Electrophilic Partners Research Articles

1,2-Difunctionalization of Aryl Triflates: A Direct and Modular Access to Diversely Functionalized Anilines.

ortho-Amino difunctionalization of aryl triflates has been achieved via a three-component reaction. The cascade reaction proceeds through a zincate base-mediated deprotonative formation of a reactive aryne intermediate, in situ nucleophilic addition, and coupling with electrophilic partners. This strategy leverages the advantageous reactivity of organozincate intermediates, enabling the installation of various functionalities such as amine, azide, oxygen, sulfur, halide, alkynyl, aryl, vinyl, and alkyl groups in a modular manner for the synthesis of diverse aniline skeletons.

Site-Selective 1,2-Dicarbofunctionalization of Vinyl Boronates through Dual Catalysis.

A modular, site-selective 1,2-dicarbofunctionalization of vinyl boronates with organic halides through dual catalysis is described. This reaction proceeds under mild conditions and is characterized by excellent chemo- and regioselectivity. It thus represents a complementary new technique for preparing densely functionalized alkyl boron architectures from simple and accessible precursors.

Expansion of annulation of allenoates with trifluoroketones: Synthesis of trifluoromethylated dihydropyrans

The DABCO-catalyzed [2 + 2] annulation of allenoates with trifluoroketones could be expanded to [4 + 2] annulation to synthesize trifluoromethylated dihydropyrans with trifluoromethyl oxadienes as the electrophilic annulation partners.

Vinyl‐/Furoindoles and Gold Catalysis: New Achievements and Future Perspectives for the Synthesis of Complex Indole Derivatives

The reactivity of vinyl‐/furoindole derivatives with gold‐activated π‐systems is the subject of extensive investigation. In the presence of these electrophilic partners, the realized transformations allow for the construction of different and fascinating architectures via cycloaddition and cyclization reactions often included in cascade processes. The reactions realized involving in these processes an external substituent at the indole moiety are the subject of the present minireview.

Aryl Azides as Forgotten Electrophiles in the Van Leusen Reaction: A Multicomponent Transformation Affording 4-Tosyl-1-arylimidazoles.

Considering aryl azides as electrophilic partners for the TosMIC mediated Van Leusen reaction, a novel multicomponent synthesis of 4-tosyl-1-arylimidazoles is reported. In this transformation, two molecules of TosMIC participate in the reaction mechanism in two different ways, with the second molecule undergoing a novel type of fragmentation resulting in the incorporation of a C-H into the final product.

Cascade Cross-Coupling of Dienes: Photoredox and Nickel Dual Catalysis.

Chemical transformations based on cascade reactions have the potential to simplify the preparation of diverse and architecturally complex molecules dramatically. Herein, we disclose an unprecedented and efficient method for the cross‐coupling of radical precursors, dienes, and electrophilic coupling partners via a photoredox‐ and nickel‐enabled cascade cross‐coupling process. The cascade reaction furnishes a diverse array of saturated carbo‐ and heterocyclic scaffolds, thus providing access to a quick gain in C−C bond saturation.

Cascade Cross‐Coupling of Dienes: Photoredox and Nickel Dual Catalysis

AbstractChemical transformations based on cascade reactions have the potential to simplify the preparation of diverse and architecturally complex molecules dramatically. Herein, we disclose an unprecedented and efficient method for the cross‐coupling of radical precursors, dienes, and electrophilic coupling partners via a photoredox‐ and nickel‐enabled cascade cross‐coupling process. The cascade reaction furnishes a diverse array of saturated carbo‐ and heterocyclic scaffolds, thus providing access to a quick gain in C−C bond saturation.

Redox-Selective Iron Catalysis for α-Amino C-H Bond Functionalization via Aerobic Oxidation.

Single-electron oxidation and α-deprotonation of tertiary anilines using Fe(phen)3(PF6)3 afford α-aminoalkyl radicals, which can be coupled with electrophilic partners to afford various tetrahydroquinolines. Mechanistically, the Fe(phen)n2+/3+ catalytic cycle is maintained by O2 or a TBHP oxidant, and the presence of the oxygen bound iron complex, Fe(III)-OO(H), was elucidated by electron paramagnetic resonance and electrospray ionization mass spectrometry. This redox-selective nonheme iron catalyst behaves similarly to bioinspired heme iron catalysts.

Rhodium(I)/Zn(OTf)2 -Catalyzed Asymmetric Ring Opening/Cyclopropanation of Oxabenzonorbornadienes with Phosphorus Ylides.

The strong binding ability of P-ylides with transition metals limits the utilization of stabilized P-ylide as nucleophiles in asymmetric organometallic catalysis. Herein we describe the first rhodium-catalyzed asymmetric ring-opening reaction of P-ylides utilizing oxabicyclic alkenes as the electrophilic partner. Various P-ylides including ester-, ketone- and amide-style P-ylides are all applicable. This asymmetric reaction occurs through the cleavage of two bridgehead C-O bonds and the formation of two C-C bonds, and oxabenzonorbornadienes are used as 1,4-biselectrophiles, thus providing access to benzonorcaradienes in good yields with high enantioselectivity and perfect diastereoselectivity. The present protocol also constitutes the first highly enantioselective direct catalytic asymmetric cyclopropanation of stabilized P-ylide nucleophiles.

Rhodium(I)/Zn(OTf)2‐Catalyzed Asymmetric Ring Opening/Cyclopropanation of Oxabenzonorbornadienes with Phosphorus Ylides

AbstractThe strong binding ability of P‐ylides with transition metals limits the utilization of stabilized P‐ylide as nucleophiles in asymmetric organometallic catalysis. Herein we describe the first rhodium‐catalyzed asymmetric ring‐opening reaction of P‐ylides utilizing oxabicyclic alkenes as the electrophilic partner. Various P‐ylides including ester‐, ketone‐ and amide‐style P‐ylides are all applicable. This asymmetric reaction occurs through the cleavage of two bridgehead C−O bonds and the formation of two C−C bonds, and oxabenzonorbornadienes are used as 1,4‐biselectrophiles, thus providing access to benzonorcaradienes in good yields with high enantioselectivity and perfect diastereoselectivity. The present protocol also constitutes the first highly enantioselective direct catalytic asymmetric cyclopropanation of stabilized P‐ylide nucleophiles.

Suzuki-Miyaura Coupling of (Hetero)Aryl Sulfones: Complementary Reactivity Enables Iterative Polyaryl Synthesis.

Ideal organic syntheses involve the rapid construction of C-C bonds, with minimal use of functional group interconversions. The Suzuki-Miyaura cross-coupling (SMC) is a powerful way to form biaryl linkages, but the relatively similar reactivity of electrophilic partners makes iterative syntheses involving more than two sequential coupling events difficult to achieve without additional manipulations. Here we introduce (hetero)aryl sulfones as electrophilic coupling partners for the SMC reaction, which display an intermediate reactivity between those of typical aryl (pseudo)halides and nitroarenes. The new complementary reactivity allows for rapid sequential cross-coupling of arenes bearing chloride, sulfone and nitro leaving groups, affording non-symmetric ter- and quateraryls in only 2 or 3 steps, respectively. The SMC reactivity of (hetero)aryl sulfones is demonstrated in over 30 examples. Mechanistic experiments and DFT calculations are consistent with oxidative addition into the sulfone C-S bond as the turnover-limiting step. The further development of electrophilic cross-coupling partners with complementary reactivity may open new possibilities for divergent iterative synthesis starting from small pools of polyfunctionalized arenes.

Suzuki–Miyaura Coupling of (Hetero)Aryl Sulfones: Complementary Reactivity Enables Iterative Polyaryl Synthesis

AbstractIdeal organic syntheses involve the rapid construction of C−C bonds, with minimal use of functional group interconversions. The Suzuki–Miyaura cross‐coupling (SMC) is a powerful way to form biaryl linkages, but the relatively similar reactivity of electrophilic partners makes iterative syntheses involving more than two sequential coupling events difficult to achieve without additional manipulations. Here we introduce (hetero)aryl sulfones as electrophilic coupling partners for the SMC reaction, which display an intermediate reactivity between those of typical aryl (pseudo)halides and nitroarenes. The new complementary reactivity allows for rapid sequential cross‐coupling of arenes bearing chloride, sulfone and nitro leaving groups, affording non‐symmetric ter‐ and quateraryls in only 2 or 3 steps, respectively. The SMC reactivity of (hetero)aryl sulfones is demonstrated in over 30 examples. Mechanistic experiments and DFT calculations are consistent with oxidative addition into the sulfone C−S bond as the turnover‐limiting step. The further development of electrophilic cross‐coupling partners with complementary reactivity may open new possibilities for divergent iterative synthesis starting from small pools of polyfunctionalized arenes.

Oxa- and Azabenzonorbornadienes as Electrophilic Partners under Photoredox/Nickel Dual Catalysis.

Herein, the introduction of oxa- and azabenzonorbornadienes into photoredox/nickel dual catalysis in a regioselective and diastereoselective transformation is disclosed. The inherent advantages of this dual catalytic system allow the use of alkyl motifs forming exclusively cis-1,2-dihydro-1-naphthyl alcohol backbones using readily accessible 4-alkyl-1,4-dihydropyridines (DHPs). Whereas previous studies have emphasized the use of nucleophilic organometallic coupling partners, this protocol grants access to a rather unexplored core featuring alkyl residues, while avoiding the use of highly reactive organometallic species (i.e., M = Al, Mg, Li, Zn, Zr). DFT calculations support a oxidative addition/reductive elimination mechanism, followed by a Curtin-Hammett scenario that controls the regioselectivity of the process, unlike previously reported transformations that proceed via a carbometalation/ β-oxygen elimination mechanism.

Protocols for the Syntheses of 2,2′-Bis(indolyl)arylmethanes, 2-Benzylated Indoles, and 5,7-Dihydroindolo[2,3-b]carbazoles

The electrophilic substitution reaction of 4,7-dihydroindole with aryl-aldehydes as an electrophilic partner followed by an oxidation step to deliver 2,2'-bis(indolyl)arylmethanes was studied for the first time. The reaction afforded regioselectivity at the 2,2'-positions of indole in an operationally simple and inexpensive procedure with a variety of substrates. To the best of our knowledge, this is the first set of examples of 2,2'-bis(indolyl)arylmethanes obtained in a substituent-free manner. A facile method from dipyrromethanes to the corresponding 2-benzylindoles was also reported. In addition, 2,2'-bis(indolyl)arylmethanes were converted to 5,7-dihydroindolo[2,3-b]carbazoles.

SYNTHESIS OF INDIVIDUAL ISOMERS OF 2-(3-CHLOROPROP-2-EN-1-YL)CYCLOHEXANONE

Recently, vinyl chlorides has been increasingly used as electrophilic partners in various cross-coupling reactions. In contrast to inaccessible and expensive vinyl bromides and iodides, in many cases vinyl chlorides are highly active in the presence of not only traditional palladium complexes, but also economical and safe compounds of iron, cobalt and nickel. Earlier, we reported on the development of new approaches to the getting of stereochemically pure (E)- and (Z)-vinyl chlorides and their successful use at the synthesis of medicines and insect pheromones. Continuing this work, an effective method of the synthesis of (E)- and (Z)-isomers of 2-(3-chloroprop-2-en-1-yl)cyclohexanone - convenient precursors of 2-(alk-2-en-1-yl)cyclohexanones, known flavors and intermediates in the synthesis of polycyclic compounds was developed. In the reaction of ethyl 2-oxocyclohexanecarboxylate with the (E)- and (Z)-isomers of 1,3-dichloropropene under the phase-transfer catalysis conditions in the presence of K2CO3, the corresponding (E)- and (Z)-isomers of ethyl 1-(3-chloroprop-2-en-1-yl)-2-oxocyclohexanecarboxylate were obtained in high yields (80-86%), without allyl rearrangement. The complete retention of the configuration of the chlorovinyl group is observed. Standard methods of the decarboxylation of isomers of ethyl 1-(3-chloroprop-2-en-1-yl)-2-oxocyclohexanecarboxylate under acidic or basic conditions result in very average yields of the corresponding chlorovinyl ketones. The best results were obtained by their decarbalkoxylation in slightly modernized Krapcho conditions. Carrying out reaction in N-methylpyrrolidone at 140-150 °C in the presence of 3 eq. LiCl and 2 eq. of H2O leads to individual (E)- and (Z)-isomers of 2-(3-chloroprop-2-en-1-yl)cyclohexanone in 79-82% yields and a stereochemical purity of ~ 99%. The structure of the obtained compounds were confirmed by HRGC, NMR, and GC/MS data. The configuration of the vinyl group was proved by the coupling constants of the vinyl hydrogens, equal to 13.2-13.4 and 7.0-7.3 Hz for the (E)- and (Z)-products, respectively, as well as by the downfield shift of the allyl carbon atom of trans-isomers by ~4 ppm as compared to the cis-analogs.

Well-Designed N-Heterocyclic Carbene Ligands for Palladium-Catalyzed Denitrative C–N Coupling of Nitroarenes with Amines

The C–N bond formation is one of the fundamental reactions in organic chemistry, because of the widespread presence of amine moieties in pharmaceuticals and biologically active compounds. Palladium-catalyzed C–N coupling of haloarenes represents one of the most efficient approaches to aromatic amines. Nitroarenes are ideal alternative electrophilic coupling partners, since they are inexpensive and readily available. The denitration and cross-coupling using nitroarenes as the electrophilic partners is challenging, because of the low reactivity of the Ar–NO2 bond toward oxidative addition. We report here the C–N coupling of nitroarenes and amines using palladium/5-(2,4,6-triisopropylphenyl)imidazolylidene[1,5-a]pyridines as the catalyst. The ligands are readily available from commercial chemicals. The reaction shows broad substrate scope and functional group tolerance. The method is applicable to both aromatic and aliphatic amines, and many secondary and tertiary aromatic amines bearing various functional g...

Cross-Coupling of Heteroatomic Electrophiles

At the advent of cross-coupling chemistry, carbon electrophiles based on halides or pseudohalides were the only suitable electrophilic coupling partners. Almost two decades passed before the first cross-coupling reaction of heteroatom-based electrophiles was reported. Early work by Murai and Tanaka initiated investigations into silicon electrophiles. Narasaka and Johnson pioneered the way in the use of nitrogen electrophiles, while Suginome began the exploration of boron electrophiles. The chemistry reviewed within provides perspective on the use of heteroatomic electrophiles, specifically silicon-, nitrogen-, boron-, oxygen-, and phosphorus-based electrophiles in transition-metal catalyzed cross-coupling. For the purposes of this review, a loose definition of cross-coupling is utilized; all reactions minimally proceed via an oxidative addition event. Although not cross-coupling in a traditional sense, we have also included catalyzed reactions that join a heteroatomic electrophile with an in situ generated nucleophile. However, for brevity, those involving hydroamination or C-H activation as a key step are largely excluded. This work includes primary references published up to and including October 2018.

Nickel-catalyzed Suzuki\u2013Miyaura cross-couplings of aldehydes

Transition-metal-catalyzed cross-couplings have been extensively used in the pharmaceutical and agrochemical industries for the construction of diverse C–C bonds. Conventional cross-coupling reactions require reactive electrophilic coupling partners, such as organohalides or sulfonates, which are not environmentally friendly and not naturally abundant. Another disadvantage associated with these transformations is the need for an exogenous base to facilitate the key transmetalation step, and this reagent inevitably induces side reactions and limits the substrate scope. Here, we report an unconventional Suzuki-type approach to the synthesis of biaryls, through nickel-catalyzed deformylative cross coupling of aldehydes with organoboron reagents under base-free conditions. The transformation tolerates structurally diverse (hetero)aryl substituents on both coupling partners and shows high reactivity and excellent functional group tolerance. Furthermore, the protocol was carried out on gram scale and successfully applied to the functionalization of complex biologically active molecules. Mechanistic investigations support a catalytic cycle involving the oxidative addition of the nickel into the aldehyde C(acyl)–H bond with subsequent hydride transfer, transmetalation, decarbonylation and reductive elimination processes.

Recent progress in transition metal catalyzed cross coupling of nitroarenes

In this review, the recent development in transition metal catalyzed cross coupling of nitroarenes was highlighted. Firstly, development of transition metal catalyzed cross coupling was simply introduced. After presenting the advantages of nitroarenes, transition metal catalyzed cross coupling using nitroarenes as electrophilic coupling partners was classified and introduced in detail. Based on different chemical bonds such as C–O, C–S, CC and C–N bonds constructed, different kinds cross coupling of nitroarenes would be highlighted and the plausible reaction mechanism would be presented if available.

Sonogashira Cross-Coupling of Aryltrimethylammonium Salts

A protocol for C(sp)–C(sp2) bond formation via the Sonogashira coupling reaction involving C–N bond cleavage with aryltrimethylammonium triflate as an electrophilic coupling partner is described in...