Visible Light-Driven α-Alkylation of N-Aryl tetrahydroisoquinolines Initiated by Electron Donor-Acceptor Complexes

Electron Donor-Acceptor Complex Driven Photocatalyst-Free Trifluoromethylation of Heterocycles

Heterocyclic trifluoromethylation is efficiently initiated through a photochemical reaction utilizing an electron donor-acceptor (EDA) complex, proceeding smoothly without the use of photocatalysts, transition-metal catalysts, or additional oxidants. This method has been optimized through extensive experimentation, demonstrating its versatility and efficacy across various substrates, including quinoxalinones, coumarins, and indolones. Notably, this approach enables the practical synthesis of trifluoromethylated quinoxalinones on a gram scale. Mechanistic investigations that incorporate radical trapping and ultraviolet/visible spectroscopy, confirmed the formation of the an EDA complex and elucidated the reaction pathways. This study highlights the crucial role of EDA photoactivation in trifluoromethylation, significantly expanding the application scope of EDA complexes in chemical synthesis.

Isonitriles as Alkyl Radical Precursors in Visible Light Mediated Hydro- and Deuterodeamination Reactions

Herein, we report the use of isonitriles as alkyl radical precursors in light-mediated hydro- and deuterodeamination reactions. The reaction is scalable, shows broad functional group compatibility and potential to be used in late-stage functionalization. Importantly, the method is general for Cα -primary, Cα -secondary and Cα -tertiary alkyl isonitriles. For most examples, high yields were obtained through direct visible-light irradiation of the isonitrile in the presence of a silyl radical precursor. Interestingly, in the presence of an organic photocatalyst (4CzIPN) a dramatic acceleration was observed. In-depth mechanistic studies using UV/Vis absorption, steady-state and time-resolved photoluminescence, and transient absorption spectroscopy suggest that the excited state of 4CzIPN can engage in a single-electron transfer with the isonitrile.

Enhanced basicity of an electron donor-acceptor complex

An electron donor-acceptor (EDA) complex forms between 1,4-dicyanobenzene and N-phenylpyrrolidine, which are coupling partners for the α-aminoarylation photoredox reaction. Calculations and experiments demonstrate the EDA complex is a better base than N-phenylpyrroline. A re-analysis of the α-aminoarylation reaction suggests that the EDA complex is a proton acceptor in the reaction.

Visible Light Driven Metal-Free Photoredox Catalyzed α-benzylation and α-oxygenation of N-substituted tetrahydroisoquinolines: Applications to Synthesis of Natural Products

Herein, visible light mediated organophoto redox catalysed simple and convenient method for the a-benzylation and a-oxygenation of tertiary amines is demonstrated. Synthesis of novel thiophenol based donor acceptor organophotoredox catalysts 4a - 4d were investigated along with commercial catalyst 4-CzIPN ( 4e ). A diverse biologically active a-benzylated tetrahydroisoquinolines and natural products such as (±)-Norlaudanosine, (±)-laudanosine and (±)-xylopinine have been synthesized under the optimized conditions in yields ranging from from 62-91%. Exploitation of synthesized a-benzylated compound using present phtoredox catalyzed conditions gave rise to dehydyrogenative benzylic oxidation product under oxygen atmosphere which is known to display biologically and structurally important properties. Also, various N-protected tertiary amines were found to be suitable for the a-oxygenation reactions using catalyst 4e and resulted in good yields (61-85%).

Solid-Phase Peptide Modification via Deaminative Photochemical Csp3 -Csp3 Bond Formation Using Katritzky Salts

Introduction of unnatural amino acids can significantly improve the binding affinity and stability of peptides. Commercial availability of such amino acids is limited, and their synthesis is a long and tedious process. We here describe a method that allows the functionalization of peptides directly on solid-support by converting lysine residues to Katritzky salts, and subjecting them to a photochemical Giese reaction under mild reaction conditions. The method avoids the need for amino acid synthesis and instead offers a late-stage modification route for rapid peptide diversification. While numerous modification approaches at the lysine amine have been described, this work provides the first example of deaminative functionalization of peptides at lysine. The two-step protocol is compatible with various substrates, lysine analogues, resins, and all proteinogenic amino acids. Finally, by leveraging solid-phase modification, this protocol facilitates the functionalization of longer peptides as was demonstrated using biologically relevant peptides of up to 15 amino acids.

Recent Progress in Fragmentation of Katritzky Salts Enabling Formation of C-C, C-B, and C-S Bonds

Since their discovery in 1970s, Katritzky salts have emerged as one of the most important classes of building blocks for use in organic synthesis and drug discovery. These bulky pyridinium salts derived from alkylamine can readily generate alkyl radical and undergo a variety of organic transformation reactions such as alkylation, arylation, alkenylation, alkynylation, carbonylation, sulfonylation, and borylation. Through these transformations, complexed molecules bearing new C-C, C-B, or C-S bonds can be constructed in easy ways and in simple steps. This review aims to summarize recent advances in these versatile building blocks in well-classified categories. Representative examples and their reaction mechanisms are discussed. The hope is to provide the scientific community with convenient access to collective information and accelerate further research.

Visible-Light-Promoted Unsymmetrical Phosphine Synthesis from Benzylamines

Herein, by applying visible-light photoredox catalysis, we have achieved the catalytic deaminative alkylation of diphenylphosphine and phenyl phosphine with benzylamine-derived Katritzky salts at room temperature. The use of Eosin Y as photoredox catalyst and visible light can largely promote the reaction. A series of unsymmetrical tertiary phosphines were successfully synthesized, including phosphines with three different substituents that are otherwise difficult to obtain.

Visible-Light-Driven Photoredox-Catalyzed C(sp3)-C(sp3) Cross-Coupling of N-arylamines with Cycloketone Oxime Esters

A novel photoredox-catalyzed C(sp3)-C(sp3) cross-coupling between N-arylamines and cycloketone oxime esters under mild conditions has been accomplished. The redox-neutral reaction proceeds good functional group tolerance and excellent regioselectivity without any...

The Photocatalyst-Free Cross-Dehydrogenative Coupling Reaction Enabled by Visible-Light Direct Excitation of Substrate

A new photocatalyst-free strategy for the cross-dehydrogenative C-C and C-P coupling reaction has been described. This protocol provides a concise method to synthesize various 1-substituted tetrahydroisoquinoline (THIQ) derivatives enabled by visible-light direct excitation of substrates without using any photocatalyst. Moreover, a wide substrate scope demonstrated good synthetic versatility and practicality.

α-Chiral Amines via Thermally Promoted Deaminative Addition of Alkylpyridinium Salts to Sulfinimines

A deaminative reaction of Katritzky alkylpyridinium salts and sulfinimines has been developed to deliver enantiopure α-chiral amines. The success of this method relied on the discovery of a thermally promoted deamination via single-electron transfer of an anion-π complex of the alkylpyridinium cation with potassium carbonate. This method boasts excellent diastereoselectivity over the α-stereocenter as well as broad functional group and heterocycle tolerance.

Deaminative Reductive Methylation of Alkylpyridinium Salts

Methyl groups can imbue valuable properties in organic molecules, often leading to enhanced bioactivity. To enable efficient installation of methyl groups on simple building blocks and in late-stage functionalization, a nickel-catalyzed reductive coupling of secondary Katritzky alkylpyridinium salts with methyl iodide was developed. When coupled with formation of the pyridinium salt from an alkyl amine, this method allows amino groups to be readily transformed to methyl groups with broad functional group and heterocycle tolerance.

Phosphite mediated asymmetric N to C migration for the synthesis of chiral heterocycles from primary amines

A phosphite mediated stereoretentive C-H alkylation of N-alkylpyridinium salts derived from chiral primary amines was achieved. The reaction proceeds through the activation of the N-alkylpyridinium salt substrate with a nucleophilic phosphite catalyst, followed by a base mediated [1,2] aza-Wittig rearrangement and subsequent catalyst dissociation for an overall N to C-2 alkyl migration. The scope and degree of stereoretention were studied, and both experimental and theoretical investigations were performed to support an unprecedented aza-Wittig rearrangement-rearomatization sequence. A catalytic enantioselective version starting with racemic starting material and chiral phosphite catalyst was also established following our understanding of the stereoretentive process. This method provides efficient access to tertiary and quaternary stereogenic centers in pyridine systems, which are prevalent in drugs, bioactive natural products, chiral ligands, and catalysts.

Photocatalyst- and additive-free decarboxylative alkylation of N-aryl tetrahydroisoquinolines induced by visible light

A photocatalyst- and additive-free visible light induced decarboxylative alkylation of N-aryl tetrahydroisoquinolines has been developed using tetrachloro-N-hydroxyphthalimide esters as alkylation agents.

Electron Donor-Acceptor Complex-Initiated Photochemical Cyanation for the Preparation of α-Amino Nitriles

An electron donor-acceptor complex-initiated α-cyanation of tertiary amines has been described. The reaction protocol provides a novel method to synthesize various α-amino nitriles under mild conditions. The reaction can proceed smoothly without the presence of photocatalysts and transition metal catalysts, and either oxidants are unnecessary or O₂ is the only oxidant. The practicality of this method is showcased not only by the late-stage functionalization of natural alkaloid derivatives and pharmaceutical intermediate, but also by the applicability of a stop-flow microtubing reactor.