Enolizable Aldehydes Research Articles

Diastereoselective Base-Catalyzed Formal [4 + 2] Cycloadditions of N-Sulfonyl Imines and Cyclic Anhydrides.

A diastereoselective base-catalyzed Mannich reaction of cyclic, enolizable anhydrides and N-sulfonyl imines for the synthesis of δ-lactams is reported. This anhydride Mannich reaction tolerates imines derived from aryl and enolizable aldehydes. A base-catalyzed product epimerization pathway ensures high anti diastereoselectivity in aryl and achiral enolizable imines.

Reaction of azides and enolisable aldehydes under the catalysis of organic bases and Cinchona based quaternary ammonium salts

Herein we report a two-step sequence for the preparation of amides starting from azides and enolisable aldehydes. The reaction proceeded via the formation of triazoline intermediates that were converted into amides via Lewis acid catalysis. Preliminary studies on the preparation of triazolines under chiral phase transfer catalysis are also presented, demonstrating that enantioenriched amides could be prepared from achiral aldehydes in moderate to low enantioselectivity.

Zinc cation supported on carrageenan magnetic nanoparticles: A novel, green and efficient catalytic system for one‐pot three‐component synthesis of quinoline derivatives

This is the first report of supporting zinc cation on ƛ‐carrageenan/Fe3O4 magnetic nanoparticles. The structural and magnetic properties of this hybrid (Zn2+/ƛ‐carrageenan/Fe3O4 nanoparticles) were identified using various techniques. This green and efficient catalytic system was applied in the synthesis of biologically important quinolines. The products were obtained in good to high yields (52–95%) from a one‐pot reaction procedure involving aromatic aldehydes, enolizable aldehydes and aniline derivatives. Our method has many advantages such as mild reaction conditions, easy work‐up, use of a reusable magnetic catalyst and high yields of products.

Enantioselective Rhodium-Catalyzed Allylic Alkylation of Prochiral α,α-Disubstituted Aldehyde Enolates for the Construction of Acyclic Quaternary Stereogenic Centers.

A highly enantioselective rhodium-catalyzed allylic alkylation of prochiral α,α-disubstituted aldehyde enolates with allyl benzoate is described. This protocol provides a novel approach for the synthesis of acyclic quaternary carbon stereogenic centers and it represents the first example of the direct enantioselective alkylation of an aldehyde enolate per se. The versatility of the α-quaternary aldehyde products is demonstrated through their conversion to a variety of useful motifs applicable to target-directed synthesis. Finally, mechanistic studies indicate that high levels of asymmetric induction are achieved from a mixture of prochiral (E)- and (Z)-enolates, which provides an exciting development for this type of transformation.

ChemInform Abstract: Solvent‐Free Multicomponent Synthesis of Biologically‐Active Fused‐Imidazo Heterocycles Catalyzed by Reusable Yb(OTf)3 Under Microwave Irradiation.

A rapid, efficient and solvent-free – green – protocol for Groebke–Bienayme–Blackburn reaction (G−B-B reaction) for the synthesis of fused-imidazo heterocycles has been developed. The methodology reported here involves multi-component reaction (MCR) catalyzed by reusable Yb(OTf)3 (a mild and water-compatible Lewis acid) under microwave irradiation which allows fast and efficient preparation of the title compounds in excellent yield. The salient features of our protocol are solvent-free, low catalyst loading (2.5–0.1 mol%) with good turnover number (TON: 890) and turnover frequency (TOF: 178/min), less reaction time (5 min), no dependency over specialized purification (by either column chromatography or recrystallization) and very high isolated yield (95–99 %) with excellent green chemistry metrics (E-factor: 0.071 and Mass Intensity: 1.071). The water compatibility of the catalyst Yb(OTf)3 has been exploited for its efficient recovery through water washings. In addition, the other exciting milestones of the protocol are catalyst and workup solvent recycling, excellent conversion with notorious substrates such as enolizable aldehyde or isonitrile bearing reactive substituent, very efficient at higher scale (50 mmol) and easy to couple with other methods (one-pot two-step cyclization: G−B-B reaction and Ullmann-type coupling).

Asymmetric Synthesis of Methylphenidate and Quinolizidinones by Addition of Aldehydes to Piperidine-Based Conjugated N-Acyl­iminium Ions

The synergistic effect of Lewis acids and MacMillan organocatalyst allows the α-regioselective and enantioselective α-amidoalkylation of piperidine derivatives with enolizable aldehydes. The potentiality of the synthetic method is illustrated by a short asymmetric synthesis of the eutomer of the blockbuster drug Ritalin and by a concise formal synthesis of 1-alkyl-4-substituted quinolizidine alkaloids.

Zn(OTf)2-Mediated Expeditious and Solvent-Free Synthesis of Propargylamines via C–H Activation of Phenylacetylene

Zn(OTf)2-mediated expeditious and solvent-free synthesis of propargylamines via A3 coupling of aldehydes, amines, and phenylacetylene has been described. The described protocol proceeds effectively with variety of substituted benzaldehydes, enolizable aldehyde, and formaldehyde. Recyclability of the catalyst, low catalyst loading, and use of inexpensive catalyst are the key features of the present protocol.

One-pot synthesis of quinoline derivatives using choline chloride/tin (II) chloride deep eutectic solvent as a green catalyst

In this work, various quinoline derivatives were prepared efficiently through a one-pot, three component synthesis using choline chloride/tin(II) chloride (ChCl·2SnCl2) deep eutectic solvent (DES) as a green catalyst. The procedure is free of using toxic solvents or catalyst and it could be categorized as a green method. In this procedure, aniline derivatives, aromatic aldehydes and enolizable aldehydes were mixed in the presence of DES that plays both roles of solvent and the reaction catalyst. Using this methodology, quinoline derivatives were synthesized simply at 60°C in 2–3h with high yields (54–97%). All products were purified by chromatography and recrystallization in ethanol. The employed DES have been recycled 4 time without important loss of its activity.

Solvent–free Multicomponent Synthesis of Biologically–active Fused–imidazo Heterocycles Catalyzed by Reusable Yb(OTf)3 Under Microwave Irradiation

AbstractA rapid, efficient and solvent‐free – green – protocol for Groebke–Bienaymé–Blackburn reaction (G−B‐B reaction) for the synthesis of fused‐imidazo heterocycles has been developed. The methodology reported here involves multi‐component reaction (MCR) catalyzed by reusable Yb(OTf)3 (a mild and water‐compatible Lewis acid) under microwave irradiation which allows fast and efficient preparation of the title compounds in excellent yield. The salient features of our protocol are solvent‐free, low catalyst loading (2.5–0.1 mol%) with good turnover number (TON: 890) and turnover frequency (TOF: 178/min), less reaction time (5 min), no dependency over specialized purification (by either column chromatography or recrystallization) and very high isolated yield (95–99 %) with excellent green chemistry metrics (E‐factor: 0.071 and Mass Intensity: 1.071). The water compatibility of the catalyst Yb(OTf)3 has been exploited for its efficient recovery through water washings. In addition, the other exciting milestones of the protocol are catalyst and workup solvent recycling, excellent conversion with notorious substrates such as enolizable aldehyde or isonitrile bearing reactive substituent, very efficient at higher scale (50 mmol) and easy to couple with other methods (one‐pot two‐step cyclization: G−B‐B reaction and Ullmann‐type coupling).

Development of a syn-Selective Mannich Reaction of Aldehydes with Propargylic Imines by Dual Catalysis: Asymmetric Synthesis of Functionalized Propargylic Amines.

Direct coupling of enolizable aldehydes with C-alkynyl imines is realized affording the corresponding propargylic Mannich adducts of syn configuration, thus complementing previous methods that gave access to the anti-isomers. The combination of proline and a urea Brønsted base cocatalyst is key for the reactions to proceed under very mild conditions (3-10 mol % catalyst loading, dichloromethane as solvent, -20 °C, 1.2 molar equivalents of aldehyde) and with virtually total stereocontrol (syn/anti ratio up to 99:1; ee up to 99 %). Some possibilities of further chemical elaboration of adducts are also briefly illustrated.

Bifunctional Brønsted Base Catalyzes Direct Asymmetric Aldol Reaction of α‐Keto Amides

AbstractThe first enantioselective direct cross‐aldol reaction of α‐keto amides with aldehydes, mediated by a bifunctional ureidopeptide‐based Brønsted base catalyst, is described. The appropriate combination of a tertiary amine base and an aminal, and urea hydrogen‐bond donor groups in the catalyst structure promoted the exclusive generation of the α‐keto amide enolate which reacted with either non‐enolizable or enolizable aldehydes to produce highly enantioenriched polyoxygenated aldol adducts without side‐products resulting from dehydration, α‐keto amide self‐condensation, aldehyde enolization, and isotetronic acid formation.

Bifunctional Brønsted Base Catalyzes Direct Asymmetric Aldol Reaction of α-Keto Amides.

The first enantioselective direct cross-aldol reaction of α-keto amides with aldehydes, mediated by a bifunctional ureidopeptide-based Brønsted base catalyst, is described. The appropriate combination of a tertiary amine base and an aminal, and urea hydrogen-bond donor groups in the catalyst structure promoted the exclusive generation of the α-keto amide enolate which reacted with either non-enolizable or enolizable aldehydes to produce highly enantioenriched polyoxygenated aldol adducts without side-products resulting from dehydration, α-keto amide self-condensation, aldehyde enolization, and isotetronic acid formation.

Nucleophilic arylation with tetraarylphosphonium salts

Organic phosphonium salts have served as important intermediates in synthetic chemistry. But the use of a substituent on the positive phosphorus as a nucleophile to construct C–C bond remains a significant challenge. Here we report an efficient transition-metal-free protocol for the direct nucleophilic arylation of carbonyls and imines with tetraarylphosphonium salts in the presence of caesium carbonate. The aryl nucleophile generated from phosphonium salt shows low basicity and good nucleophilicity, as evidenced by the successful conversion of enolizable aldehydes and ketones. The reaction is not particularly sensitive to water, shows wide substrate scope, and is compatible with a variety of functional groups including cyano and ester groups. Compared with the arylmetallic reagents that are usually moisture sensitive, the phosphonium salts are shelf-stable and can be easily handled.

Asymmetric synthesis of bicyclic dihydropyrans via organocatalytic inverse-electron-demand oxo-Diels-Alder reactions of enolizable aliphatic aldehydes.

A highly enantioselective organocatalytic inverse-electron-demand oxo-Diels-Alder reaction involving aqueous acetaldehyde has been discovered. The reaction, in which cyclic enones serve as dienes in the presence of readily available secondary amine catalysts, allows facile construction of optically active bicyclic dihydropyrans. Other typical enolizable aliphatic aldehydes can also serve as competent dienophiles in the reaction.

Cascade oxime formation, cyclization to a nitrone, and intermolecular dipolar cycloaddition.

Simple haloaldehydes, including enolisable aldehydes, were found to be suitable for the formation of cyclic products by cascade (domino) condensation, cyclisation, dipolar cycloaddition chemistry. This multi-component reaction approach to heterocyclic compounds was explored by using hydroxylamine, a selection of aldehydes, and a selection of activated dipolarophiles. Initial condensation gives intermediate oximes that undergo cyclisation with displacement of halide to give intermediate nitrones; these nitrones undergo in situ intermolecular dipolar cycloaddition reactions to give isoxazolidines. The cycloadducts from using dimethyl fumarate were treated with zinc/acetic acid to give lactam products and this provides an easy way to prepare pyrrolizinones, indolizinones, and pyrrolo[2,1-a]isoquinolinones. The chemistry is illustrated with a very short synthesis of the pyrrolizidine alkaloid macronecine and a formal synthesis of petasinecine.

ChemInform Abstract: Enantioselective Functionalization of Inactive sp3 C—H Bonds Remote to Functional Group by Metal/Organo Cooperative Catalysis.

AbstractThe method serves for the [4 + 2]‐cyclization of aliphatic enolizable aldehydes with quinone derivatives in the presence of molecular oxygen as oxidant and a prolinol‐derived chiral catalyst.

ChemInform Abstract: A Convenient Modification of the Fischer Indole Synthesis with a Solid Acid.

AbstractA wide range of enolizable aldehydes and ketones and various substituted phenylhydrazines are converted to the corresponding indoles using the cation exchange resin Amberlite IR 120 as catalyst.

ChemInform Abstract: I2‐Mediated Oxidative Cyclization for Synthesis of Substituted Indolizines.

A direct method for the synthesis of substituted indolizines by means of I2-mediated oxidative tandem cyclization via C–N/C–C bond formation was developed. Various substituted aromatic/aliphatic enolizable aldehydes and 2-pyridylacetates/acetonitrile/acetone proceeded smoothly in this transformation, and the desired products were generated in moderate to good yields.

ChemInform Abstract: An Organocatalytic Azide—Aldehyde [3 + 2] Cycloaddition: High‐Yielding Regioselective Synthesis of 1,4‐Disubstituted 1,2,3‐Triazoles.

An organocatalytic azide–aldehyde [3+2] cycloaddition (organo-click) reaction of a variety of enolizable aldehydes is reported. The organo-click reaction is characterized by a high rate and regioselectivity, mild reaction conditions, easily available substrates with simple operation, and excellent yields with a broad spectrum of substrates. It constitutes an alternative to the previously known CuAAC, RuAAC, and IrAAC click reactions.

ChemInform Abstract: FeCl3·6H2O‐Catalyzed Mukaiyama‐Aldol Type Reactions of Enolizable Aldehydes and Acetals.

AbstractA general procedure for the title condensation of dimethylacetals derived from enolizable aldehydes with silyl enol ethers is developed using FeCl3 as the catalyst.