Photoinduced Deaminative Borylation of Unreactive Aromatic Amines Enhanced by CO2

Desulfurative Borylation of Small Molecules, Peptides, and Proteins

We introduce a direct conversion of alkyl thiols into boronic acids, facilitated by a water-soluble phosphine, 1,3,5-triaza-7-phosphaadamantane (PTA), in conjunction with tetrahydroxydiboron (B2(OH)4), acting as both a radical initiator and a boron source. This desulfurative borylation reaction has been successfully applied to various substrates, including cysteine residues in oligopeptides and small proteins, primary alkyl thiols found in pharmaceutical compounds, disulfides, and selenocysteine. Optimization of reaction conditions was undertaken to reduce the formation of unwanted reactions, such as the reduction of alanyl or other primary radicals, and to prevent deleterious reactions between the phosphine and N-terminal amine that lead to methylene adducts by utilizing a buffer containing glycine-glycine (GG) dipeptide. The developed method is characterized by its operational simplicity and robustness. Moreover, its compatibility with various functional groups present in peptides and proteins makes it a promising tool for late-stage functionalization, extending its potential application across a broad spectrum of chemical and biological targets.

Bifunctional 1-Hydroxypyrene Photocatalyst for Hydrodesulfurization via Reductive C(Aryl)-S Bond Cleavage

We developed the visible-light-induced hydrodesulfurization of alkyl aryl thioethers via the reductive cleavage of the C(aryl)-S bond using 1-hydroxypyrene as a Brønsted acid-reductant bifunctional photocatalyst. The hydrodesulfurization reaction proceeded under simple reaction conditions (1-hydroxypyrene and Et₃N in THF under purple LED illumination); this reaction did not require chemicals commonly used for hydrodesulfurization, such as hydrosilanes, transition metal catalysts, and/or stoichiometric amounts of metal reagents. Detailed mechanistic studies based on control experiments, spectroscopic measurements, and computational studies revealed that the cleavage of the C(aryl)-S bond and the formation of the C(aryl)-H bond proceeded via the formation of the ion pair between the radical anion of alkyl aryl thioether and Et₃N⁺H, resulting in the generation of a sulfur radical. In addition, the 1-hydroxypyrene catalyst was regenerated via hydrogen atom transfer (HAT) from Et₃N.

Transition Metal-Free Aromatic C-H, C-N, C-S and C-O Borylation

Aromatic organoboron compounds are highly valuable building blocks in organic chemistry. They were mainly synthesized through aromatic C-H and C-Het borylation, in which transition metal-catalysis dominate. In the past decade, with increasing attention to sustainable chemistry, numerous transition metal-free C-H and C-Het borylation transformations have been developed and emerged as efficient methods towards the synthesis of aromatic organoboron compounds. This account mainly focuses on recent advances in transition metal-free aromatic C-H, C-N, C-S, and C-O borylation transformations and provides insights to where further developments are required.

Photoinduced Divergent Deaminative Borylation and Hydrodeamination of Primary Aromatic Amines

We have developed the divergent deaminative borylation and hydrodeamination of primary aromatic amines using bis(pinacolato)diboron. These transformations can be switched by the reaction conditions. Mechanistic and computational studies have suggested that the cleavage of the C-N bond and the formation of C-B bond are unlikely to involve free aryl radical intermediates. However, hydrodeamination is shown to proceed via hydrogen atom transfer between the corresponding aryl radical and an ethereal solvent.

Photoinduced Organic Reactions by Employing Pyrene Catalysts

Pyrene is one of the most attractive polycyclic aromatic hydrocarbons (PAHs) in photochemistry. Based on their redox properties, pyrenes have potential as photosensitizers. In this review, we summarize recent developments in pyrene-catalyzed photoinduced organic reactions occurring via energy transfer or single-electron transfer based on the excited state of the pyrene.

1 Introduction

2 Photolysis Involving N–O Bond Cleavage or Decarboxylation

3 (Cyclo)addition Reactions with Styrenes

4 Transformations via Cleavage of C–F, C–I, C–S and C–N Bonds

5 Reactions Based on Sensitization-Initiated Electron Transfer (SenI­-ET)

6 Miscellaneous Transformations

7 Conclusion

Synthesis of Flavanone and Quinazolinone Derivatives from the Ruthenium-Catalyzed Deaminative Coupling Reaction of 2'-Hydroxyaryl Ketones and 2-Aminobenzamides with Simple Amines

The cationic Ru-H complex [(C₆H₆)(PCy₃)(CO)RuH]⁺BF₄^- (1) with 3,4,5,6-tetrachloro-1,2-benzoquinone (L1) was found to be a highly effective catalyst for the deaminative coupling reaction of 2'-hydroxyaryl ketones with simple amines to form 3-substituted flavanone products. The analogous deaminative coupling reaction of 2-aminobenzamides with branched amines directly formed 3,3-disubstituted quinazolinone products. The catalytic method efficiently installs synthetically useful flavanone and quinazolinone core structures without employing any reactive reagents.

Unreactive C-N Bond Activation of Anilines via Photoinduced Aerobic Borylation

Unreactive C-N bond activation of anilines was achieved by photoinduced aerobic borylation. A diverse range of tertiary and secondary anilines were converted to aryl boronate esters in moderate to good yields with wide functional group tolerance under simple and ambient photochemical conditions. This transformation achieved the direct and facile C-N bond activation of unreactive anilines, providing a convenient and practical route transforming widely available anilines into useful aryl boronate esters.

Copper-catalyzed deaminative alkynylation of secondary amines with alkynes: selectivity switch in the synthesis of diverse propargylamines

The copper-catalyzed selective deamination and alkynylation of the unsymmetrical secondary amines with terminal alkynes was reported with a broad substrate scope and excellent functional compatibility.