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Since the pioneer reports of the groups of Akiyama and Terada on Brønsted acid organocatalysis, this field never stopped growing with the development of ingenious strategies for the activation of challenging poorly reactive substrates. The development of superacidic organocatalysts is an important way to selectively functionalize reluctant electrophiles and other approaches have also emerged such as the combination of Lewis and Brønsted acids as well as the consecutive organocatalysis and superacid activation. This Concept aims to highlight these different strategies and demonstrate their complementarity. [ABSTRACT FROM AUTHOR]

The field of medicinal chemistry is currently witnessing a deuterium rush owing to the remarkable properties of this element as bioisoster of hydrogen atom. Aromatic hydrogen isotope exchange (HIE) is one of the most studied strategies nowadays as it promises to access deuterium‐modified drugs directly from their non‐labeled parents. While most of the recent studies focus on metal‐catalyzed C−H activation strategy, the use of superacidic conditions has been largely overlooked. This study shows that the use of TfOD as reaction medium allows the late‐stage polydeuteration of a broad library of pharmaceuticals bearing a wide array of functional groups, complementing existing procedures. [ABSTRACT FROM AUTHOR]

Site‐selective functionalization of arenes that is complementary to classical aromatic substitution reactions remains a long‐standing quest in organic synthesis. Exploiting the generation of halenium ion through oxidative process and the protonation of the nitrogen containing function in HF/SbF5, the chlorination and iodination of classically inert Csp2−H bonds of aromatic amines occurs. Furthermore, the superacid‐promoted (poly)protonation of the molecules acts as a protection, favoring the late‐stage selective halogenation of natural alkaloids and active pharmaceutical ingredients [ABSTRACT FROM AUTHOR]

Abstract: A series of new, halogen containing N-substituted 4-aminobenzenesulfonamides were synthesized by using superacid HF/SbF5 chemistry and investigated as inhibitors of several human carbonic anhydrase (hCA, EC 4.2.1.1) isoforms, that is, the cytosolic hCA I and II and, the tumor-associated transmembrane isoforms hCA IX and XII. Despite the substitution of the sulfonamide function, the presence of fluorine atom(s) in β position of the sulfonamide function strongly favors hCA inhibition. A similar effect of the β-fluorinated alkyl substitution on the amino function has been also observed. Among the tested compounds, several chlorinated derivatives have been identified as selective nanomolar, tumor-associated isoforms inhibitors. These non-primary sulfonamides probably bind in the coumarin-binding site, at the entrance of the cavity, and not to the metal ion as the primary sulfonamide inhibitors. [Copyright &y& Elsevier]

A series of benzofused sultams and fluorinated benzenesulfonamides were synthesized in superacid HF/SbF5 from simple N-allylic derivatives. Almost all of these original compounds showed micromolar inhibitory activities against carbonic anhydrases I and II. The fluorinated derivatives inhibit better the tumor-associated isoforms IX and XII, and one of the tested compounds showed inhibition in the nanomolar range. [ABSTRACT FROM AUTHOR]

Abstract: The reactivity of aliphatic amides/ketones/imines and nitriles was studied in superacid HF/SbF5 in the presence of CCl4. After the identification of the reaction intermediates by in situ NMR experiments, we propose that the sp3C–H bond functionalization (fluorination) by the superacid system is strongly dependant on the superelectrophilic character of the distonic dicationic intermediates. [Copyright &y& Elsevier]

The novel cyclization/fluorination reaction of N-dienes in superacid was extended to substituted substrates. The influence of the substitution on superelectrophilic character of dicationic intermediates was shown and its dramatic effect on the synthesis of fluoropiperidinea was studied. On the basis of new dicationic α-chloronium ammonium intermediates, starting from halogen-substituted dienes, high-valued fluorinated piperidines were synthesized. [ABSTRACT FROM AUTHOR]

Abstract: In the superacidic media HF/SbF5, hydroxylation of several Tröger’s bases was performed using sodium persulfate as a hydroperoxonium H3 precursor. The obtained products are selectively hydroxylated in good yields on unusual positions of the aromatic rings. [Copyright &y& Elsevier]

Abstract: Nucleophilic para-fluorination of substituted anilines to afford 4-fluorocyclohexadieneimine derivatives is achieved in the presence of hypervalent iodine and pyridinium polyhydrogen fluoride. [Copyright &y& Elsevier]

Diacetoxyiodobenzene (PIDA) and bis(trifluoroacetoxy)iodobenzene (PIFA) in the presence of pyridinium polyhydrogen fluoride (PPHF) are effective for the fluorination of para-substituted phenols to give a variety of 4-fluorocyclohexa-2,5-dienones in a good yield. (R,S)-1,1′-Bi-5,6,7,8-tetrahydro-2-naphthol (and its monoacetate) yields atropoisomeric fluorocyclohexadienones. The 4-substituted carbamate open-chain phenols were readily converted to fluorohydroindolenone and fluorohydroquinolenone derivatives by intramolecular conjugate addition. [Copyright &y& Elsevier]

Reaction of cyclic ketones 2–6 and imines 15–17 in HF/SbF5 in presence of CCl4 yield hydroxy or fluoroderivatives, hydride abstraction occurring at a site located far from the functional group. Whereas ketones 2–5 yield only hydroxy derivatives, through cyclic carboxonium ion, imines 15, 16 N-protonated in the media conditions give only fluoroderivatives 18, 19, respectively, after quenching with HF–pyridine. Ring contraction is operative when starting from large membered ring ketones 24 and 25, and imine 26, leading to a mixture of hydroxy or fluoro cyclohexanones and/or cycloheptanones. [Copyright &y& Elsevier]

Under superacid conditions, aromatic amines are directly and regioselectively 1,1‐difluoroethylated. Low temperature in situ NMR studies confirmed the presence of benzylic α‐fluoronium and α‐chloronium ions as key intermediates in the reaction. This method has a wide substrate scope and can be applied to the late‐stage functionalization of natural alkaloids and active pharmaceutical ingredients. [ABSTRACT FROM AUTHOR]

The insertion of fluorine atoms and/or fluoroalkyl groups can lead to many beneficial effects in biologically active molecules, such as enhanced metabolic stability, bioavailability, lipophilicity, and membrane permeability, as well as a strengthening of protein–ligand binding interactions. However, this "magic effect" of fluorine atom(s) insertion can often be meaningless. Taking advantage of the wide range of data coming from the quest for carbonic anhydrase (CA) fluorinated inhibitors, this Minireview attempts to give "general guidelines" on how to wisely insert fluorine atom(s) within an inhibitor moiety to precisely enhance or disrupt ligand–protein interactions, depending on the target location of the fluorine substitution in the ligand. Multiple approaches such as ITC, kinetic and inhibition studies, X‐ray crystallography, and NMR spectroscopy are useful in dissecting single binding contributions to the overall observed effect. The exploitation of innovative directions made in the field of protein and ligand‐based fluorine NMR screening is also discussed to avoid misconduct and finely tune the exploitation of selective fluorine atom insertion in the future. [ABSTRACT FROM AUTHOR]

The insertion of fluorine atoms and/or fluoroalkyl groups can lead to many beneficial effects in biologically active molecules, such as enhanced metabolic stability, bioavailability, lipophilicity, and membrane permeability, as well as a strengthening of protein–ligand binding interactions. However, this "magic effect" of fluorine atom(s) insertion can often be meaningless. Taking advantage of the wide range of data coming from the quest for carbonic anhydrase (CA) fluorinated inhibitors, this Minireview attempts to give "general guidelines" on how to wisely insert fluorine atom(s) within an inhibitor moiety to precisely enhance or disrupt ligand–protein interactions, depending on the target location of the fluorine substitution in the ligand. Multiple approaches such as ITC, kinetic and inhibition studies, X‐ray crystallography, and NMR spectroscopy are useful in dissecting single binding contributions to the overall observed effect. The exploitation of innovative directions made in the field of protein and ligand‐based fluorine NMR screening is also discussed to avoid misconduct and finely tune the exploitation of selective fluorine atom insertion in the future. [ABSTRACT FROM AUTHOR]

Here we report a method to reorganize the core structure of aliphatic unsaturated nitrogen‐containing substrates exploiting polyprotonation in superacid solutions. The superelectrophilic activation of N‐isopropyl systems allows for the selective formal Csp3−H activation/cyclization or homologation / functionalization of nitrogen‐containing substrates. This study also reveals that this skeletal reorganization can be controlled through protonation interplay. The mechanism of this process involves an original sequence of C−N bond cleavage, isopropyl cation generation and subsequent C−N bond and C−C bond formation. This was demonstrated through in situ NMR analysis and labelling experiments, also confirmed by DFT calculations. [ABSTRACT FROM AUTHOR]

Here we report a method to reorganize the core structure of aliphatic unsaturated nitrogen‐containing substrates exploiting polyprotonation in superacid solutions. The superelectrophilic activation of N‐isopropyl systems allows for the selective formal Csp3−H activation/cyclization or homologation / functionalization of nitrogen‐containing substrates. This study also reveals that this skeletal reorganization can be controlled through protonation interplay. The mechanism of this process involves an original sequence of C−N bond cleavage, isopropyl cation generation and subsequent C−N bond and C−C bond formation. This was demonstrated through in situ NMR analysis and labelling experiments, also confirmed by DFT calculations. [ABSTRACT FROM AUTHOR]

Enantioenriched complex fused‐tricyclic azepanes or bridged‐polycyclic azocanes were constructed via a two‐step sequence involving an enantioselective organocascade followed by superacid activation of the domino adduct. The activated oxa‐bridged azepane acts as a key hidden heptacyclic chiral N‐acyl iminium ion triggering a chemo‐ and diastereoselective intramolecular mono‐ or di‐arylation. [ABSTRACT FROM AUTHOR]

The selective synthesis of tetrahydroquinolines and fluorinated arylamines was performed in superacid HF/SbF5 through a superelectrophilic ammonium-carbenium activation process. This anti-Markovnikov oriented reaction was applied to the straightforward synthesis of highly valued (fluorinated) nitrogen-containing heterocyclic compounds. [ABSTRACT FROM AUTHOR]

The transformation of glycals into 2,3‐unsaturated glycosyl derivatives, reported by Ferrier in 1962, is supposed to involve an α,β unsaturated glycosyl cation, an elusive ionic species that has still to be observed experimentally. Herein, while combination of TfOH and flow conditions failed to observe this ionic species, its extended lifetime in superacid solutions allowed its characterization by NMR‐based structural analysis supported by DFT calculations. This allyloxycarbenium ion was further exploited in the Ferrier rearrangement to afford unsaturated nitrogen‐containing C‐aryl glycosides and C‐alkyl glycosides under superacid and flow conditions, respectively. [ABSTRACT FROM AUTHOR]

The transformation of glycals into 2,3‐unsaturated glycosyl derivatives, reported by Ferrier in 1962, is supposed to involve an α,β unsaturated glycosyl cation, an elusive ionic species that has still to be observed experimentally. Herein, while combination of TfOH and flow conditions failed to observe this ionic species, its extended lifetime in superacid solutions allowed its characterization by NMR‐based structural analysis supported by DFT calculations. This allyloxycarbenium ion was further exploited in the Ferrier rearrangement to afford unsaturated nitrogen‐containing C‐aryl glycosides and C‐alkyl glycosides under superacid and flow conditions, respectively. [ABSTRACT FROM AUTHOR]

In superacid, quinine rearranges to yield a novel oxazapolycyclic compound. [Copyright &y& Elsevier]

Achieving in a straightforward way the synthesis of enantioenriched elaborated three‐dimensional molecules related to bioactive natural products remains a long‐standing quest in organic synthesis. Enantioselective organocatalysis potentially offers a unique opportunity to solve this problem, especially when combined with complementary modes of activation. Here, we report the sequential association of organocatalytic and superacid activations of simple linear achiral readily available precursors to promote the formation of unique highly elaborated chiral methylene‐bridged benzazocanes exhibiting three to five fully‐controlled stereocenters. This peculiar backbone, difficult to assemble by standard synthetic approaches, is closely related to bioactive natural and synthetic morphinans and benzomorphans. The formation of a highly reactive chiral 7‐membered ring N‐acyl iminium superelectrophilic ion, evidenced by low‐temperature in situ NMR experiments, triggers a challenging stereoselective Friedel–Crafts‐type cyclization. [ABSTRACT FROM AUTHOR]

Achieving in a straightforward way the synthesis of enantioenriched elaborated three‐dimensional molecules related to bioactive natural products remains a long‐standing quest in organic synthesis. Enantioselective organocatalysis potentially offers a unique opportunity to solve this problem, especially when combined with complementary modes of activation. Here, we report the sequential association of organocatalytic and superacid activations of simple linear achiral readily available precursors to promote the formation of unique highly elaborated chiral methylene‐bridged benzazocanes exhibiting three to five fully‐controlled stereocenters. This peculiar backbone, difficult to assemble by standard synthetic approaches, is closely related to bioactive natural and synthetic morphinans and benzomorphans. The formation of a highly reactive chiral 7‐membered ring N‐acyl iminium superelectrophilic ion, evidenced by low‐temperature in situ NMR experiments, triggers a challenging stereoselective Friedel–Crafts‐type cyclization. [ABSTRACT FROM AUTHOR]

Exploiting trimethylsilyltrifluoromethanesulfonate as Lewis acid, (hetero)aromatics underwent regioselective and direct carbamoylation. The method is based on the in situ generation of a highly electrophilic carbamoyl triflate active species. TMSOTf acts as Lewis acid to activate carbamoyl chlorides and generates highly electrophilic carbamoyl triflates in situ; these are active species for late‐stage aromatic carbamoylation. [ABSTRACT FROM AUTHOR]

Upon activation under superacid conditions, functionalized tailor-made N-SCF3 sulfenamides served as reagents for the trifluoromethylthiolation of aromatic amines. This method has a broad substrate scope and can be used for the late-stage functionalization of complex molecules such as alkaloids or steroids. Mechanistic studies based on in situ low-temperature NMR spectroscopy revealed the involvement of dicationic superelectrophilic intermediates. [ABSTRACT FROM AUTHOR]

Upon activation under superacid conditions, functionalized tailor-made N-SCF3 sulfenamides served as reagents for the trifluoromethylthiolation of aromatic amines. This method has a broad substrate scope and can be used for the late-stage functionalization of complex molecules such as alkaloids or steroids. Mechanistic studies based on in situ low-temperature NMR spectroscopy revealed the involvement of dicationic superelectrophilic intermediates. [ABSTRACT FROM AUTHOR]

An efficient and straightforward regio-controlled route to β-fluoro-γ-chlorinated amines was developed via an ammonium–chloronium superelectrophilic activation in superacid HF/SbF 5 . Through halogen directing effect the method was extended to a variety of (poly)halofluorinated building blocks amenable for further synthetic modifications. The direct synthesis of chlorofluorinated analogues of bioactive compounds via this process confirmed the ability to use this strategy for further applications in medicinal chemistry. [ABSTRACT FROM AUTHOR]

(E)- and (Z)-α-fluoroenamides could be easily prepared with high levels of chemo- and regioselectivities by hydrofluorination of readily available ynamides with HF/pyridine. The scope and limitations of this new process for the hydrofluorination of ynamides, as well as the stability of the resulting α-fluoroenamides, have been extensively studied. Theoretical calculations at the MP2 and B3LYP levels of theory showed that the resulting fluoroenamides exhibit geometrical and electronic properties that partially mirror those of ureas, therefore demonstrating that the hydrofluorination of ynamides provides a general, straightforward, and user-friendly approach to bioisosteres of ureas, potent building blocks for biological studies and medicinal chemistry. [ABSTRACT FROM AUTHOR]

A novel and efficient keteniminium-initiated cationic polycyclization is reported. This reaction, which only requires triflic acid or bistriflimide as promoters, affords a straightforward entry to polycyclic nitrogen heterocycles possessing up to three contiguous stereocenters and seven fused cycles. These complex, polycyclic molecules can be obtained in a single operation from readily available ynamides which were shown to be remarkable building blocks for multiple, consecutive cationic transformations. [ABSTRACT FROM AUTHOR]

Abstract: In HF/SbF5, in the presence of CCl4 or NBS, unsaturated or hydroxylated piperidines yield difluoroanalogues in good yields. The ability to perform hydride abstraction on chloroderivatives, and the ability to form bridged bromonium ions from unsaturated substrates seem to completely influence the reaction course. Some aspects of the mechanism were clarified by DFT calculations. [Copyright &y& Elsevier]

Abstract: In HF-SbF5, quinine 1a or its dihydrochloride rearranges into compound 3 (89%), the preferred conformation of the substrate favouring the observed cyclization. Under similar conditions epiquinine 2a dihydrochloride yields in equal amounts two 10,10-difluoro derivatives, epimeric at C-3. In this case, the more stable conformation of the substrate in which the benzylic hydroxyl group is ‘exo’ to the quinuclidyl moiety, prevents the cyclisation. Similarly acetates 1b and 2b give the corresponding 10,10-difluoro derivatives epimeric at C-3. Formation of gem-difluoro compounds implies the formation of chloro intermediates at C-10 followed by an hydride abstraction, yielding an α-chloronium ion. This one is trapped by a fluoride ion and leads to the product by halogen exchange. [Copyright &y& Elsevier]

Superacid activation of N‐SCF3 sulfenamide reagents generates diprotonated superelectrophilic species for the trifluoromethylthiolation of aromatic amines, as shown by T. Billard, S. Thibaudeau, and co‐workers in their Communication on page 173 ff. This method can be used for the late‐stage functionalization of complex biomolecules such as alkaloids and steroids. [ABSTRACT FROM AUTHOR]