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

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.

No-Deuterium Proton (No-D) NMR as a Convenient Method for Analysis of Organic Solvents

NMR spectra of 25 neat solvents have been recorded using No-D (no-deuterium proton) NMR, and water signals are visible in all spectra. Larger amounts of water can be measured by integration. Water can easily be detected at 0.01% (100 ppm), and amounts can be estimated by comparison with solvent 13C satellite peaks. Molecular sieves efficiently remove water from most solvents such that it cannot be detected by this NMR method. Additives in halogenated solvents and peroxides in ether and THF are also easily detected by No-D NMR.

Asymmetric Ketoalkylation/Rearrangement of Alkyenlfurans via Synergistic Photoredox/Brønsted Acid Catalysis

An enantioselective three-component rearrangement of alkenylfurans with various cycloalkyl silyl peroxides and anilines has been developed by merging photoredox catalysis with chiral Brønsted acid catalysis. This protocol provides expedient access to a broad spectrum of ketoalkyl-functionalized 4-aminocyclopentenones in high yields with excellent enantio- and diastereoselectivities. Diverse functional groups can be introduced via facile product derivations.

Sulfuric Acid Immobilized on Activated Carbon Aminated with Ethylenediamine: An Efficient Reusable Catalyst for the Synthesis of Acetals (Ketals)

Through the amination of oxidized activated carbon with ethylenediamine and then the adsorption of sulfuric acid, a strong carbon-based solid acid catalyst with hydrogen sulfate (denoted as AC-N-SO₄H) was prepared, of which the surface acid density was 0.85 mmol/g. The acetalization of benzaldehyde with ethylene glycol catalyzed by AC-N-SO₄H was investigated. The optimized catalyst dosage accounted for 5 wt.% of the benzaldehyde mass, and the molar ratio of glycol to benzaldehyde was 1.75. After reacting such mixture at 80 °C for 5 h, the benzaldehyde was almost quantitatively converted into acetal; the conversion yield was up to 99.4%, and no byproduct was detected. It is surprising that the catalyst could be easily recovered and reused ten times without significant deactivation, with the conversion yield remaining above 99%. The catalyst also exhibited good substrate suitability for the acetalization of aliphatic aldehydes and the ketalization of ketones with different 1,2-diols.

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.

Diastereoselective Synthesis of Aryl C-Glycosides from Glycosyl Esters via C-O Bond Homolysis

C-aryl glycosyl compounds offer better in vivo stability relative to O- and N-glycoside analogues. C-aryl glycosides are extensively investigated as drug candidates and applied to chemical biology studies. Previously, C-aryl glycosides were derived from lactones, glycals, glycosyl stannanes, and halides, via methods displaying various limitations with respect to the scope, functional-group compatibility, and practicality. Challenges remain in the synthesis of C-aryl nucleosides and 2-deoxysugars from easily accessible carbohydrate precursors. Herein, we report a cross-coupling method to prepare C-aryl and heteroaryl glycosides, including nucleosides and 2-deoxysugars, from glycosyl esters and bromoarenes. Activation of the carbohydrate substrates leverages dihydropyridine (DHP) as an activating group followed by decarboxylation to generate a glycosyl radical via C-O bond homolysis. This strategy represents a new means to activate alcohols as a cross-coupling partner. The convenient preparation of glycosyl esters and their stability exemplifies the potential of this method in medicinal chemistry.

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.

Iron catalyzed ketoalkylation and ketoalkylation/etherification of styrenes initiated by selective C–C bond cleavage

A mild and efficient iron-catalyzed ketoalkyl-Heck-type coupling initiated by radical C–C bond cleavage is described. Furthermore, this concise catalytic system was also applicable for the three-component ketoalkylation/etherification of styrenes.