Synthesis of Functionalized Organoboron/Silicon Compounds by Copper-Catalyzed Coupling of Alkylsilyl Peroxides and Diboron/Silylborane Reagents

Synthesis of Functionalized Organosilicon Compounds/Distal Ketones via Ring-Opening Giese Addition of Cycloalkanols under Organophotocatalytic Conditions

Visible-light-induced organophotocatalyzed ring-opening followed by remote Giese addition of tertiary cycloalkanols with β-silylmethylene malonates has been developed under mild reaction conditions for the synthesis of organosilicon compounds, bearing a ketone group distally substituted with a silyl group with an additional dialkyl malonate functional handle in moderate to good yields (34-72%). The protocol also worked well with diverse Michael acceptors, such as alkylidene/benzylidene malonates, trifluoro methylidene malonate, benzylidene malononitrile, α-cyano-enone, and α-cyano vinyl sulfone, and delivered desired valuable distally functionalized ketones. To showcase the potential of the method, various synthetic transformations of the obtained product were also demonstrated.

Copper-catalyzed oxidative cyclization of 2-(1H-pyrrol-1-yl)aniline and alkylsilyl peroxides: a route to pyrrolo[1,2-a]quinoxalines

An efficient method was developed for the one-pot construction of pyrrolo[1,2-a]quinoxalines via a Cu(II)-catalyzed domino reaction between 2-(1H-pyrrol-1-yl)anilines and alkylsilyl peroxides. This reaction proceeds through C-C bond cleavage and new C-C and C-N bond formation. A mechanistic study suggests that alkyl radical species participate in the cascade reaction.

NHC-catalyzed radical acylation of cycloalkyl silyl peroxides to access 1,6-,1,7-, and 1,8-diketones

An unprecedented N-heterocyclic carbene (NHC)-catalyzed radical acylation of cycloalkyl silyl peroxides was developed using readily available aldehydes as the acylating agents. This protocol provides an exceptionally useful method for the efficient and rapid synthesis of long-chain 1,6-/1,7-/1,8-diketones, especially unsymmetrical ones. This strategy also has the advantages of mild conditions, good functional group compatibility, and potential applications in the late-stage functionalization of aldehydes with bioactive fragments and in the construction of long-chain complex bioactive molecules.

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.

Fe-Catalyzed Three-Component Coupling Reaction of α,β,γ,δ-Unsaturated Carbonyl Compounds and Conjugate Dienes with Alkylsilyl Peroxides and Nucleophiles

An Fe(OTf)₂-catalyzed three-component coupling reaction of α,β,γ,δ-unsaturated carbonyl compounds with alkylsilyl peroxides in the presence of certain heteronucleophiles (ROH and indole) is realized under mild reaction conditions. A variety of α,β,γ,δ-diene carbonyl substrates with different substituents were successfully employable via combination with several different alkylsilyl peroxides. This new approach is also applicable to the double functionalization of diene substrates.

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.

First-Row d-Block Element-Catalyzed Carbon-Boron Bond Formation and Related Processes

Organoboron reagents represent a unique class of compounds because of their utility in modern synthetic organic chemistry, often affording unprecedented reactivity. The transformation of the carbon-boron bond into a carbon-X (X = C, N, and O) bond in a stereocontrolled fashion has become invaluable in medicinal chemistry, agrochemistry, and natural products chemistry as well as materials science. Over the past decade, first-row d-block transition metals have become increasingly widely used as catalysts for the formation of a carbon-boron bond, a transformation traditionally catalyzed by expensive precious metals. This recent focus on alternative transition metals has enabled growth in fundamental methods in organoboron chemistry. This review surveys the current state-of-the-art in the use of first-row d-block element-based catalysts for the formation of carbon-boron bonds.

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.

Silylative aromatization of p-quinone methides under metal and solvent free conditions

A base-mediated silylation reaction leading to benzyl silanes has been developed. Under transition-metal and solvent free conditions, the silylation of a wide array of p-quinone methides is achieved using a Cs₂CO₃ catalyst in yields up to 96%. Carboxylation of the as-obtained organosilane with gaseous CO₂ provides a new synthetic protocol for the preparation of carboxylic acid.

A novel and efficient synthetic protocol is reported for the synthesis of benzyl silanes from readily available silylborane and p-quinone methides using 5% cesium carbonate under solvent-free conditions.

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.

Activation of the Si–B interelement bond related to catalysis

Covering the past seven years, this review comprehensively summarises the latest progress in the preparation and application of Si–B reagents, including the discussion of relevant reaction mechanisms.

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.

Copper-catalyzed alkylarylation of vinylarenes with cycloalkylsilyl peroxides and boronic acids

A mild and efficient copper-catalyzed alkylarylation of vinylarenes with cycloalkylsilyl peroxides and boronic acids is described.

β-Borylation of conjugated carbonyl compounds with silylborane or bis(pinacolato)diboron catalyzed by Au nanoparticles

β-Borylation occurs in the Au/TiO₂-catalysed reaction between the silylborane Me₂PhSiBpin and conjugated carbonyl compounds, in contrast to the so far known analogous reaction catalysed by other metals, where β-silylation occurs instead.

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.