Intramolecular Friedel-Crafts Reaction Research Articles

Intramolecular Friedel-Crafts Reaction with Trifluoroacetic Acid: Synthesizing Some New Functionalized 9-Aryl/Alkyl Thioxanthenes.

In this study, a series of halogen-substituted thioxanthenes were synthesized because the most important and biologically active derivatives of xanthenes are thioxanthenes. In order to obtain new thioxanthene derivatives, first, the starting molecules were synthesized by the appropriate reaction methods in two steps. The intramolecular Friedel-Crafts alkylation (FCA) method was used to convert the prepared three aromatic substituted starting alcohol compounds to their corresponding thioxanthenes by cyclization. For the intramolecular FCA reaction of secondary alcohols, which are the starting compounds (1a-1t), organic Bro̷nsted acids, which require more innovative, easier, and suitable reaction conditions, were used instead of halide reagents with corrosive effects as classical FCA catalysts. Trifluoroacetic acid was determined to be the organocatalyst with the best yield. Therefore, some original 9-aryl/alkyl thioxanthene derivatives (2a-2t) were synthesized using the optimized FCA method. In addition, a new sulfone derivative of thioxanthene 3i was prepared by performing the oxidation reaction with one of the obtained new thioxanthene 2i. Thioxanthenes and their derivatives are important heterocyclic structures that contain pharmacologically valuable sulfur and are used in the treatment of psychotic diseases such as Alzheimer's or schizophrenia, as well as a number of potent biological activities.

Accessing Medium-Sized Rings via Vinyl Carbocation Intermediates.

Medium-sized rings (8-11-membered cycles) are often more challenging to synthesize than smaller rings (5-7-membered cycles) due to ring strain. Herein, we report a catalytic method for forming 8- and 9-membered rings that proceeds via the intramolecular Friedel-Crafts reactions of vinyl carbocation intermediates. These reactive species are generated catalytically through the ionization of vinyl toluenesulfonates by a Lewis acidic lithium cation-weakly coordinating anion salt.

Route to Functionalized Tetrahydrobenzo[d]azepines via Re2O7-Mediated Intramolecular Friedel-Crafts Reaction.

We describe a Re2O7-mediated intramolecular dehydrative Friedel-Crafts reaction for the efficient synthesis of various benzo-fused heterocycles such as benzazepines and benzazocines. This process is characterized by a broad substrate scope, mild reaction conditions, high efficiency, and high atom economy. The potential application of this methodology was exemplified by the facile preparation of a NMDA antagonist as well as a key intermediate en route to SKF 38393.

Direct synthesis of phenanthrenyl triflates from 1-biphenylyl-2-diazo-2-aryl ketones and triflic anhydride.

A strategy for direct synthesis of phenanthrenyl triflates from 1-biphenylyl-2-diazo-2-aryl ketones and triflic anhydride is described. The reaction of 1-biphenylyl-2-diazo-2-aryl ketones with triflic anhydride proceeded smoothly in the presence of 2,6-di-tert-butylpyridine under mild conditions to produce phenanthrenyl triflates in high to excellent yields. The phenanthrenyl triflate products were demonstrated to be utilized as coupling partners in various coupling reactions. The proposed mechanism involves an intramolecular Friedel-Crafts reaction of a vinyl cation intermediate formed in situ.

Scandium-Catalyzed Phenol-Directed Construction of 5-Carbonyl-4-hydroxybenzofurans via Intramolecular Friedel-Crafts Reaction.

Herein we report a scandium-catalyzed regioselective synthesis of 5-carbonyl-4-hydroxybenzofurans via a phenol-directed intramolecular Friedel-Crafts reaction. This synthetic method was applied for the total synthesis of furanoflavones. Experimental studies and density functional theory calculations suggest that hydrogen bond interactions between the phenolic hydroxy group and the scandium complex realize regioselective intramolecular cyclization.

From Formyl-Corroles to Non-Aromatic Porphyrinoids

In 1998, it would have been impossible to imagine that only 20 years later the chemistry of one of corroles would expand to create an independent field of study. The synthesis of corroles has undergone incredible changes. From multistep strategies that attracted only practitioners in the field, the procedure has been transformed into a one-pot process from commercially available reagents. The synthesis of meso-substituted corroles evolved quickly during the first seven years after Paolesse’s and Gross’s discovery [1,2]. The methodology which led to trans-A2B-corroles (i.e., corroles bearing substituents A at positions 5 and 15 and substituent B at position 10) from dipyrranes and aldehydes was discovered in 2000 and optimized several times prior to 2006, when we discovered that as long as aldehydes and dipyrranes were relatively small and/or hydrophilic, performing this reaction in a mixture of water and methanol in the presence of HCl allowed the yields to increase from 6-30% to ~55% [3,4]. The synthetic revolution made it possible to try risky ideas in diverse areas of materials chemistry and in various biology- and medicine-oriented applications. Multiple challenges still remain in the preparation of corroles.One of those challenges is the preparation of corroles possessing CHO groups. Free formyl groups can be reacted with multiple nucleophiles forming more complex and more advanced structures. At the same time CHO is the reacting group pivotal in the corrole synthesis. Attempting to solve this conundrum we recently developed the synthesis of tris(4-formylphenyl)corrole in straightforward fashion. During the realization of this project we discovered that 10-(2-formylphenyl)corrole undergoes intramolecular Friedel-Crafts reaction leading to non-aromatic, π-expanded corrole. This divalent macrocycle possess intriguing photophysical properties and has an ability to form complexes with various metals.References Gross, Z.; Galili, N.; Saltsman, I. Angew. Chem. Int. Ed. 1999, 38, 1427−1429.Paolesse, R.; Jaquinod, L.; Nurco, D. J.; Mini, S.; Sagone, F.; Boschi, T.; Smith, K. M. Chem. Commun. 1999, 1307−1308.Koszarna, B.; Gryko, D. T. J. Org. Chem. 2006, 71, 3707−3717.Orłowski, R.; Gryko, D.; Gryko, D. T. Chem. Rev. 2017, 117, 3102-3137. Figure 1

A new class of potent liver injury protective compounds: Structural elucidation, total synthesis and bioactivity study.

A new class of potent liver injury protective compounds, phychetins A-D (1-4) featuring an unique 6/6/5/6/5 pentacyclic framework, were isolated and structurally characterized from a Chinese medicinal plant Phyllanthus franchetianus. Compounds 2-4 are three pairs of enantiomers that were initially obtained in a racemic manner, and were further separated by chiral HPLC preparation. Compounds 1-4 were proposed to be originated biosynthetically from a coexisting lignan via an intramolecular Friedel-Crafts reaction as the key step. A bioinspired total synthesis strategy was thus designated, and allowed the effective syntheses of compounds 2-4 in high yields. Some of compounds exhibited significant anti-inflammatory activities invitro via suppressing the production of pro-inflammatory cytokine IL-1β. Notably, compound 4, the most active enantiomeric pair invitro, displayed prominent potent protecting activity against liver injury at a low dose of 3mg/kg in mice, which could serve as a promising lead for the development of acute liver injury therapeutic agent.

Eco-friendly, green and new metal-free intramolecular Friedel–Crafts reaction to synthesis of Acridones derivatives using phenylboronic acid derivatives

Herein, we report a new, facile, versatile metal-free method for preparation of the various Acridones through an intramolecular carbonylation of 2-(phenylamino)benzoic acid derivatives and phenylboronic acid derivatives as activating agent for activation of carboxylic acid group in intramolecular CC bond formation through Friedel–Crafts reaction. The reaction proceeds under solvent-free conditions, tolerates a wide range of functional groups, and provides rapid access to a range of the Acridones in good to excellent yields.

Facile preparation of polycyclic halogen-substituted 1,2,3-triazoles by using intramolecular Huisgen cycloaddition.

When 1-(ω-azidoalkyl)-2-(2,2-dihalovinyl)arenes were heated in DMF, the intramolecular Huisgen cycloaddition of an azido group with a 1,1-dihalovinyl group afforded 5-halo-1,2,3-triazole-fused tricyclic benzo compounds. Based on the remaining bromo groups, carbon elongation by the Mizoroki-Heck or Suzuki-Miyaura coupling reactions, followed by an intramolecular Friedel-Crafts reaction, afforded polycyclic compounds with fused triazole rings. Thereafter, the bromo groups were converted into 2-nitrophenyl groups via the Suzuki-Miyaura coupling reaction, which was followed by the Cadogan reaction; a fluorescent pentacyclic compound was obtained.

Superacid Promoted Synthesis of 9,9'-Spirobifluorenes and Related Aza- and Diazaspirocycles.

A variety of 9,9'-spirobifluorenes and related azaspirocycles and diazaspirocycles have been prepared in high yields by intramolecular Friedel-Crafts reaction using the Brønsted superacid, triflic acid (CF3SO3H). Compared to weaker Brønsted acids, the superacid consistently provides better yields along with reduced reaction times and it eliminates the need for heating. The superacid is particularly effective when dicationic electrophilic intermediates are generated in the conversions, for example with the diazaspirocycle syntheses.

Access to Hexahydroindeno[2,1-c]pyran-Based Propellanes by a Domino Prins/Friedel–Crafts Cyclization

AbstractStarting from readily available cyclic homoallylic alcohols, a Prins reaction allowed the formation of a bicyclic tetrahydropyranyl carbocation intermediate that is only trapped by electron-rich aromatic rings according a further intramolecular Friedel–Crafts reaction leading to new [4.4.3]propellane structures.

Discovery, total syntheses and potent anti-inflammatory activity of pyrrolinone-fused benzoazepine alkaloids Asperazepanones A and B from Aspergillus candidus

Natural products are well established as an important resource and play an important role in drug discovery. Here, two pyrrolinone-fused benzoazepine alkaloids, (+)-asperazepanones A (1) and B (2) with a 6/7/5 ring system, together with the artifact (−)-asperazepanone A (1), were isolated from the coral-derived Aspergillus candidus fungus. Their structures including absolute configurations were elucidated by extensive spectroscopic methods, single crystal X-ray diffraction, and ECD calculations. Furthermore, total syntheses of (±)-1 and (±)-2 have been achieved starting from the commercially L-aspartic acid diethyl ester hydrochloride and monoethyl malonate in 7 and 8 steps, respectively. The key step in the syntheses was an intramolecular Friedel-Crafts reaction to build the unique tricyclic skeleton. Interestingly, (+)-2 not only showed obviously inhibitory activity against NO production, but also inhibited potent LPS-induced expression of TNF-α and IL-6 at the concentration of 0.1 μM. It thus represents a potentially promising lead for anti-inflammatory drug discovery.

Bischler–Napieralski Synthesis of Polycyclic N-Heteroaromatics Based on Tf2O-Promoted Electrophilic Activation of N-Aryl-2-Propynamides

2-Propynamides have been never used as substrates in classic and Tf2O-promoted Bischler-Napieralski reactions. In this article, a novel tandem synthesis of benzo[a]acridines is developed from N-aryl-2-propynamides and alkynes consisting of a Tf2O-promoted intermolecular Bischler-Napieralski reaction and a TfOH-promoted intramolecular Friedel-Crafts reaction.

A Concise Total Synthesis of the Fungal Isoquinoline Alkaloid TMC-120B

Recent reports of antiepileptic activity of the fungal alkaloid TMC-120B have renewed the interest in this natural product. Previous total syntheses of TMC-120B comprise many steps and have low overall yields (11–17 steps, 1.5–2.9% yield). Thus, to access this compound more efficiently, we herein present a concise and significantly improved total synthesis of the natural product. Our short synthesis relies on two key cyclization steps to assemble the central scaffold: isoquinoline formation via an ethynyl-imino cyclization and an intramolecular Friedel-Crafts reaction to form the furanone.

Synthesis of Indolyl-Tethered Spiro[cyclobutane-1,1'-indenes] through Cascade Reactions of 1-(Pyridin-2-yl)-1H-indoles with Alkynyl Cyclobutanols.

Presented herein is an efficient and unprecedented synthesis of indolyl-tethered spiro[cyclobutane-1,1'-indenes] through the cascade reaction of 1-(pyridin-2-yl)-1H-indoles with alkynyl cyclobutanols. Mechanistic experiments implicate a sequential process in which 1-(pyridin-2-yl)-1H-indole first undergoes an alkenylation with alkynyl cyclobutanol followed by an intramolecular Friedel-Crafts reaction to give the title products. The utility of this novel protocol was reflected by the ample substrate scope, high chemo- and regioselectivity, removable directing group, and scalable preparation. In addition, the product thus obtained can be further derivatized quite efficiently.

Stereospecific synthesis of aryltetraline lignan analogues using 1,6-bis(dipropylboryl)hexa-2,4-diene

A novel convenient two-stage synthesis of aryltetraline lignin analogues from aromatic aldehydes and diallyl diboron derivatives on the basis of intramolecular Friedel–Crafts reaction has been developed.

Transition-metal-free intramolecular Friedel-Crafts reaction by alkene activation: A method for the synthesis of some novel xanthene derivatives.

In this work, new derivatives (substituted 9-methyl-9-arylxanthenes) of xanthene compounds (5a–l) of possible biological significance were synthesized by developing a new synthesis method. In order to obtain xanthene derivatives, the original alkene compounds to be used as the starting materials were synthesized in four steps using appropriate reactions. A cyclization reaction by intramolecular Friedel–Crafts alkylation was carried out in order to synthesize the desired xanthene derivatives using the alkenes as starting compounds. The intramolecular Friedel–Crafts reaction was catalyzed by trifluoroacetic acid (TFA) and provided some novel substituted 9-methyl-9-arylxanthenes with good yields at room temperature within 6–24 hours. As a result, an alkene compound was used for activation with TFA in the synthesis of xanthene through intramolecular Friedel–Crafts alkylation for the first time.

Collective Asymmetric Total Synthesis of C-11 Oxygenated Cephalotaxus Alkaloids.

While numerous studies pertaining to the total synthesis of Cephalotaxus alkaloids have been reported, only two strategies have been reported to date for the successful synthesis of the C-11 oxygenated subset, due to the additional synthetic challenge posed by the remote C-11 stereocenter. Herein, we report the collective asymmetric total synthesis of C-11 oxygenated Cephalotaxus alkaloids using a chiral proline both as a starting material and as the only chirality source. A tetracyclic advanced intermediate was synthesized in a highly stereoselective manner from l-proline in 8 steps involving sequential chirality transfer steps such as a diastereoselective N-alkylation, stereospecific Stevens rearrangement and intramolecular Friedel-Crafts reaction via an unusual O-acyloxocarbenium intermediate. From a common intermediate, the asymmetric total synthesis of six C-11 oxygenated Cephalotaxus alkaloids was completed by a series of oxidation state adjustments.

Collective Asymmetric Total Synthesis of C‐11 Oxygenated Cephalotaxus Alkaloids

AbstractWhile numerous studies pertaining to the total synthesis of Cephalotaxus alkaloids have been reported, only two strategies have been reported to date for the successful synthesis of the C‐11 oxygenated subset, due to the additional synthetic challenge posed by the remote C‐11 stereocenter. Herein, we report the collective asymmetric total synthesis of C‐11 oxygenated Cephalotaxus alkaloids using a chiral proline both as a starting material and as the only chirality source. A tetracyclic advanced intermediate was synthesized in a highly stereoselective manner from l‐proline in 8 steps involving sequential chirality transfer steps such as a diastereoselective N‐alkylation, stereospecific Stevens rearrangement and intramolecular Friedel–Crafts reaction via an unusual O‐acyloxocarbenium intermediate. From a common intermediate, the asymmetric total synthesis of six C‐11 oxygenated Cephalotaxus alkaloids was completed by a series of oxidation state adjustments.

Stereocontrolled syntheses of (-)- and (+)-γ-diisoeugenol along with optically active eight stereoisomers of 7,8'-epoxy-8,7'-neolignan.

It was shown that reduction of the tertiary benzylic hydroxy group of (2R,3S,4R,5S)-3,5-bis(4-benzyloxy-3-methoxyphenyl)-2,4-dimethyltetrahydro-3-furanol 17 followed by the intramolecular Friedel-Crafts reaction gave exclusively indane with (7S,7'S,8R,8'R)-2,7'-cyclo-7,8'-neolignan structure 18 along with (7S,7'R,8S,8'R)-7,8'-epoxy-8,7'-neolignan structure 19. Indane 18 was converted to (-)-γ-diisoeugenol ((-)-4). On the other hand, (2S,3R,4R,5S)-3,5-bis(4-benzyloxy-3-methoxyphenyl)-2,4-dimethyltetrahydro-3-furanol 22 did not afford indane, but the tetrahydrofuran structure with (7S,7'S,8S,8'S)-7,8'-epoxy-8,7'-neolignan structure 23 and 7'-epi-23.