of the system stems from the dual activation of the redox-active borate intermediate, providing both electrophilic and nucleophilic reaction partners in the form of an internally generated ion pair.

Formation of TEMPO Adducts with Hydrogen Atom Transfer: An Alternative Pathway to Versatile Hydrofunctionalizations of Olefins

A two-step process is developed to access a broad range of hydrofunctionalization of olefins, by combining a cobalt-catalyzed formation of TEMPO adduct from olefins and a photocatalytic nucleophilic addition to generate a new C-C, C-N, C-O, C-F, and C-Cl bond. Nucleophilic fluorination can be achieved with a short reaction time, showing its potential in PET applications. Combining the two steps, net hydrofunctionalization of olefins with a broad range has been achieved.

Through Space π-Electrons Communication in [2,2]-Paracyclophanes: Unprecendented Stabilization of Radicals

Efforts to understand radical stability have led to considerable progress in radical chemistry. In this article, we investigated a novel approach to enhancing the radical stability of carbon-centered radicals through space electron delocalization within [2,2]-paracyclophanes. Alkoxyamines possessing a paracyclophane scaffold exploit face-to-face π-π-interactions between the aromatic rings to effectively lower bond dissociation energy (BDE) for NO-C bond homolysis. Electron spin resonance (ESR) experiments and computational modeling have confirmed a better stability compared to the analogues without the paracyclophane core. Theoretical analyses further elucidate the role of through-space electron communication in enhancing radical stability. This study highlights promising applications in fields such as organic synthesis, material science, and drug design. By achieving a low BDE for homolysis, the alkoxyamines efficiently release radicals, enabling successful application in nitroxide-mediated polymerization (NMP) of styrene, which provides high control over polymer architecture. Additionally, preliminary anti-proliferative assays reveal that the alkoxyamines exhibit promising anti-cancer activities against lung, breast, and prostate cells, which is correlated to their ability to release radicals upon homolysis.

Cryogenic Organometallic Carbon-Fluoride Bond Functionalization with Broad Functional Group Tolerance

The unique properties of fluorinated organic compounds have received intense interest and have conquered a myriad of applications in the chemical and pharmaceutical sciences. Today, an impressive range of alkyl fluorides are commercially available, and there are many practical methods to make them exist. However, the unmatched stability and inertness of the C-F bond have largely limited its synthetic value, which is very different from the widely accepted utility of alkyl chlorides, bromides, and iodides that serve everyday as "workhorse" building blocks in countless carbon-carbon bond forming reactions. This study demonstrates practical and high-yielding functionalization of the C-F bond under mild conditions, i.e., at temperatures as low as -78 °C, in short reaction times and with unconventional chemoselectivity. Cryogenic Csp3-F bond cleavage using fluorophilic organoaluminum compounds together with fast nucleophile transfer of intermediate ate complexes forge carbon-carbon bonds with unactivated primary, secondary, and tertiary alkyl fluorides alike. This method, which exploits the stability of the Al-F bond as the thermodynamic driving force, is highly selective toward Csp3-F bond functionalization, whereas many other functional groups including alkyl chloride, bromide, iodide, aryl halide, alkenyl, alkynyl, difluoroalkyl, trifluoromethyl, ether, ester, hydroxyl, acetal, heteroaryl, nitrile, nitro, and amide groups are tolerated, which is an unexpected reversal of long-standing main group organometallic and alkyl halide cross-coupling reactivity and compatibility patterns. As a result, the strongest single bond in organic chemistry can now be selectively targeted in high-yielding arylation, alkylation, alkenylation, and alkynylation reactions and used in late-stage functionalization applications that are complementary to currently available methods.

Preparation of Difluoromethylated Benzothiophene by Visible-Light-Mediated Alkyne Difunctionalization Reaction

An efficient method for the preparation of difluoromethylated benzothiophenes via visible-light-mediated alkyne difunctionalization was developed. In this method, inexpensive sodium difluoromethanesulfinate (HCF2SO2Na) was used as the fluorine source, and a variety of benzothiophene derivatives were obtained in moderate to excellent yield under mild reaction conditions. Moreover, the reaction operation is simple and easy to scale up.