Copper-catalyzed N-methylation/ethylation of sulfoximines

Magic methylation with methyl-containing peroxides

Methyl groups rank among the most abundant carbon fragments found in natural products and small-molecule pharmaceuticals. The late-stage and environmentally friendly installation of these groups onto biologically active molecules has attracted widespread attention in both industry and academia. In 2008, we published the first use of a methyl radical derived from a peroxide toward a directed transition-metal catalysed C-H methylation. In the past sixteen years, methyl-containing peroxides have proven themselves as robust reagents for introducing methyl groups onto organic molecules. In this review, our goal is to provide a thorough summary of the research advancements achieved in this field thus far.

Introduction of Lipophilic Side Chains to NH-Sulfoximines by Palladium Catalysis Under Blue Light Irradiation

Palladium catalysis under blue (LED) light irradiation allows conversion of NH-sulfoximines into products with long lipophilic side chains attached to the S═N moiety. The three-component reactions involve both radicals and organometallic intermediates stemming from alkyl bromides and butadienes. The substrate scope is broad, and the products are formed in moderate to good yields.

Di-tert-butyl peroxide as an effective two-carbon unit in oxidative radical cyclization toward 7-methylazolo[1,5-a]pyrimidines

An unexpected oxidative radical cyclization with DTBP as the C2 cyclic unit enables the assembly of privileged 7-methylazolo[1,5-a]pyrimidines.

The construction of benzimidazo[2,1-a]isoquinolin-6(5H)-ones from N-methacryloyl-2-phenylbenzoimidazoles through radical strategies

Benzimidazo[2,1-a]isoquinolin-6(5H)-one constitutes a structurally unique class of tetracyclic N-heterocycles that are found throughout a myriad of biologically active natural products, pharmaceutical compounds, and functional materials. Various synthetic routes for the preparation of benzimidazo[2,1-a]isoquinolin-6(5H)-ones have been reported. In particular, the use of N-methacryloyl-2-phenylbenzoimidazoles to construct benzimidazo[2,1-a]isoquinolin-6(5H)-ones through various radical strategies have attracted widespread attention due to the versatility and simple preparation of raw materials, as well as the step-economy and mild reaction conditions. Using representative examples, we highlight significant progress in the synthesis of benzimidazo[2,1-a]isoquinolin-6(5H)-ones, including the selection of the catalytic system, substrate scope, mechanistic understanding, and applications. The contents of this review focus on the development of C-, S-, P-, and Si-centered radical addition-intramolecular cyclization strategies.

Synthesis and Configurational Assignment of Vinyl Sulfoximines and Sulfonimidamides

Vinyl sulfones and sulfonamides are valued for their use as electrophilic warheads in covalent protein inhibitors. Conversely, the S(VI) aza-isosteres thereof, vinyl sulfoximines and sulfonimidamides, are far less studied and have yet to be applied to the field of protein bioconjugation. Herein, we report a range of different synthetic methodologies for constructing vinyl sulfoximine and vinyl sulfonimidamide architectures that allows access to new areas of electrophilic chemical space. We demonstrate how late-stage functionalization can be applied to these motifs to incorporate alkyne tags, generating fully functionalized probes for future chemical biology applications. Finally, we establish a workflow for determining the absolute configuration of enantioenriched vinyl sulfoximines and sulfonimidamides by comparing experimentally and computationally determined electronic circular dichroism spectra, enabling access to configurationally assigned enantiomeric pairs by separation.

Peroxide-mediated synthesis of benzimidazo[2,1-a]isoquinoline-6(5H)-ones via cascade methylation/ethylation and intramolecular cyclization

A metal-free oxidative radical methylation/arylation of 2-arylbenzoimidazoles with DTBP as the oxidant and methyl radical source was developed. The reaction proceeds through a sequential methyl radical addition/cyclization pathway and affords a series of methyl functionalized benzimidazo[2,1-a]isoquinoline-6(5H)-ones in moderate to good yields. Besides, the ethylation/arylation of 2-arylbenzoimidazoles was also achieved with DTAP.

General Method for the Asymmetric Synthesis of N-H Sulfoximines via C-S Bond Formation

A versatile method for the synthesis of enantioenriched N-H sulfoximines is reported. The approach stems from the organomagnesium-mediated ring opening of novel cyclic sulfonimidate templates. The reactions proceed in high yield and with excellent stereofidelity with alkyl, aryl, and heteroaryl Grignard reagents. The chiral auxiliary is readily removed from the resultant sulfoximines via an unusual oxidative debenzylation protocol that utilizes molecular oxygen as the terminal oxidant. This provides a general strategy for the synthesis of highly enantioenriched N-H sulfoximines.

N-(2,3,5,6-Tetrafluoropyridyl)sulfoximines: synthesis, X-ray crystallography, and halogen bonding

N-(Tetrafluoropyridyl)sulfoximines are obtained from NH-sulfoximines and pentafluoropyridine under solution-based or mechanochemical conditions, and the solid-state structures of 26 products have been determined by X-ray diffraction analysis.

Copper-catalyzed methylative difunctionalization of alkenes

Trifluoromethylative difunctionalization and hydrofunctionalization of unactivated alkenes have been developed into powerful synthetic methodologies. On the other hand, methylative difunctionalization of olefins remains an unexplored research field. We report in this paper the Cu-catalyzed alkoxy methylation, azido methylation of alkenes using dicumyl peroxide (DCP), and di-tert-butyl peroxide (DTBP) as methyl sources. Using functionalized alkenes bearing a tethered nucleophile (alcohol, carboxylic acid, and sulfonamide), methylative cycloetherification, lactonization, and cycloamination processes are subsequently developed for the construction of important heterocycles such as 2,2-disubstituted tetrahydrofurans, tetrahydropyrans, γ-lactones, and pyrrolidines with concurrent generation of a quaternary carbon center. The results of control experiments suggest that the 1,2-alkoxy methylation of alkenes goes through a radical-cation crossover mechanism, whereas the 1,2-azido methylation proceeds via a radical addition and Cu-mediated azide transfer process.

While the trifluoromethylative difunctionalization of unactivated alkenes has been largely explored, methylative difunctionalization remains underinvestigated. Here, the authors report copper-catalyzed alkoxy- and azido-methylation reactions of alkenes leading to important synthetic building blocks and valuable O- and N-heterocycles.

Synthesis ofN-sulfenyl-sulfoximines and -sulfenamides through a metal-free N–H/S–H dehydrocoupling reaction

A metal-free, iodine-catalyzed N–H/S–H dehydrocoupling reaction of sulfoximines and anilines with various thiols to construct sulfur–nitrogen bonds has been developed.

Copper promoted N-alkylation of sulfoximines with alkylboronic acid under mild conditions

The copper meditated N-methylation of sulfoximines using methylboronic acid is reported. The reactions provide excellent yields in a short span of time under mild conditions. The optimized conditions were also found to be suitable for the N-alkylation of sulfoximine with different alkylboronic acids. In addition, N-methylation and cyclopropylation of the bioactive l-methionine sulfoximine derivative was demonstrated under standard reaction conditions.

Mechanistic investigation of the NH-sulfoximination of sulfide. Evidence for λ6-sulfanenitrile intermediates

One-pot synthesis of NH-sulfoximines from sulfides was reported through fully described acetoxy- and methoxy-λ⁶-sulfanenitrile intermediates (¹H, ¹³C, ¹⁵N NMR and HRMS).

Bis(trialkylsilyl) peroxides as alkylating agents in the copper-catalyzed selective mono-N-alkylation of primary amides

The copper-catalyzed selective mono-N-alkylation of primary amides with bis(trialkylsilyl) peroxides as alkylating agents was reported.

Metal-Free Oxidative 1,2-Arylmethylation Cascades of N-(Arylsulfonyl)acrylamides Using Peroxides as the Methyl Resource

A new, metal-free oxidative 1,2-arylmethylation cascades of N-(arylsulfonyl)acrylamides for the assembly of 2,2-disubstituted-N-arylbutanamides containing an all-carbon quaternary center is presented. This reaction enables the one-step formation of two new C-C bonds through a sequence of methylation/1,4-aryl migration/desulfonylation using an organic peroxide as the methyl resource with a broad substrate scope and excellent functional group tolerance.

Stereoselective synthesis of 4-aminobenzo[c][1,2]thiazine via modification of the Harmata benzothiazine synthesis

A stereoselective synthesis of 4-aminobenzothiazines was developed through a modified Harmata benzothiazine synthesis.

Copper-catalyzed N-thioetherification of sulfoximines using disulfides

A novel copper-catalyzed N-thioetherification of sulfoximines under mild reaction conditions was developed using readily available disulfides as the sulfur source.

The N-silylation of sulfoximines

The copper-catalyzed N-silylation of sulfoximines was achieved in good to moderate yields in the presence of di-tert-butyl peroxide.