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An efficient and general method for the C–H alkylation of heteroarenes using unprotected amino acids as stable alkyl radical precursors is reported. This one-pot procedure is performed open to air under aqueous conditions and is effective for several natural and unnatural amino acids. Heterocycles of varying structure are suitably functionalized, and reactivity trends reflect the nucleophilic character of the radical species generated.

A cobalt-catalyzed regioselective C-3 alkylation of coumarins was realized under mild reaction conditions, during which a variety of substituted coumarins including those containing sensitive functional groups could smoothly undergo the selective C(sp2)−C(sp3) bond formation with a series of cyclic or straight-chain alkyl ethers.

The synthesis of optically active α,α-disubstituted amino acid derivatives is achieved through asymmetric amination of β-keto esters with azidodicarboxylates using a chiral lithium binaphtholate derived from BBI as catalyst.

The novel reaction conditions allow the direct mono-N-alkylation of primary aromatic amines.

α-Amino nitrile 2a was conveniently prepared in two individual steps from chiral hexafluorophosphate salt isoquinolinium (−)-8b including anodic cyanation as an efficient means to activate the sp3 C1–H bond of the THIQ nucleus. The lithiation of 2a was carried out in THF at −80 °C in the presence of LDA to produce a stable α-amino carbanion which was condensed on a large variety of alkyl halides. The resulting quaternary α-amino nitriles were subjected to a stereoselective reductive decyanation in ethanol in the presence of NaBH4 as the hydride donor to yield N-Boc-1-alkyl-THIQs (+)-10a–g in up to 97:3 er’s after removal of the chiral auxiliary group. Examination of the ORTEP view of THIQ (+)-1f revealed that the newly created stereogenic center had an absolute S configuration. Likewise, (−)-xylopinine was synthesized in four workup steps in an overall 63% yield from α-amino nitrile (+)-2b. In this process, crystallization of an enantioenriched mixture (90:10) of (−)-norlaudanosine with 1 equiv of (−)-N-a...

The enantioselective synthesis of α-acyloxy-α-alkylmalonates was developed as an efficient method for producing chiral α-tertiary alcohols, which are potentially valuable intermediates in the synthesis of natural products and pharmaceuticals. The efficient enantioselective α-alkylation of diphenylmethyl tert-butyl α-acyloxymalonates was accomplished via phase-transfer catalysis in the presence of (S,S)-3,4,5-trifluorophenyl-NAS bromide to afford the corresponding α-acyloxy-α-alkylmalonates at high chemical (up to 99%) and optical (up to 93% ee) yields, which could be readily converted to versatile chiral intermediates with a chiral α-tertiary alcohol group.

Catechol mono-ethers are an important class of phenols. They are found in a number of pharmaceuticals, flavoring agents, perfumes, and are used for the preparation of numerous drugs. Herein, we report a mild meta-selective C–H alkylation of these phenols, which is enabled by a cascade of oxidative dearomatization – radical addition – rearomatization process. The method is compatible with reactive functional groups on the parent arenol, such as olefins and halides. Primary, secondary, and teriary alkyl groups can be used, the source of which is most commonly an alkylborane. This process is operationally simple, does not require heating and generally proceeds in good yields.

The catalyst used in the environmentally benign reaction procedure is recycled and reused with decreasing activity over five catalytic cycles.

In this study; novel aryl, heteroaryl, pyrrolyl and phosphoryl groups containing pyrrolizines were synthesized by the ring annulation reaction of aryl or heteroaryl substituted α-phosphoryl-α,β-unsaturated ketones with pyrrole under mild reaction conditions. This domino reaction involves scandium triflate catalyzed addition of pyrrole to the double bond of α-phosphoryl-α,β-unsaturated ketones, carbonyl group and finally ring annulation sequences. The presented work provided a convenient way for the synthesis of novel bispyrrolic compounds.

A novel catalyst-free halogenative cyclization of N-aryl diazoamides with N-halosuccinimides (NXS) is reported for the synthesis of 3-halooxindoles through a carbene-free mechanism. N-Aryl diazoamides reacted with NXS under mild and catalyst-free conditions to afford the corresponding 3-halooxindoles in good yields. This transformation is proposed to proceed through diazonium ion formation followed by intramolecular Friedel–Crafts alkylation.

Using only catalytic amounts of alkyl halides in the reactions of poor nucleophilic amines/amides and alcohols led to a selective Hofmann N-alkylation reaction catalytic in alkyl halides, providing a practical and efficient method for the practical synthesis of mono- or di-alkylated amines/amides in high selectivities. This new method avoids the use of large amounts of bases, alkyl halides, and solvents, and generates water as the only byproduct. Preliminary mechanistic studies showed that alkyl halides are key intermediates/catalysts regeneratable in the reaction cycle.

A strategy for synthesis of γ-alkylated enones through oxidative coupling of siloxydienes and 1,3-dicarbonyl compounds is reported. This method is an interrupted form of our formal [3 + 2] cycloaddition method reported previously. The present work excels in generating all-carbon quaternary centers via C–C bond formation at the remote γ-site which is traditionally challenging to functionalize. Stereoselectivity and functional group tolerance are examined in complex systems. Double alkylation reactions are also described.

Reported herein is an unprecedented base-promoted deborylative alkylation of pyridine N-oxides using 1,1-diborylalkanes as alkyl sources. The reaction proceeds efficiently for a wide range of pyridine N-oxides and 1,1-diborylalkanes with excellent regioselectivity. The utility of the developed method is demonstrated by the sequential C-H arylation and methylation of pyridine N-oxides. The reaction also can be applied for the direct introduction of a methyl group to 9-O-methylquinine N-oxide, thus it can serve as a powerful method for late-stage functionalization.

A metal-free alkyl radical induced addition/cyclization reaction of acrylamide has been developed. The process involved C(sp3)–H bond cleavage, alkylation of the double bond, and intramolecular cyclization, which provides a new method for the synthesis of 4-substituted isoquinoline-1,3(2H,4H)-dione derivatives. In addition, the product can be easily transformed into tetrahydrofuro[2,3-c]isoquinolin-5(2H)-one derivatives in moderate yield.

A novel iridium/acid co-catalysed transfer hydrogenative coupling strategy, enabling direct alkylation of C(sp3)–H bonds and atom-economic access to alkyl chain-lengthened N-heteroaromatics from six-membered 2-alkyl cyclic amines and aldehydes, has been demonstrated. This work has built an important basis to convert cyclic amines, a class of bulk chemical raw materials, into functionalized products.

A metal-free TBHP-mediated radical alkylation of enol acetates with alcohols is described. This method provides a new route to a variety of β-hydroxy-ketones in moderate to good yields.

Rh(III)-catalyzed intermolecular chelation-assisted insertion of carbenes derived from α-diazocarbonyl compounds into non-acidic primary sp3 C–H bonds, for the first time, is reported under mild reaction conditions, thus affording a good complement to previous metal-carbenoid-induced primary C(sp3)–H insertion reactions. We believe that this method will open up a new avenue for primary sp3 C–H functionalization with α-diazocarbonyl compounds.

The diastereoselective one-pot synthesis of hexahydrocyclopenta[b]pyrrole derivatives (bicycloprolines) has been achieved by base-mediated reactions of (E)-tert-butyl 6-bromo-2-hexenoate with α-imino esters. The catalytic asymmetric version of this process has been efficiently achieved using the CuI/(R)-DTBM-Segphos complex as a catalyst following a two-step 1,3-dipolar cycloaddition/intramolecular alkylation sequence.

An efficient one-pot synthesis of a series of diversely functionalized trisubstituted 4(5)het(aroyl)-2,5(4)-het(aryl)/alkylimidazoles from readily available 1,3-bishet(aryl)monothio-1,3-diketones has been reported. This novel sequential one-pot, three step protocol, wherein three new carbon nitrogen bonds are formed in contiguous fashion, involves in situ generation of enaminones by reaction of monothio-1,3-diketones with α-substituted methylamines, followed by their α-nitrosation with sodium nitrite and subsequent base mediated intramolecular heterocyclization of the resulting α-hydroxyiminoimines to trisubstituted imidazoles in high yields under mild conditions. These newly prepared 4(5)-het(aroyl)-5(4)-het(aryl)/alkylimidazoles are shown to exist as tautomeric mixture, however, their subsequent alkylation with methyl iodide in the presence of potassium carbonate affords 1-N-methy-2,5-bishet(aryl)-4-het(aroyl)imidazoles in highly regioselective fashion in most of the cases. Synthesis of few 4(5)-(2-hydr...

The alkylation of arenes is an essential synthetic step of interest not only from the academic point of view but also in the bulk chemical industry. Despite its limitations, the Friedel-Crafts reaction is still the method of choice for most of the arene alkylation processes. Thus, the development of new strategies to synthesize alkyl arenes is a highly desirable goal, and herein, we present an alternative method to those conventional reactions. Particularly, a simple protocol for the direct C-H alkylation of unbiased arenes with alkylboronic acids in the presence of Mn(OAc)3 ⋅2H2 O is reported. Primary or secondary unactivated alkylboronic acids served as alkylating agents for the direct functionalization of representative polyaromatic hydrocarbons (PAHs) or benzene. The results are consistent with a free-radical mechanism.

A practical approach was developed for the synthesis of 4-arylquinazoline compounds through a one-pot nucleophilic arylation/alkylation of 2-chloroquinazoline with aryl lithium compounds generated in situ, followed by ring oxidation. The obtained 2-chloro-4-arylquinazoline adducts were further used as versatile intermediates that undergo a variety of synthetic transformations to provide functionalized quinazoline compounds. The arylation intermediate dihydroquinazoline was also elaborated to the tricyclic dihydroimidazo[2,1-b]quinazolinone.

An inter- as well as intra-molecular thia-Pictet–Spengler cyclization of N-tethered thiols and vinylogous thiocarbonates is described for the stereoselective synthesis of N-fused thiazinoindole derivatives. The strategy is extended to one-pot, sequential Friedel–Crafts alkylation – Pictet–Spengler cyclization and the synthesis of thiazino-oxepino-indole.

Protocol simplification is an important aspect in the development of organic reactions such as heteroarene functionalizations. An operationally facile protocol for the direct C–H alkylation of heteroarenes with unactivated ethers has been developed. The Minisci-type radical addition process involves thermolysis of potassium persulfate, circumventing the need for transition-metal catalysts.

A general regio- and stereoselective γ-C–C bond formation is achieved using α-halocarbonyl compounds and dienol ethers via Cu(II) catalysis. This method constitutes a novel approach to the challenging 1,6-dioxygenation motif. A range of γ-substituted enones, including many bearing all-carbon quaternary centers, are available through a simple protocol under mild reaction conditions with superb functional group compatibility. Excellent stereoinduction is observed providing controlled access to challenging stereochemical arrays.

The formation of the corresponding benzyl cations [ArHC+–CH(X)CF3] takes place under protonation of E-/Z-2-halogeno-2-CF3 styrenes [ArCH═C(X)CF3, X = F, Cl, Br] in superacids. The structures of these new electrophiles were studied by means of NMR and theoretical DFT calculations. According to these data, in the case of bromo derivatives, the formed cations, most probably, exist as cyclic bromonium ions; however, in the cases of chloro and fluoro derivatives, open forms are more preferable. Subsequent reaction of these benzyl cations with arenes proceeds as Friedel–Crafts alkylation to afford 1,1-diaryl-2-halo-3,3,3-trifluoropropanes [Ar(Ar′)CH–CH(X)CF3] in high yields (up to 96%) as a mixture of two diastereomers. The prepared halogenopropanes were easily converted into the corresponding mixtures of E-/Z-trifluoromethylated diarylethenes [Ar(Ar′)C═CCF3] (in yields up to 96%) by dehydrohalogenation with base (KOH or t-BuOK). The mechanism of elimination (E2 and Ecb) depends on the nature of the leaving gro...

The α-alkylation of unactivated amides with alcohols is described. Using a NCP-type pincer Ir complex as the precatalyst and KOtBu as the base, the reactions of secondary or tertiary acetamides with benzyl or nonbenzyl primary alcohols occur at 80 °C, furnishing the alkylation products in good yields. This method represents a practical and green means of α-alkylation of amides in a relatively mild, efficient, and selective manner with low catalyst loadings (0.5 mol %).

Recent developments in the photochemical carbon–carbon and carbon–heteroatom bond formation via photoinduced Ar–X bond dissociation are summarized. The transformations through the Ar–X bond dissociation enabled by photoenergy include nucleophilic substitution, arylation, alkylation, aminocarbonylation, aminosulfonylation and decarboxylative coupling reactions. Usually, the reactions undergo one-electron-transfer couplings and aryl radicals or cations are involved as the key intermediates. Under ultraviolet irradiation or visible light, the reactions of aryl halides with reactive partners proceed smoothly under mild conditions. In some cases, the transformations can proceed without any metals or photo-redox catalysts. Moreover, the broad reaction scope is demonstrated with good functional group tolerance.

The theoretical insights gained are experimentally examined performing an enantioselective oxocarbenium alkylation of α-chloroisochroman with silyl enolates.

A Pd-catalyzed alkylation of ortho C–H bonds in benzylamides possessing a bidentate-quinolinamide directing group with α-bromo ketones or nitrile is reported. α-Bromo aryl ketones, α-bromo alkyl ketone, and even α-bromo alkyl nitrile are competent reagents in this transformation, providing direct alkylated products with a pendant carbonyl or cyano group. Furthermore, direct alkylated products can be hydrolyzed under acidic conditions, providing a straightforward strategy for preparing high-value 3-arylisoquinoline derivatives.

Without using any additional ligands, RuCl3 efficiently catalyses the reductive N-alkylation of aryl nitro compounds with alcohols using bio-based glycerol as the hydrogen source and without the need for any added solvents. The reaction can be easily manipulated to produce either imines or secondary amines in high yields. RuCl3-catalyzed reductive N-alkylation of nitroarenes with alcohols affords the corresponding imine products in good to excellent yields. Under the same reaction conditions, the one-pot sequential reaction of nitroarenes with alcohols and glycerol also gives amines in higher yields.

A versatile diastereoselective Friedel-Crafts alkylation reaction of heteroaryl systems with a cyclic enecarbamate for the preparation of 5-heteroaryl-substituted proline analogues in good yields has been developed. These heterocyclic tethered cyclic amino acid building blocks constitute important structural motifs in many biologically active molecules. The impact of the substitution on proline cis/trans isomerization was explored by carrying out solution conformational studies by NMR on 5-furanyl-substituted proline-containing peptides. Conformational analysis revealed that the peptide bond is constrained in an exclusively trans conformation.

A novel organocatalyzed C–C bond-scission reaction of saturated aldehydes containing a suitable leaving group at the β-position was used for the in situ formation of iminium intermediates, which were then captured by nucleophiles to achieve a direct enantioselective β-alkylation of aldehydes. Within short reaction times, the corresponding β-alkylated aldehyde products were obtained in high yields (48–87%) and with excellent enantioselectivities (84–98%).

Whereas the stereochemical rigidity of the coordination sphere of boxmi/Cu(II) catalysts is key to achieving high enantioselectivity in the electrophilic alkylation of β-ketoesters, this pathway is outperformed by a radical process for the corresponding catalytic transformation of oxindoles, giving rise to racemic products. For the corresponding Zn(II) catalysts, the selectivity in the latter process is outstanding despite the greater plasticity of the coordination shell. This reaction was thus developed into a highly useful synthetic method, which enabled the conversion of wide range of substrates with high yields and enantioselectivities.

Previous work has demonstrated that alkylated benzene sulfonanilides undergo sulfuric acid (98%)–catalyzed rearrangement to alkylamino diaryl sulfones. Similar treatment of their unalkylated analogs typically leads only to hydrolysis. Surprisingly, when the unalkylated benzene sulfonanilides react with triflic acid, rearrangement to sulfones does occur.

Transition-metal-catalyzed asymmetric allylic alkylation of enolates is a powerful method for the formation of carbon− carbon bonds. Within this field, palladium-catalyzed allylic alkylation reactions have undoubtedly been the most studied. Aside from limited cases, palladium catalysts preferentially form the linear substitution product through alkylation at the less-substituted terminus of the allylic electrophile (Scheme 1). However, in contrast to palladium, most other transition metals (e.g., Mo, W, Fe, Ru, Co, Rh, Ni, Pt, and Ir) have been shown to favor the construction of the branched product, with iridium catalysts being some of the most efficient and selective. The potential application of these chiral, branched products to the synthesis of natural products and biologically active compounds has motivated the development of practical and reliable transition-metal-catalyzed methods for their construction.

A palladium-catalyzed ortho-directed alkylation of O-methyl ketoximes that proceeds through a regioselective ring-opening reaction of epoxides has been demonstrated. This C(sp2)–H activation/alkylation protocol was carried out in pivalic acid/1,1,1,3,3,3-hexafluoro-2-propanol (PivOH/HFIP, 2:8) as the solvent and was applied to various O-methyl ketoximes that contain either electron-donating or electron-withdrawing groups. Moreover, different types of epoxides were used in this alkylation reaction, which proceeded smoothly to give the corresponding products in moderate to good yields.

Although visible light photoredox catalysis has emerged as a powerful tool for the construction of C–C bonds, common catalysts and/or their photoexcited states suffer from low redox potentials, limiting their applicability to alkyl radical generation from substrates with activated carbon–halogen bonds. Radicals derived from these activated compounds, being highly electrophilic or stabilized, do not undergo efficient addition to heteroarenes. Herein we describe the photocatalytic generation of nucleophilic alkyl radicals from unactivated bromoalkanes as part of a universal and efficient cross-coupling strategy for the direct alkylation of heteroarenes using a dimeric gold(I) photoredox catalyst, [Au2(bis(diphenylphosphino)methane)2]Cl2. The method proves to be efficient for alkylation of arenes under mild conditions in the absence of directing groups.

In this Digest Letter, we collected and shortly summarized the recently developed dual transition metal–visible light photoredox catalytic processes including arylation, alkynylation, alkenylation, allylation, alkylation, fluoroalkylation, benzylation, acylation, and cyclization reactions. The utilization of multimetallic catalytic systems provides new synthetic strategies for the synthesis and functionalization of versatile and novel organic compounds.

A catalytic, enantioselective γ-alkylation of α,β-unsaturated malonates and ketoesters is reported. This strategy entails a highly regio- and enantioselective iridium-catalyzed α-alkylation of an extended enolate, and a subsequent translocation of chirality to the γ-position via a Cope rearrangement.

The first synthesis of decursivine derivatives of coumarins is described via intramolecular Friedel–Craft aromatic alkylation. The Lewis acid (LA)–catalyzed reaction facilitated the rapid construction of the desired product. The targeted molecule obtained has been confirmed by spectral analysis.

We report nickel-catalyzed cross-coupling of methoxyarenes with alkylmagnesium halides, in which a methoxy group is eliminated. A wide range of alkyl groups, including those bearing β-hydrogens, can be introduced directly at the ipso position of anisole derivatives. We demonstrate that the robustness of a methoxy group allows this alkylation protocol to be used to synthesize elaborate molecules by combining it with traditional cross-coupling reactions or oxidative transformation. The success of this method is dependent on the use of alkylmagnesium iodides, but not chlorides or bromides, which highlights the importance of the halide used in developing catalytic reactions using Grignard reagents.