Superacid-Catalyzed Reactions of Cinnamic Acids and the Role of Superelectrophiles1

Synthesis of tetralone and indanone derivatives via cascade reductive Friedel-Crafts alkylation/cyclization of keto acids/esters

We disclose herein a metal-free cascade reductive Friedel-Crafts alkylation/cyclization of keto acids/esters for the synthesis of tetralones and indanones. Owing to the simple reaction conditions and setup, this protocol features broad substrate generality, facile scalability, and remarkable functional group tolerance, including the synthesis of bioactive molecule sertraline.

Silver-Promoted Rapid Synthesis of 3-Arylindan-1-ones: Microwave-Assisted Reductive Coupling of N-Tosylhydrazone and Boronic Acids

An efficient and straightforward one-pot tandem synthesis of 3-arylindan-1-ones was consummated through silver nitrate-promoted C-C coupling of simple indane-1,3-dione with arylboronic acid via 1,3-indanedione monotosylhydrazone under microwave conditions. The resulting series of 3-arylindan-1-ones exhibited impressive yields, surpassing those achievable with traditional methods and requiring a shorter time frame. This innovative approach significantly accelerated the synthesis of biologically active compounds such as (+)-indatraline (Lu 19-005) and several other industrially relevant substances.

The Use of Aryl-Substituted Homophthalic Anhydrides in the Castagnoli-Cushman Reaction Provides Access to Novel Tetrahydroisoquinolone Carboxylic Acid Bearing an All-Carbon Quaternary Stereogenic Center

Novel aryl-substituted homophthalic acids were cyclodehydrated to the respective homophthalic anhydrides for use in the Castagnoli-Cushman reaction. With a range of imines, this reaction proceeded smoothly and delivered hitherto undescribed 4-aryl-substituted tetrahydroisoquinolonic acids with remarkable diastereoselectivity, good yields and no need for chromatographic purification. These findings significantly extend the range of cyclic anhydrides employable in the Castagnoli-Cushman reaction and signify access to a novel substitution pattern around the medicinally relevant tetrahydroisoquinolonic acid scaffold.

5,5,5-Trichloropent-3-en-one as a Precursor of 1,3-Bi-centered Electrophile in Reactions with Arenes in Brønsted Superacid CF3SO3H. Synthesis of 3-Methyl-1-trichloromethylindenes

Reactions of 5,5,5-trichloropent-3-en-2-one Cl₃CCH=CHC(=O)Me with arenes in Brønsted superacid CF₃SO₃H at room temperature for 2 h-5 days afford 3-methyl-1-trichloromethylindenes, a novel class of indene derivatives. The key reactive intermediate, O-protonated form of starting compound Cl₃CCH=CHC(=OH⁺)Me, has been studied experimentally by NMR in CF₃SO₃H and theoretically by DFT calculations. The reaction proceeds through initial hydroarylation of the carbon-carbon double bond of starting CCl₃-enone, followed by cyclization onto the O-protonated carbonyl group, leading to target indenes. In general, 5,5,5-trichloropent-3-en-2-one in CF₃SO₃H acts as a 1,3-bi-centered electrophile.

Friedel-Crafts-Type Acylation and Amidation Reactions in Strong Brønsted Acid: Taming Superelectrophiles

In this review, we discuss Friedel-Crafts-type aromatic amidation and acylation reactions, not exhaustively, but mainly based on our research results. The electrophilic species involved are isocyanate cation and acylium cation, respectively, and both have a common ⁺C=O structure, which can be generated from carboxylic acid functionalities in a strong Brønsted acid. Carbamates substituted with methyl salicylate can be easily ionized to the isocyanate cation upon (di)protonation of the salicylate. Carboxylic acids can be used directly as a source of acylium cations. However, aminocarboxylic acids are inert in acidic media because two positively charged sites, ammonium and acylium cation, will be generated, resulting in energetically unfavorable charge-charge repulsion. Nevertheless, the aromatic acylation of aminocarboxylic acids can be achieved by using tailored phosphoric acid esters as Lewis bases to abrogate the charge-charge repulsion. Both examples tame the superelectrophilic character.

DFT insights into superelectrophilic activation of α,β-unsaturated nitriles and ketones in superacids

Superelectrophilic activation of α,β-unsaturated carbonyl compounds and their isoelectronic analogs, proceeding normally under superacidic conditions, have led to a great variety of beneficial synthetic transformations. However, the essence of such activation is not yet fully recognized, while a number of alternative views on the subject have been discussed at length in the literature. Here, taking the example of virtual reactions of cinnamonitrile and benzalacetone with benzene, their feasible mechanistic variants, including multiple protonation (coordination to AlCl₃) of the reactants, were analyzed based on density functional theory (DFT). It is revealed that the most plausible reaction pathways involve the initial N- or O-protonation (coordination to AlCl₃) of the activated compounds followed by subsequent protonation on the α-C-atom. Dicationic superelectrophiles thus formed ensure practically barrier-free reactions with benzene in addition to a more favorable energetic profile of their generating, which is in marked contrast to other potential reaction pathways.

Synthesis of 3-Aryl-3-(Furan-2-yl)Propanoic Acid Derivatives, and Study of Their Antimicrobial Activity

Reactions of 3-(furan-2-yl)propenoic acids and their esters with arenes in Brønsted superacid TfOH affords products of hydroarylation of the carbon–carbon double bond, 3-aryl-3-(furan-2-yl)propenoic acid derivatives. According to NMR and DFT studies, the corresponding O,C-diprotonated forms of the starting furan acids and esters should be reactive electrophilic species in these transformations. Starting compounds and their hydroarylation products, at a concentration of 64 µg/mL, demonstrate good antimicrobial activity against yeast-like fungi Candida albicans. Apart from that, these compounds suppress Escherichia coli and Staphylococcus aureus.

Reactions of linear conjugated dienone structures with arenes under superelectrophilic activation conditions. An experimental and theoretical study of intermediate multicentered electrophilic species

Reactions of conjugated dienones with arenes under superelectrophilic activation conditions result in the formation of conjugated enones, indanes, and carbocyclic structures.

Exploring the synthetic potential of a marine transaminase including discrimination at a remote stereocentre

The marine transaminase, P-ω-TA, can be employed for the transamination from 1-aminotetralins and 1-aminoindanes with differentiation of stereochemistry at both the site of reaction and at a remote stereocentre resulting in formation of ketone products with up to 93% ee. While 4-substituents are tolerated on the tetralin core, the presence of 3- or 8-substituents is not tolerated by the transaminase. In general P-ω-TA shows capacity for remote diastereoselectivity, although both the stereoselectivity and efficiency are dependent on the specific substrate structure. Optimum efficiency and selectivity are seen with 4-haloaryl-1-aminotetralins and 3-haloaryl-1-aminoindanes, which may be associated with the marine origin of this enzyme.

Efficient kinetic resolution in the asymmetric transfer hydrogenation of 3-aryl-indanones: applications to a short synthesis of (+)-indatraline and a formal synthesis of (R)-tolterodine

Efficient kinetic resolution occurs in ATH of racemic 3-arylindanones using (R,R)-or (S,S)-Ts-DENEB catalyst and HCO₂H/Et₃N mixture providing near equal yields of cis-3-arylindanols and unreacted 3-arylindanones with excellent stereoselectivities.

Rh-Catalyzed Annulation of Benzoic Acids, Formaldehyde, and Malonates via ortho-Hydroarylation to Indanones

A three-component reaction from readily available low-cost materials of benzoic acids, formaldehyde, and malonates for the preparation of indanones by rhodium catalysis is reported. The annulation is initiated by an ortho-hydroarylation of benzoic acids, and a Lewis acid is not required. The solvent has a significant influence to the reaction, and 2-substituted or nonsubstituted indanones are obtained by the change of solvent.

Rhodium(iii)-catalyzed synthesis of 3-trifluoromethylindanones from N-methoxybenzamides via C–H activation and Claisen/retro-Claisen reaction

An efficient synthesis of 3-trifluoromethylindanones via C–H annulation of N-methoxybenzamides with β-trifluoromethyl-α,β-unsaturated ketones under Rh(iii)-catalysis is described.

Solventless Wittig Olefination with Fluorinated Benzaldehydes

Fluorinated benzaldehydes undergo solventless Wittig olefination with stabilised phosphoranes. Even with less reactive, stabilised phosphoranes, such as acetylmethylidenetriphenylphosphorane, the reactions have been found to be exothermic.

Synthesis of 3-Aryl-1-Indanones via CsF-Promoted Coupling of Arylboronic Acids with N-Tosylhydrazones

A series of 173-aryl-1-indanones, four of which are novel, were prepared in good yield via a CsF-promoted reductive cross-coupling of the monotosylhydrazone of a 1,3-indanedione with an arylboronic acid. The method demonstrates wide substrate scope and good functional group tolerance. Moreover, the 3-aryl-1-indanones could also be prepared on a multi-gram scale.

Catalysis of photooxidation reactions through transformation between Cu2+ and Cu+ in TiO2–Cu–MOF composites

Novel porous TiO₂@Cu₃(BTC)₂ composites, which were synthesized using ionic liquids (ILs) as solvents, exhibited excellent activity for photooxidation of styrene to 4-aryl tetralones and promoting the Glaser coupling reaction with O₂ under light irradiation.

Facile synthesis of 2,3-benzodiazepines using one-pot two-step phosphate-assisted acylation–hydrazine cyclization reactions

We present a one-pot two-step methodology, in which an unprotected amino is tolerated, for rapidly synthesizing 2,3-benzodiazepines via phosphate-assisted acylation reaction and hydrazine cyclization reaction.

Friedel-Crafts Acylation Reactions of BN-Substituted Arenes

The acylation reaction of BN-arenes has been studied using BN-arene and acyl chloride in good to excellent yields, which led to the first synthesis of indanone BN-analogue. The BN-aromatic ketone products have been characterized by ¹H NMR spectroscopy with their molecular structures unambiguously confirmed by X-ray crystallography. The annulation reaction of BN-arenes promoted by AgBF₄ occurs in a completely regioselective manner and a mechanism for this transformation is proposed.

Sustainable synthesis of 3-substituted phthalides via a catalytic one-pot cascade strategy from 2-formylbenzoic acid with β-keto acids in glycerol

Background: Phthalides are privileged constituents of numerous pharmaceuticals, natural products and agrochemicals and exhibit several biological and therapeutic activities. Therefore, the development of new, facile, and sustainable strategies for the construction of these moieties is highly desired.

Results: A broad substrate scope for β-keto acids was found to be strongly compatible with this catalytic process, affording a wide variety of 3-substituted phthalides in good to excellent yields.

Conclusion: A concise and efficient synthesis strategy of 3-substituted phthalides from 2-formylbenzoic acid and β-keto acids via a catalytic one-pot cascade reaction in glycerol has been accomplished.

Metal-free hydroarylation of the side chain carbon-carbon double bond of 5-(2-arylethenyl)-3-aryl-1,2,4-oxadiazoles in triflic acid

The metal-free reaction of 5-(2-arylethenyl)-3-aryl-1,2,4-oxadiazoles with arenes in neat triflic acid (TfOH, CF3SO3H), both under thermal and microwave conditions, leads to 5-(2,2-diarylethyl)-3-aryl-1,2,4-oxadiazoles. The products are formed through the regioselective hydroarylation of the side chain carbon-carbon double bond of the starting oxadiazoles in yields up to 97%. According to NMR data and DFT calculations, N4,C-diprotonated forms of oxadiazoles are the electrophilic intermediates in this reaction.

Chemoselective generation of acyl phosphates, acylium ion equivalents, from carboxylic acids and an organophosphate ester in the presence of a Brønsted acid

Reactions of an organophosphate ester with carboxylic acids proceeded smoothly and chemoselectively in the presence of a Brønsted acid, affording acyl phosphate intermediates, leading to formation of various functional aromatic ketones.

Rhodium(iii)-catalyzed synthesis of indanones via C–H activation of phenacyl phosphoniums and coupling with olefins

Phosphonium ylide acts as an efficient directing group in the oxidative carbocyclization between arenes and activated olefins for indanone synthesis.

Superelectrophilic activation of 5-hydroxymethylfurfural and 2,5-diformylfuran: organic synthesis based on biomass-derived products

The reaction of 5-hydroxymethylfurfural (5-HMF) with arenes in superacidic trifluoromethanesulfonic acid (triflic acid, TfOH) as the solvent at room temperature for 1–24 h gives rise to 5-arylmethylfurfurals (yields of 17–91%) and 2-arylmethyl-5-(diarylmethyl)furans (yields of 10–37%). The formation of these two types of reaction products depends on the nucleophilicity of the arene. The same reactions under the action of acidic zeolites H-USY in high pressure tubes at 130 °C for 1 h result in the formation of only 5-arylmethylfurfurals (yields of 45–79%). 2,5-Diformylfuran (2,5-DFF) in the reaction with arenes under the action of AlBr₃ at room temperature for 1 h leads to 5-(diarylmethyl)furfurals (yields of 51–90%). The reactive protonated species of 5-HMF and 2,5-DFF were characterized by NMR spectroscopy in TfOH and studied by DFT calculations. These reactions show possibilities of organic synthesis based on biomass-derived 5-HMF and 2,5-DFF.

Synthesis and Spectral Characterization of Benzo-[6,7][1,5]diazocino[2,1-a]isoindol-12-(14H)-one Derivatives

A simple synthetic route affording 27%–85% yields of benzo[6,7][1,5]diazocino[2,1-a]isoindol-12(14H)-one ring systems from readily available 3-(2-oxo-2-phenylethyl) isobenzofuran-1(3H)-ones and 2-(aminomethyl)aniline starting materials in toluene and catalysed by p-toluene-sulfonic acid is developed. The ¹H- and ¹³C-NMR spectra of the final products were assigned using a variety of one and two-dimensional NMR experiments. The distinction between the two potential isomers of the final products was made on the basis of heteronuclear multiple bond connectivity (HMBC) NMR spectra.

Friedel-Crafts Alkylation of Arenes with 2-Halogeno-2-CF3-styrenes under Superacidic Conditions. Access to Trifluoromethylated Ethanes and Ethenes

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 group and reaction conditions.

Tandem buildup of complexity of aromatic molecules through multiple successive electrophile generation in one pot, controlled by varying the reaction temperature

While some sequential electrophilic aromatic substitution reactions, known as tandem/domino/cascade reactions, have been reported for the construction of aromatic single skeletons, one of the most interesting and challenging possibilities remains the one-pot build-up of a complex aromatic molecule from multiple starting components, i.e., ultimately multi-component electrophilic aromatic substitution reactions. In this work, we show how tuning of the leaving group ability of phenolate derivatives from carbamates and esters provides a way to successively generate multiple unmasked electrophiles in a controlled manner in one pot, simply by varying the temperature. Here, we demonstrate the autonomous formation of up to three bonds in one pot and formation of two bonds arising from a three-component electrophilic aromatic substitution reaction. This result provides a proof-of-concept of our strategy applicable for the self-directed construction of complex aromatic structures from multiple simple molecules, which can be a potential avenue to realize multi-component electrophilic aromatic substitution reactions.

Electronic effects of substituents on the stability of the iridanaphthalene compound [Ir[upper bond 1 start]Cp*{=C(OMe)CH=C(o-C6[upper bond 1 end]H4)(Ph)}(PMe3)]PF6

Iridanaphthalene complexes are synthesized from the corresponding methoxy(alkenyl)carbeneiridium compounds. The electronic character of the substituents on the 6-position of the metallanaphthalene ring is crucial from the point of view of the stability of the iridanaphthalene, [Ir[upper bond 1 start]Cp*{=C(OMe)CH=C(o-C[upper bond 1 end]6H4)(Ph)}(PMe3)]PF6, vs. its transformation to the corresponding indanone derivatives. Stability studies of the iridanaphthalene compounds revealed that strong electron donor substituents (-OMe) stabilize the iridanaphthalene, while weak electron donor (-Me) and electron withdrawing (-NO2) groups favor the formation of indanone derivatives. Two possible indanone isomers can be obtained in the conversion of the unstable iridanaphthalene complexes and a mechanism for the formation of these isomers is proposed.

1-Methyl-3-(propyl-3-sulfonic acid)imidazolium triflate supported on magnetic nanoparticles: an efficient and reusable catalyst for synthesis of mono- and bis-isobenzofuran-1(3H)-ones under solvent-free conditions

An efficient procedure for the synthesis of isobenzofuran-1(3H)-one derivatives in the presence of [HSO₃PMIM]OTf–SiO₂@MNPs as a highly recyclable catalyst under solvent-free thermal conditions and MW irradiation is reported.

Reactions of CF3-enones with arenes under superelectrophilic activation: a pathway to trans-1,3-diaryl-1-CF3-indanes, new cannabinoid receptor ligands

CF₃-enones react with arenes in TfOH to givetrans-1,3-diaryl-1-CF₃indanes.

Indium-catalyzed, novel route to β,β-disubstituted indanones via tandem Nakamura addition–hydroarylation–decarboxylation sequence

An indium-catalyzed, novel method for the generation of β,β-disubstituted indanones was described. Indium(iii) trifluoromethanesulfonate is reported as the multitasking catalyst that promotes tandem Nakamura addition–hydroarylation–decarboxylation process under one-pot conditions.

Superacid mediated intramolecular condensation: facile synthesis of indenones and indanones

Superacid promoted intramolecular acylation is described for the synthesis of indenones.

(CF3CO)2O/CF3SO3H-mediated synthesis of 1,3-diketones from carboxylic acids and aromatic ketones

A very simple and convenient reaction for 1,3-diketone preparation from carboxylic acids and aromatic ketones in TFAA/TfOH system is described. When the β-phenylpropionic acids were used as starting materials, they initially gave 1-indanones and then underwent further acylation with the formation of 2-(β-phenylpropionyl)-1-indanones as the main reaction products. In addition, the application of the proposed protocol allowed for the synthesis of selected polysubstituted pyrazoles in a one-pot procedure directly from acids and ketones.

An efficient synthesis of highly substituted indanones and chalcones promoted by superacid

A superacid promoted one-pot method was developed for the efficient synthesis of indanones. This process enabled the formation of a dual C–C bond between the aryl isopropyl ketones and benzaldehydes. Interestingly, when the reaction was performed between acetophenones and benzaldehydes, it was impeded after the aldol condensation and resulted in the corresponding chalcones.

A new intermediate in spontaneous styrene polymerisation inhibited by 2-nitrophenol

Spontaneous polymerisation of styrene inhibited by 2-nitrophenol leads to the formation of the unexpected benzoxazine.