Aldol Type Research Articles

4-Aza Cyclopentenone Prostaglandin Analogues: Synthesis and NF-kBInhibitory Activities.

Inspired by the cyclopentenone family of prostaglandins, a series of 4-aza, cross-conjugated cyclopentenones is described. Synthesised from N-protected (4R)-aza-cyclopentenone 5, the exocyclic alkene was installed using a modified Baylis-Hillman type aldol reaction, whereby carbon-carbon bond formation is accompanied by dehydration. In this manner octanal and octenal, for example, can be introduced to mimic the w-group present in the natural prostaglandins. Similarly, a focused range of alternative substituents were introduced using different aldehydes and ketones. The presence of the tert-butyloxycarbonyl (Boc) group on the 4-amino-cyclopentenone substituent enabled subsequent derivatisation and various electrophiles were successfully incorporated. The ability of the family of 4-amino functionalised cross-conjugated cyclopentenones to block activation of nuclear factor-kappa B (NF-kB) was studied and compared with the natural prostanoid, D12,14-15-deoxy-PGJ2 (2). Thereafter, the synthesis of a series of thiol adducts from these compounds were prepared and similarly evaluated biologically. The adducts showed comparable and, on occasion, more potent inhibition of NF-kB than their cyclopentenone precursors and generally demonstrated diminished cytotoxicity. For example, cross-conjugated dieneone 12 inhibited the activation of NF-kB with an IC50 value of 6.2 mM, whereas its endocyclic N-Boc (27) and N-acetyl (28) cysteine adducts blocked NF-kB activity with values of 1.0 and 8.0 mM respectively.

Synthesis of Alkyl Thiochromano[2,3-c]pyrrole-9-carboxylate Derivatives Utilizing Benzo[b]thiofuran-2,3-dione, Maleimides, and Alkyl Alcohol/Water Mixtures

AbstractA set of thiochromano[2,3-c]pyrrolidine-1,3-diones, incorporating α-hydroxy esters and their acids at the C-9 position, was prepared via direct interaction involving benzo[b]thiofuran-2,3-diones, maleimides, and alkyl alcohols in water at 90 °C. Structures of the new products were deduced from HRMS and NMR spectral data and confirmed by single-crystal X-ray crystallography. An insight into a proposed pathway involving a sequential Michael conjugate addition (initiated by the sulfur atom) and an aldol-type reaction is presented.

Recent Developments on Brønsted Acid Catalyzed Asymmetric Aldol Reactions and the Fate of the Catalysts

Since the innovative work of Terada and Akiyama, asymmetric reaction using chiral Brønsted acid has attracted great attention. Asymmetric aldol reactions are extensively studied in different organocatalysis. Brønsted acid-catalyzed aldol reaction may be carried out directly without modification of the substrates or Mukaiyama type aldol reaction using silyl enol ether as nucleophiles. The reaction may proceed through the formation of enol intermediate followed by the attack to the electrophile while Mukaiyama type aldol reactions may follow two mechanistic pathways- Brønsted acidic pathways where Brønsted acid directly activates the substrate or Lewis acid pathways where Brønsted acid acts as pre-catalyst. Here, the recent advancement of asymmetric aldol reactions using chiral Brønsted acid as a catalyst and the fate of the catalysts in the reaction has been discussed in this review. It is observed that some kinds of aldol reactions have rarely been studied and need more attention.

Rap‐Stoermer Reaction: TEA Catalyzed One‐Pot Efficient Synthesis of Benzofurans and Optimization of Different Reaction Conditions

AbstractThe reaction of substituted salicylaldehydes with α‐haloketones to obtain benzofuran‐2‐yl (Alkyl/aryl) ketones, which is a Dickman type aldol condensation product in base, solvent, and temperature environment, is called as Rap‐Stoermer reaction. In this study, a series of Benzofuran‐2‐yl (Alkyl/ aryl) ketones was synthesized by heating substituted salicylaldehydes and α‐haloketones under solvent‐free sealed (closed vessel) conditions by using triethyleamine (TEA) as a novel base catalyst in good to excellent yields (81–97 %) at 130 °C and the obtained results compared with the existing literature. The reaction conditions were optimized in terms of yield, time, base, solvent temperature, stoichiometric ratios, and synthesis environments (open or closed vessels). The optimized protocol offers promising advantages such as solvent‐free and clean reaction media, short reaction time, no byproducts, and appreciable high yields for the prospective studies. Characterization of the synthesized compounds was performed by using spectroscopic methods such as ATR‐FTIR, 1H‐NMR, 13C‐NMR and LC‐MS.

The Synthesis of 3-(R)- and 3-(S)-Hydroxyeicosapentaenoic Acid.

Monohydroxylated polyunsaturated fatty acids belonging to the oxylipin class of natural products are present in marine and terrestrial sources as well as in the human body. Due to their biological activities and role in diverse biosynthetic pathways, oxylipins biosynthesized from eicosapentaenoic acid and arachidonic acid have attracted great interest from the scientific community. One example is 3-hydroxyeicosapentaenoic acid where the absolute configuration at C-3 has only been tentatively assigned. In this paper, studies on acetate type aldol reactions that enabled the preparation of 3-(R)-hydroxyeicosapentaenoic acid (3R-HETE, 2) and its enantiomer are presented.

Regiodivergent Functionalization of Isoquinoline‐1,3(2H,4H)‐dione Derivatives via Aerobic Umpolung

AbstractA mild and green methodology for the regiodivergent functionalization of isoquinoline‐1,3(2H,4H)‐diones under aerobic conditions was developed. Under a catalytic amount of base, heteroatom nucleophiles went through an imide opening/ring contraction sequence to give the thermodynamic controlled product; while carbon based nucleophiles led to kinetic controlled aldol type product. Moreover, the aldol type product was transformed into the benzo[c]phenanthridine core structures under transition metal free condition, which provides an environmental benign access to this framework.

Synthesis of the 4-aza cyclopentenone analogue of Δ12,14-15-deoxy-PGJ2 and S-cysteine adducts

The synthesis of a series of 4-aza cross-conjugated cyclopentenones, inspired by the natural prostaglandin Δ12,14-15-deoxy-PGJ2 (5) is described. Using the 4-aza cyclopentenone 7, the installation of the α-side chain was performed using N-functionalisation, following a Boc-deprotection. The ω-side chain was then installed through a Baylis-Hillman type aldol reaction with trans-2-octenal. This afforded 11, the aza-analogue of 5. With this prostaglandin analogue in hand, a series of thiol adducts (14–16) were prepared. Included are activities for compounds 11 and 14–16 in relation to inhibition of the transcription factor NF-κB.

Total Synthesis of the Natural Herbicide MBH‐001 and Analogues

The first total synthesis of the natural herbicide MBH‐001 (1) is reported. Structurally it is a 2‐methyloxazol‐5(2H)‐one with a (1‐hydroxyethyl) substituent at the 2‐position. By relying on cyclic nitrones, a flexible route to MBH‐001 and relevant analogues was developed. Key steps include the reaction of a 2‐hydroxyimino ester with an aldehyde to form a 5‐oxo‐2,5‐dihydrooxazole 3‐oxide. In an aldol‐type reaction, the anion of these cyclic nitrones reacted with an aldehyde at the 2‐position. A final reduction of the nitrone to the corresponding imine using zinc led to the target compounds. The cyclic nitrones are also accessible by reacting an α‐keto acid with an oxime. These two versatile synthetic routes enabled us to prepare the first MBH‐001 analogues for structure activity relationship analysis of the herbicidal efficacy. Thus, furthering our aim of developing new herbicides to tackle the ever‐growing problem of weed resistance.

A Green Protocol for the Synthesis of α‐Diazo‐β‐hydroxyesters and One‐Pot Conversion to β‐Keto‐Esters and Imidazo[1,2‐a]pyridine‐3‐carboxylates

AbstractA new solvent cum reagent system comprising of water extract of banana ash and dimethylsulfoxide (WEB‐DMSO) has been engaged for the first time to promote the aldol type condensation reaction of aldehydes with ethyl diazoacetate. The condensation reaction has smoothly undergone producing a range of α‐diazo‐β‐hydroxy esters in good to excellent yields. The solvent system has been reused up to five times without loss of its catalytic activity. Further, two one‐pot sequential reactions have been developed in the same reaction medium. First, the methodology has been extended to synthesize β‐keto esters through Pd catalyzed 1,2‐hydrogen migration. Secondly, β‐keto esters have been converted to imidazo[1,2‐a]pyridine‐3‐carboxylates by using N‐bromosuccinimide and 2‐aminopyridines in a one‐pot fashion.

Synthesis and characterization of cinnamylidene acetone – A study on tuning of band gap by vibrational spectroscopic tools

The title molecule Cinnamylidene acetone (CA) was synthesized through a single step base catalyzed aldol type condensation between acetone and cinnamaldehyde. The prepared molecule has been characterized using NMR (1H and 13C) spectral analysis, FTIR, UV–Vis and Elemental analysis. The complete vibrational characterization of the molecule was performed using experimental (FTIR and FT-Raman) spectra and calculations at DFT level. In order to carry out a detailed vibrational spectroscopic analysis of CA, Fourier Transform Infrared and Fourier Transform Raman spectra recorded in condensed phase were used. To determine the optimized geometry and vibrational wavenumbers, Density functional theory calculations in the B3LYP/6-31G** level have been carried out followed by scaling using the scaled quantum mechanical methodology. A root mean square deviation of 6.53 cm−1 has resulted from the scaled quantum mechanical treatment. The ultraviolet visible spectra of the title compound dissolved in various solvents were recorded in the range of 300–600 nm. The natural bond orbital and frontier molecular orbital analyses were also performed using B3LYP/6-31G** method. These studies revealed a reduction in the band gap of CA in comparison with that of cinnamaldehyde (CY).

Photocatalytic C(sp3)−H Activation towards α‐methylenation of Ketones using MeOH as 1 C Source Steering Reagent

AbstractUnprecedented direct access to terminal enones via α‐methylenation of aryl ketones to form C=C bond is achieved under visible‐light conditions using methanol as one carbon source substrate and solvent as well. The reaction involves Cu@g‐C3N4‐catalysed in situ oxidation of methanol into formaldehyde followed by dehydrative cross aldol type reaction. Various aryl ketones react efficiently with MeOH, producing α,β‐unsaturated carbonyl compounds only in 4–8 h at room temperature in excellent yield (84–97%). Operational simplicity, wide substrate scope, ambient reaction conditions, visible‐light photocatalysis and novel application of MeOH as methylene donor substrate are the salient features making the envisaged protocol mild, efficient and green alternative to the existing methods for synthesis of such fine chemicals.magnified image

The Mukaiyama type aldol reaction for the synthesis of trans-2,6-disubstituted tetrahydropyrans: synthesis of diospongin A and B.

An efficient synthesis protocol for the preparation of trans-2,6-disubstituted tetrahydropyrans by the reaction of 1-phenyl-1-triemthylsiloxyethylene with six membered cyclic hemiacetals in the presence of iodine is developed. This reaction proceeds smoothly under mild conditions employing a catalytic amount of molecular iodine. The feature of this novel conversion includes milder reaction conditions, broader substrate scope, functional group tolerance and good diastereoselectivity. The efficiency and practicality of the current method were successfully displayed in the total synthesis of diospongin A and B in good yields.

Aldol-type transformations of levoglucosenone-derived medium-sized keto lactones

Action of bases on levoglucosenone-derived 6-oxononan-9-olide and 7-oxodecan-10-olide causes the transannular reaction of the aldol type affording stable 2-acylcyclopent-1-en-1-ol and 2-acylcyclohex-1-en-1-ol, respectively. The lower homologue, 5-oxooctan-8-olide derivative, under the similar conditions gives a complex mixture of products, which may be explained by the poor stability of the intermediate 2-acyl-cyclobut-1-en-1-ol.

Pyrene based chalcone as a reversible fluorescent chemosensor for Al3+ ion and its biological applications

A pyrene scaffold bearing a phenol molecule has been designed and synthesized as a chemosensor L1 by an aldol type of condensation reaction. The sensor showed high sensitivity and selectivity for Al3+ ions by the enhancement of fluorescene intensity and distinguishes from the other potentially competing metal ions. The effect of pH, time and the reversibility of the sensor are studied. The fluorescence experiments suggested that the proposed binding of L1 and Al3+ ion is in a 1:1 stoichiometry. The chemosensor’s direct application in the electrosorptive removal of Al3+ ion and several other biological applications including the bio-imaging of bacterial cells were examined.

Synthesis of functionalized cyclopentenes through allenic ketone-based multicomponent reactions.

A novel and efficient synthesis of diversely functionalized cyclopentene derivatives through the multicomponent reactions of 1,2-allenic ketones with 4-chloroacetoacetate and malononitrile/cyanoacetate under mild and metal-free conditions is presented. Mechanistically, the formation of title compounds involves a cascade process including nucleophilic substitution, Michael addition and intramolecular aldol type reaction. Interestingly, when 1-phenyl allenic ketones bearing electron-donating groups on the phenyl ring were reacted with 4-chloroacetoacetate and cyanoacetate, methylenecyclo-pentanes, the regioisomer of cyclopentenes, were formed with good selectivity and high efficiency.

Synthesis of Functionalized Pyridines via Cu(II)-Catalyzed One-Pot Cascade Reactions of Inactivated Saturated Ketones with Electron-Deficient Enamines.

In this paper, a novel and efficient synthesis of 3-acylpyridines and pyridine-3-carboxylates through the oxidative one-pot sequential reactions of inactivated saturated ketones with electron-deficient enamines is presented. Mechanistically, the formation of the title compounds involves the in situ formation of an enone intermediate through an oxidative dehydrogenation of the saturated ketone substrate, followed by its [3+3] annulation with β-enaminone or β-enaminoester via a cascade process, including Michael addition, aldol type condensation, and oxidative aromatization.

Ambident Reactivity of Nitroso Compounds for Direct Amination and Hydroxylation of Carbonyls

Functionalization of carbonyls, particularly with a heteroatom subunit, is an important synthetic transformation. Utilization of ambident electrophiles for such a strategy is advantageous because two different heteroatom units can be installed from a single source under judicial reaction conditions. Recently, there have been increased examples for the construction of C–O and C–N bonds using nitroso compounds, a prototype of ambident electrophiles. In this short review, we discuss the advantages and challenges of exploiting nitroso compounds in organic synthesis with specific focus on nitroso aldol type processes for the direct hydroxylation and amination of carbonyl compounds.1 Introduction2 Prime Challenges in Nitroso Aldol Reactions3 Direct Hydroxylation Reactions4 Direct Amination Reactions5 Conclusion and Outlook

Microwave-Assisted Synthesis of Tetrahydrocarbazole Linked 1,2-Diazoles in Aqueous-Brønsted Acid Catalytic System

A new series of tetrahydrocarbazole coupled 1,2-diazoles 4/5/6(a–o) in moderate to excellent yield was synthesized successfully via multicomponent reaction approach by adopting Michael type-addition of hydrazines on in situ generated α,β-unsaturated ketones via aldol type strategy under synthetic microwave radiations and conventional heating. Structural confirmations of all the prepared compounds were achieved by spectroscopic techniques. The best results were achieved when equal amounts of water-acetic acid were used in microwave conditions in 4 minutes.

ChemInform Abstract: A Ru(III) — Catalyzed α‐Cross‐Coupling Aldol Type Addition Reaction of Activated Olefins with Isatins.

A α-cross-coupling aldol type addition reaction activated olefins with isatins has been described in the presence of ruthenium(III) chloride and tributyltin hydride (TBTH) at room temperature. This method is found to work consistently for the delivering of ene-carbonyl coupled products in good to excellent yields with moderate to acceptable selectivity. The substrate scope of the present method was briefly discussed.

A Ru(iii) – catalyzed α-cross-coupling aldol type addition reaction of activated olefins with isatins

A α-cross-coupling aldol type addition reaction activated olefins with isatins has been described in the presence of ruthenium(iii) chloride and tributyltin hydride (TBTH) at room temperature.