Intramolecular Acylation Research Articles

Regioselection in the synthesis of 4-benzyltetral-1-ones and the new 4-arylbenzosuber-1-ones

The intramolecular Friedel-Crafts acylation of 4,5-diarylpentanoic acids has the possibility to cyclise to either a 6-membered ring to give 4-benzyltetral-1-one or a 7-membered ring to give 4-arylbenzosuber-1-one. Of these, only the former compound class has previously been reported. The impact of the substituents positioning on the outcome of the cyclisation has been investigated. The complete formation of either the tetralone or the benzosuberone regioisomer was possible under the same reaction conditions, dependent upon the ring activation and/or deactivation of the chosen substituents. Selected bromo or methoxy substituents could be used as auxiliaries, included in precursors to afford the desired regioisomer and then subsequently removed. • First examples of 4-arylbenzosuber-1-ones. • Regioselection for 4-arylbenzosuber-1-ones or 4-benzyltetral-1-ones driven by substituents. • Selected substituents can act as regioselection auxiliaries by removal or modification.

Catalytic, Regioselective Hydrocarbofunctionalization of Unactivated Alkenes Triggered by trans-Acetoxypalladation of Alkynes.

Herein we demonstrate a Pd(II)-catalyzed regioselective hydrocarbofunctionalization of unactivated alkenes. The σ-vinyl-palladium(II) intermediate generated by the trans-acetoxypalladation of alkynes was added across carbon-carbon double bond to realize an efficient hydroalkenylation protocol. Bidentate auxiliary 8-aminoquinoline controls the regioselectivity of the carbopalladation step and thereby controls the regioselectivity of the hydroalkenylation. Additionally, when alkynes containing a hydroxy group at the three- or four-position were employed, the cascade sequence led to 1,6-dicarbonyl compounds via hydroalkenylation followed by intramolecular acyl migration.

Depsipeptide synthesis using a late-stage Ag(i)-promoted macrolactonisation of peptide thioamides.

Macrolactonisation of peptides to generate cyclic depsipeptides is often challenging due to the low nucleophilicity of hydroxyl groups, epimerisation, cyclodimerisation, and potential acyl transfer reactions of the ester. Herein, we report a novel macrolactonisation strategy employing a Ag(i)-promoted conversion of peptide thioamides to isoimide intermediates, which undergo site-selective intramolecular acyl transfer to serine/threonine side chains to generate the macrolactone.

Generation of Mixed Anhydrides via Oxidative Fragmentation of Tertiary Cyclopropanols with Phenyliodine(III) Dicarboxylates.

Oxidative fragmentation of tertiary cyclopropanols with phenyliodine(III) dicarboxylates in aprotic solvents (dichloromethane, chloroform, toluene) produces mixed anhydrides. The fragmentation reaction is especially facile with phenyliodine(III) reagents bearing electron-withdrawing carboxylate ligands (trifluoroacetyl, 2,4,6-trichlorobenzoyl, 3-nitrobenzoyl), and affords 95−98% yields of the corresponding mixed anhydride products. The latter can be straightforwardly applied for the acylation of various nitrogen, oxygen and sulfur-centered nucleophiles (primary and secondary amines, hydroxylamines, primary alcohols, phenols, thiols). Intramolecular acylation yielding macrocyclic lactones can also be performed. The developed transformation has bolstered the synthetic utility of cyclopropanols as pluripotent intermediates in diversity-oriented synthesis of bioactive natural products and their synthetic congeners. For example, it was successfully applied for the last-stage modification of a cyclic peptide to produce a precursor of a known histone deacetylase inhibitor.

Reaction of 5-phenylpenta-2,4-dienoic acid with benzene in trifluoromethanesulfonic acid

The reaction of 5-phenylpenta-2,4-dienoic acid with benzene in CF3SO3H, depending on the reaction conditions, gives three products, namely, 5,5-diphenylpent-2-enoic acid and tetralone and indanone derivatives. These carbocyclic compounds are formed through the addition of two benzene molecules to the starting diene acid and subsequent intramolecular acylation.

Total synthesis of agastaquinone, a diterpenoid quinone isolated from Agastache rugosa

Agastaquinone is a tricyclic diterpenoid isolated from Agastache rugose. The first total synthesis of agastaquinone was accomplished based on intramolecular Friedel-Crafts acylation of aryl lactone followed by aromatization leading to the tricyclic phenol core structure as a key step.

Direct Deoxygenative Intramolecular Acylation of Biarylcarboxylic Acids

A photocatalyzed intramolecular cyclization is developed for the synthesis of fluorenones. In this photoredox reaction, triphenylphosphine is used as an inexpensive and effective deoxygenative reagent for biarylcarboxylic acids to give acyl radicals, which quickly undergo intramolecular radical cyclization. Reactions in the presence of air and continuous flow photoredox technology demonstrate the generality and practicality of this process.

A structural chemistry practitioner: a fox rather than a hedgehog. Reversibility of Friedel–Crafts acyl rearrangements

A retrospective review of reversibility revealed in Friedel–Crafts acyl rearrangements of polycyclic aromatic ketones derived from the polycyclic aromatic hydrocarbons naphthalene, phenanthrene, anthracene, fluorene, pyrene, and fluoranthene is presented. The reactions were carried out in polyphosphoric acid (PPA). A distinction is made between completely reversible reaction (equilibrium reaction) denoted by ⇌ and reaction, both directions denoted by ⇆. Reaction, both direction is considered reversible reaction, not completely reversible reaction. Gore’s 1955 proposition that Friedel–Craft acylation of reactive hydrocarbons is a reversible process has been verified. Complete reversibility has been revealed in ortho ⇌ para acyl rearrangements of fluorofluorenones (1FFL ⇌ 3FFL) and in dibenzofluorenones (DBahFL ⇌ DBbhFL). Both cases are intramolecular acyl rearrangements. The majority of reversible intramolecular and intermolecular Friedel–Crafts acyl rearrangements are formally “reaction, both directions,” e.g., dibenzoylpyrenes 1,6-Bz2PY ⇆ 1,8-Bz2PY. Acyl rearrangements and reversibility in Friedel–Crafts acylations are associated with thermodynamic control. However, sometimes kinetic control wins out over thermodynamic control. Polycyclic aromatic ketones in which the carbonyl group is coplanar with the aromatic nucleus may undergo Friedel–Crafts acyl rearrangements. The reversibility concept has been applied to the synthesis of new and known linearly annelated polycyclic aromatic ketones by intramolecular Friedel–Crafts rearrangements of their angularly annelated constitutional isomers. A linkage between reversible Friedel–Crafts acyl rearrangements in PPA and the Scholl reaction has been established in benzoylnaphthalenes and in dibenzoylpyrenes. As a structural chemistry practitioner, the scientific personality of the first author belongs to the foxes, rather than to the hedgehogs.

Synthesis and Structure of Functionalized Zigzag Hydrocarbon Belts

AbstractDescribed in this paper are the synthesis and structure of novel and edge‐functionalized zigzag hydrocarbon belts. A stepwise “fjord‐stitching” strategy featuring repetitive intramolecular acylation reactions of a resorcin[4]arene derivative as the key steps afforded a biscarbonyl‐functionalized octahydrobelt[8]arene product. Facile ketone reduction with NaBH4 and nucleophilic addition with n‐butyllithium produced secondary and tertiary alcohol‐containing molecular belts, respectively. Selective oxidation reactions of biscarbonyl‐bearing octahydrobelt[8]arene with m‐CPBA and (PhSeO)2O furnished the corresponding lactone‐ and 1,4‐quinone‐embedded molecular belts. Depending on the functional groups on the edges, the acquired belt molecules adopt different shapes such as square prism, truncated cone, and elliptical cylinder.

Synthesis and Structure of Functionalized Zigzag Hydrocarbon Belts.

Described in this paper are the synthesis and structure of novel and edge-functionalized zigzag hydrocarbon belts. A stepwise "fjord-stitching" strategy featuring repetitive intramolecular acylation reactions of a resorcin[4]arene derivative as the key steps afforded a biscarbonyl-functionalized octahydrobelt[8]arene product. Facile ketone reduction with NaBH4 and nucleophilic addition with n-butyllithium produced secondary and tertiary alcohol-containing molecular belts, respectively. Selective oxidation reactions of biscarbonyl-bearing octahydrobelt[8]arene with m-CPBA and (PhSeO)2 O furnished the corresponding lactone- and 1,4-quinone-embedded molecular belts. Depending on the functional groups on the edges, the acquired belt molecules adopt different shapes such as square prism, truncated cone, and elliptical cylinder.

Fast and Stable N‐Terminal Cysteine Modification through Thiazolidino Boronate Mediated Acyl Transfer

AbstractWe report a novel conjugation of N‐terminal cysteines (NCys) that proceeds with fast kinetics and exquisite selectivity, thereby enabling facile modification of NCys‐bearing proteins in complex biological milieu. This new NCys conjugation proceeds via a thiazolidine boronate (TzB) intermediate that results from fast (k2: ≈5000 m−1 s−1) and reversible conjugation of NCys with 2‐formylphenylboronic acid (FPBA). We designed a FPBA derivative that upon TzB formation elicits intramolecular acyl transfer to give N‐acyl thiazolidines. In contrast to the quick hydrolysis of TzB, the N‐acylated thiazolidines exhibit robust stability under physiologic conditions. The utility of the TzB‐mediated NCys conjugation is demonstrated by rapid and non‐disruptive labeling of two enzymes. Furthermore, applying this chemistry to bacteriophage allows facile chemical modification of phage libraries, which greatly expands the chemical space amenable to phage display.

Bacterial lyso-form lipoproteins are synthesized via an intramolecular acyl chain migration

All bacterial lipoproteins share a variably acylated N-terminal cysteine residue. Gram-negative bacterial lipoproteins are triacylated with a thioether-linked diacylglycerol moiety and an N-acyl chain. The latter is transferred from a membrane phospholipid donor to the α-amino terminus by the enzyme lipoprotein N-acyltransferase (Lnt), using an active-site cysteine thioester covalent intermediate. Many Gram-positive Firmicutes also have N-acylated lipoproteins, but the enzymes catalyzing N-acylation remain uncharacterized. The integral membrane protein Lit (lipoprotein intramolecular transacylase) from the opportunistic nosocomial pathogen Enterococcus faecalis synthesizes a specific lysoform lipoprotein (N-acyl S-monoacylglycerol) chemotype by an unknown mechanism that helps this bacterium evade immune recognition by the Toll-like receptor 2 family complex. Here, we used a deuterium-labeled lipoprotein substrate with reconstituted Lit to investigate intramolecular acyl chain transfer. We observed that Lit transfers the sn-2 ester-linked lipid from the diacylglycerol moiety to the α-amino terminus without forming a covalent thioester intermediate. Utilizing Mut-Seq to analyze an alanine scan library of Lit alleles, we identified two stretches of functionally important amino acid residues containing two conserved histidines. Topology maps based on reporter fusion assays and cysteine accessibility placed both histidines in the extracellular half of the cytoplasmic membrane. We propose a general acid base-promoted catalytic mechanism, invoking direct nucleophilic attack by the substrate α-amino group on the sn-2 ester to form a cyclic tetrahedral intermediate that then collapses to produce lyso-lipoprotein. Lit is a unique example of an intramolecular transacylase differentiated from that catalyzed by Lnt, and provides insight into the heterogeneity of bacterial lipoprotein biosynthetic systems.

Synthesis of Naphthoxazinones in a One-Pot Two-Step Manner by the Application of Propylphosphonic Anhydride (T3P®)

A sequential one-pot two-step protocol has been elaborated for the synthesis of naphthoxazinones from 2-naphthol, methyl carbamate, and aromatic aldehydes. First, a three-component reaction was optimized with the dehydrating additive propylphosphonic anhydride (T3P®), resulting in 1-carbamatoalkyl 2-naphthols in good to excellent yields. Following the successful multicomponent approach, intramolecular acylation was performed at high temperature, again with the contribution of T3P®, resulting in naphthoxazinone derivatives in moderate yields. These two steps were optimized together in one-pot as well, and the sequential rise in the requisite temperature eventuated the optimal procedure for the multistep cascade.

Reactions of 3-arylpropenenitriles with arenes under superelectrophilic activation conditions: Hydroarylation of the carbon-carbon double bond followed by cyclization into 3-arylindanones

Reactions of 3-arylpropenenitriles [ArCHCHCN] with arenes [Ar’H] under the superelectrophilic activation conditions with Brønsted superacid TfOH (CF3SO3H) or strong Lewis acid AlBr3 result, first, in the formation of products of hydroarylation of the carbon-carbon double bond, 3,3-diarylpropanenitriles [Ar(Ar’)CHCH2CN]. Reactions may go further in TfOH leading to 3-arylindanones, as products of intramolecular aromatic acylation by the electrophilically activated nitrile group. Intermediate cationic species, derived at the protonation of the starting 3-arylpropenenitriles onto the carbon of CC bond and the nitrile nitrogen, have been studied by DFT calculation. A plausible reaction mechanism including the formation of highly reactive dications [(Ar)HC+–CH2C+ = NH] has been proposed. The obtained 3,3-diarylpropanenitriles have been transformed into pharmaceutically valuable 5-(2,2-diarylethyl)-1H-tetrazoles [Ar(Ar’)CHCH2Tetr] and 3-diarylpropylamines [Ar(Ar’)CH(CH2)2NH2] by the reactions with NaN3 and LiAlH4 correspondingly.

Selective Lysine Modification Enabled by Intramolecular Acyl Transfer.

The chemistries selectively modifying recombinant proteins are valuable for the discovery and development of biologic therapeutics. We report here a Lys modification strategy that engages a Cys residue to covalently tether the reagents to the target that facilitates a proximity-driven intramolecular O-to-N acyl-transfer process yielding desired Lys-acylated products. We utilized GLP-1 as a case study, followed by desulfurization of the Cys mutation to native Ala regenerating the native sequence in a traceless fashion.

The fate of acylated anthocyanins in mildly heated neutral solution

In neutral solution, anthocyanins acylated by hydroxycinnamic acids typically exhibit attractive blue colors and a higher resistance to color loss compared to their nonacylated homologs. However, they remain vulnerable to a poorly understood combination of oxidative and hydrolytic reactions that strongly contribute to color loss and limits their industrial applications. In this work, the thermal degradation of isolated red cabbage anthocyanins (0, 1 or 2 acyl groups) at pH 7 was investigated by UPLC-DAD-MS (low- and high-resolution). Non-oxidative alterations, including deacylation and intramolecular acyl transfer, were observed and found very dependent on the number and position of the acyl group(s) as well as on the presence of iron ions. At intermediate and advanced thermal degradation, several oxidative mechanisms were evidenced that lead to protocatechuic acid, phloroglucinaldehyde 2-O-glucoside, acylglycosides and derivatives of 2,4,6-trihydroxyphenylacetic acid and 3,5,7-trihydroxycoumarin. Based on the product distribution observed and on the impact of added Fe2+ ions and H2O2, possible degradation mechanisms are discussed. They likely start with a one- or two-electron transfer from the anionic base (a major colored form in neutral solution) to O2. The hydrogen peroxide produced could then further react as an electrophile with the anionic base and/or the hemiketal (major colorless hydrated form).This contribution to understanding the degradation mechanisms of anthocyanins around neutrality can open up new stabilization strategies to extend the range of their food applications to neutral media.

A straightforward approach for the synthesis of novel fused thiopyrano [2, 3-b] indole derivatives from the Intramolecular Friedel-Crafts acylation

In this research, a facile and efficient protocol for the regioselective synthesis of fused thiopyrano [2,3-b]indole-2-carboxylates using Eaton’s reagent (P2O5/MeSO3H) as an inexpensive, and easily available catalyst is developed under solvent-free condition at 80C. The reaction of various acetylenecarboxylates and indoline-2-(3H)-thiones using Eaton’s reagent affords fused indole heterocyclic compounds in good to excellent yields. This new method Compared to the Intramolecular Friedel-Crafts acylation has advantages of short reaction times, regioselectivity and ease of product isolation.

Microwave Irradiation Effect on Intermolecular and Intramolecular Friedel-Crafts Acylation Reaction

The effect of microwave irradiation on the intermolecular and intramolecular Friedel-Crafts acylation of aromatic compounds was investigated. Microwave irradiation had no effect on the intermolecular reaction but had an accelerating effect on the intramolecular reaction. This enhanced intramolecular reactivity that was attributed to the high probability of close proximity between the reaction sites.

Synthesis of O-Acyl Isopeptides: Stepwise and Convergent Solid-Phase Synthesis.

The O-acyl isopeptide method was developed for the preparation of difficult sequence-containing peptides, whose hydrophobic nature hampers both peptide chain construction on resin and purification with HPLC after deprotection. In the O-acyl isopeptide method, the target peptide is synthesized in an O-acyl isopeptide form, which contains an O-acyl isopeptide bond instead of the native N-acyl peptide bond at a hydroxy group-containing amino acid residue, such as Ser or Thr. The hydrophilic O-acyl isopeptide can be isolated, e.g., as a lyophilized TFA salt. The target peptide can be quantitatively obtained by a final O-to-N intramolecular acyl migration reaction with exposure to neutral conditions. Additionally, the O-acyl isopeptide is important as a hydrophilic precursor peptide for biological peptide assays that are difficult to handle. This chapter describes the synthesis of such O-acyl isopeptides by stepwise and convergent Fmoc solid-phase peptide synthesis.

A multifunctional metal–organic framework containing chiral centers for effectively and rapid removing anionic dye from aqueous solution

A novel metal-organic framework (MOF), namely, {[ZnL(bibp)]·2H2O}n (1) where H2L ​= ​1-(4-Carboxy-benzyl)-5-oxo-pyrrolidine-2-carboxylic acid, bibp ​= ​4,4′-bis(imidazol-1-yl)biphenyl, have been synthesized under solvothermal condition. In the reaction, the N-(2-carboxylbenzyl)-l-glutamic acid first undergoes intramolecular acylation to form 1-(4-Carboxy-benzyl)-5-oxo-pyrrolidine-2-carboxylic acid, which further reacts to form Compound 1. Its structure have been characterized by single-crystal X-ray diffraction analysis, elemental analysis, infrared spectroscopy and thermogravimetric analysis. Compound 1 exhibits a 3D framework with 5-fold interpenetrated dia topological network. In addition, dye adsorption experiment results indicated that compound 1 has good adsorption effect on methyl orange (MO) and can selectively adsorb and separate MO in a short time.