Generation of alkyl radicals from alkylsilyl peroxides and their applications to C-N or C-O bond formations

A Guide for Mono-Selective N-Methylation, N-Ethylation, and N-n-Propylation of Primary Amines, Amides, and Sulfonamides and Their Applicability in Late-Stage Modification

This review provides a comprehensive overview of mono-alkylation methodologies targeting crucial nitrogen moieties - amines, amides, and sulfonamides - found in organic building blocks and pharmaceuticals. Emphasizing the intersection of chemical precision with drug discovery, the central challenge addressed is achieving one-pot mono-selective short-chain N-alkylations (methylations, ethylations, and n-propylations), preventing undesired overalkylation. Additionally, sustainable, safe, and benign alternatives to traditional alkylating agents, including alcohols, carbon dioxide, carboxylic acids, nitriles, alkyl phosphates, quaternary ammonium salts, and alkyl carbonates, are explored. This review, categorized by the nature of the alkylating agent, aids researchers in selecting suitable methods for mono-selective N-alkylation.

Aminodealkenylation: Ozonolysis and copper catalysis convert C(sp3)-C(sp2) bonds to C(sp3)-N bonds

Great efforts have been directed toward alkene π bond amination. In contrast, analogous functionalization of the adjacent C(sp3)-C(sp2) σ bonds is much rarer. Here we report how ozonolysis and copper catalysis under mild reaction conditions enable alkene C(sp3)-C(sp2) σ bond-rupturing cross-coupling reactions for the construction of new C(sp3)-N bonds. We have used this unconventional transformation for late-stage modification of hormones, pharmaceutical reagents, peptides, and nucleosides. Furthermore, we have coupled abundantly available terpenes and terpenoids with nitrogen nucleophiles to access artificial terpenoid alkaloids and complex chiral amines. In addition, we applied a commodity chemical, α-methylstyrene, as a methylation reagent to prepare methylated nucleosides directly from canonical nucleosides in one synthetic step. Our mechanistic investigation implicates an unusual copper ion pair cooperative process.

When all C-C breaks LO-Ose

Organic peroxides are becoming popular intermediates for novel chemical transformations. The weak O-O bond is readily reduced by transition metals, including iron and copper, to initiate a radical cascade process that breaks C-C bonds. Great potential exists for the rapid generation of complexity, originating from the ability to couple the resulting free radicals with a wide range of partners. First, this review article discusses the history and synthesis of organic peroxides, providing the context necessary to understand this methodology. Then, it highlights 91 examples of recent applications of the radical functionalization of C-C bonds accessed through the transition metal-mediated reduction of organic peroxides. Finally, we provide some comments about safety when working with organic peroxides.

Visible-Light-Promoted Fe(III)-Catalyzed N-H Alkylation of Amides and N-Heterocycles

The combination of the radical chemistry of ligand-to-metal charge transfer with metal catalysis by a single iron salt helps to realize the visible-light-promoted N-H alkylation of amides and N-heterocycles. A wide variety of amides and nitrogen-containing heterocycles were tolerated in our protocol to give N-alkylated products. The applicability of this protocol was further demonstrated by late-stage alkylation of N-H-containing pharmaceuticals. Moreover, N-H-alkylated α-amino tetrahydrofurans could be transformed into versatile ring-opened amino alcohols under reducing conditions. A mechanistic study revealed that hydrogen atom transfer by a tert-butoxyl radical and a chlorine radical was responsible for the activation of C(sp³)-H precursors.

Nickel-Catalyzed Allylic Defluorinative Cross-Electrophile Coupling with Cycloalkyl Silyl Peroxides as the Alkyl Source

Herein we demonstrate the first successful application of cycloalkyl silyl peroxides (CSP) as an electrophilic coupling partner in the cross-electrophile coupling reaction. Diverse CSP are efficiently cross-coupled with an array of α-trifluoromethyl alkenes under the catalysis of nickel with the assistance of zinc as the reducing agent. This method allows the use of unstrained CSP as the carbonyl-containing alkyl source in the allylic defluorinative reaction, to access a variety of gem-difluoroalkenes bearing a pendent ketone moiety with high functionality tolerance.

Synthesis of Functionalized Aliphatic Acid Esters via the Generation of Alkyl Radicals from Silylperoxyacetals

We describe a catalytic method for the synthesis of a variety of functionalized aliphatic acid esters using silylperoxyacetals, which are versatile alkyl radical precursors with a terminal ester moiety. In the presence of an appropriate transition-metal catalyst, the in situ generation of alkyl radicals and the subsequent bond-forming process proceeds smoothly to afford synthetically valuable aliphatic acid derivatives. The present method can be applied to the efficient synthesis of a pharmaceutically important 1,1-diarylalkane motif. In addition, a novel strategy for the synthesis of structurally diverse hydroxy acid derivatives via a C-O bond formation process that utilizes TEMPO has been developed.

The copper-catalyzed selective monoalkylation of active methylene compounds with alkylsilyl peroxides

A novel method for a mild copper-catalyzed selective monoalkylation of active methylene compounds with various alkylsilyl peroxides has been developed. The reaction has a broad substrate scope and our mechanistic studies suggest the participation of radical species in this alkylation reaction.

The Formation of C-C or C-N Bonds via the Copper-Catalyzed Coupling of Alkylsilyl Peroxides and Organosilicon Compounds: A Route to Perfluoroalkylation

The copper-catalyzed selective cleavage of alkylsilyl peroxides and the subsequent formation of carbon-carbon or carbon-nitrogen bonds with organosilicon compounds are described. The reaction proceeds under mild conditions and exhibits a broad substrate scope with respect to both cyclic and acyclic alkylsilyl peroxides in combination with carbon and nitrogen sources. In particular, this approach enables the facile radical perfluoroalkylation using commercially available perfluoroalkyltrimethylsilanes. Our mechanistic studies suggest that the reaction should proceed via a free-radical process.

Cu-Catalyzed O-alkylation of phenol derivatives with alkylsilyl peroxides

A Cu-catalyzed O-alkylation of phenol derivatives using alkylsilyl peroxides as alkyl radical precursors is described.

Ni-Catalyzed C(sp2)-H alkylation of N-quinolylbenzamides using alkylsilyl peroxides as structurally diverse alkyl sources

A Ni-catalyzed direct C-H alkylation of N-quinolylbenzamides using alkylsilyl peroxides as alkyl-radical precursors is described. The reaction forms a new C(sp3)-C(sp2) bond via the selective cleavage of both C(sp3)-C(sp3) and C(sp2)-H bonds. This transformation shows a high functional-group tolerance and, due to the structural diversity of alkylsilyl peroxides, a wide range of alkyl chains including functional groups and complex structures can be introduced at the ortho-position of readily available N-quinolylbenzamide derivatives. Mechanistic studies suggest that the reaction involves a radical mechanism.

Cu-Catalyzed Enantioselective Alkylarylation of Vinylarenes Enabled by Chiral Binaphthyl-BOX Hybrid Ligands

Transition-metal-catalyzed radical relay coupling reactions have recently emerged as one of the most powerful methods to achieve difunctionalization of olefins. However, there has been limited success in applying this method to asymmetric catalysis using an effective chiral ligand. Herein we report the Cu-catalyzed enantioselective alkylarylation of vinylarenes using alkylsilyl peroxides as alkyl radical sources. This reaction proceeds under practical reaction conditions and affords chiral 1,1-diarylalkane structures that are found in a variety of bioactive molecules. Notably, a highly enantioselective reaction was accomplished by combining chiral bis(oxazoline) ligands with chiral binaphthyl scaffolds.

Iron-Catalyzed Radical Cleavage/C-C Bond Formation of Acetal-Derived Alkylsilyl Peroxides

A novel radical-based approach for the iron-catalyzed selective cleavage of acetal-derived alkylsilyl peroxides, followed by the formation of a carbon-carbon bond is reported. The reaction proceeds under mild reaction conditions and exhibits a broad substrate scope with respect to the acetal moiety and the carbon electrophile. Mechanistic studies suggest that the present reaction proceeds through a free-radical process involving carbon radicals generated by the homolytic cleavage of a carbon-carbon bond within the acetal moiety. A synthetic application of this method to sugar-derived alkylsilyl peroxides is also described.

Cu-Catalyzed Generation of Alkyl Radicals from Alkylsilyl Peroxides and Subsequent C(sp3)-C(sp2) Cross-Coupling with Arylboronic Acids

This work describes a novel and practical method for the Cu-catalyzed C(sp³)-C(sp²) cross-coupling of alkylsilyl peroxides with arylboronic acids. The reductive cleavage of the O-O bond of alkylsilyl peroxides and the desired cross-coupling reactions to afford alkyl-substituted aromatic rings proceed smoothly at room temperature promoted by simple Cu-based catalysts and do not require activation by visible light. The results of mechanistic investigations support a radical-mediated C(sp³)-C(sp²) bond formation via β-scission of the alkoxy radicals generated from the alkylsilyl peroxides.

Hybrid Reaction Systems for the Synthesis of Alkylated Compounds Based upon Cu-Catalyzed Coupling of Radicals and Organometallic Species

A transition metal catalyzed alkylation with an alkyl halide is one of the most difficult reactions to achieve, because of the difficult oxidative addition of an alkyl-halogen bond to a metal, and the tendency of the resulting alkylmetal intermediate to undergo a β-hydride elimination reaction to give an olefin. In this review, we discuss hybrid reaction systems involving Cu catalyzed combination of radicals and organometallic species, which enable facile alkylation reactions to construct C-C and C-heteroatom bonds. This paper highlights recent progress in arylation, alkenylation, alkynylation, cyclization, addition and introduction of heteroatoms via these hybrid reaction systems.

Copper-catalyzed borylation of cycloalkylsilyl peroxides via radical C–C bond cleavage

A mild copper-catalyzed radical C–C bond cleavage/borylation of cycloalkylsilyl peroxides is described. A range of four to eight, and even twelve-membered substrates were compatible, offering rapid access to keto-functionalized alkyl boronic esters.