Electron-deficient Aldehydes Research Articles

Modular Synthesis of N-Vinyl Benzotriazoles

A modular approach to N1-vinyl benzotriazoles by azide-aryne cycloadditions and Julia-Kocienski reactions is described. Reactions of azidomethyl phenyl-1H-tetrazol-5-yl (PT) sulfide with arynes gave methyl(PT-sulfanyl)-substituted benzotriazoles in 68-89% yields. Oxidation of the sulfides to the sulfones gave the benzotriazole-substituted Julia-Kocienski reagents. Olefination reactions of aldehydes and a ketone with reagents derived from benzyne, 2,3-naphthyne, and 4,5-dimethoxybenzyne precursors proceeded to give various N1-vinyl benzotriazole derivatives. Olefination stereoselectivities are tunable for electron-rich aldehydes, but not for electron-deficient aldehydes and alkanals, where they proceed with good to excellent Z-stereoselectivity.

Construction of Successive Chiral Centers Adjacent to a Chiral Tetraalkylated Quaternary Center Using an Asymmetric Aldol Reaction

The aldol reaction of 2″ with a variety of different aldehydes gave the corresponding β-lactones 4 bearing successive asymmetric centers adjacent to a chiral tetraalkylated quaternary center or the (E)-alkenes 8. The use of electronically neutral or electron-deficient aldehydes led to 4 in excellent yields with high diastereoselectivities, whereas electron-rich aldehydes performed poorly and underwent decarboxylation to afford 8.

A Facile Synthesis ofN-H- andN-Substituted Acridine-1,8-diones under Sonic Condition

Synthesis of an assembly of structurally important N-H- and N-substituted acridine-1,8-diones by CAN (ceric ammonium nitrate) catalysed one-pot four-component reaction of electron-deficient and electron-rich aromatic aldehydes and aromatic amines or ammonium acetate and dimedone or cyclohexyl-1,3-diones at 26°C under sonic condition is reported. The method is clean and energy efficient as it uses a greener method and an eco-friendly catalyst.

Elucidating the Mechanism of Reversible Oxiranations via Magnetization Transfer Spectroscopy

The reversible [2 + 1] cycloadditions between an N,N'-diamidocarbene (DAC) and eight aldehydes were examined using NMR spectroscopy. Variable temperature magnetization transfer experiments revealed higher exchange rates and lower activation barriers when electron-deficient aldehydes were employed. Likewise, competitive equilibrium studies indicated a thermodynamic preference for electron-deficient aryl and sterically unhindered alkyl aldehydes compared to more electron-rich or bulkier substrates. Collectively, these and other data collected were consistent with the oxiranation process proceeding in an asynchronous manner.

Dirhodium Carboxylates Catalyzed Enantioselective Coupling Reactions of α‐Diazophosphonates, Anilines, and Electron‐Deficient Aldehydes

Chiral dirhodium carboxylate complexes ([Rh(2)(S-PTAD)(4)] or [Rh(2)(S-PTTL)(4)]) efficiently catalyze asymmetric three-component coupling reactions of α-diazophosphonates, anilines, and electron-deficient aldehydes to give α-amino-β-hydroxyphosphonates. The high level of enantiocontrol provides evidence for the intermediacy of metal-bound ammonium ylide in the product-forming step.

ChemInform Abstract: Cationic Iron(III) Porphyrin‐Catalyzed [4 + 2] Cycloaddition of Unactivated Aldehydes with Simple Dienes.

Cationic iron(III) porphyrin was found to be an efficient catalyst for the highly chemoselective hetero-Diels–Alder-type reaction of aldehydes with 1,3-dienes. The catalyzed process did not require the use of electron-deficient aldehydes such as glyoxylic acid derivatives or activated electron-rich 1,3-dienes such as Danishefsky’s diene and Rawal’s diene. The high functional group tolerance and robustness of the catalyst were demonstrated. Further, the potential utility of the catalyst was demonstrated by performing the cycloaddition in the presence of water and by carrying out cycloaddition of an unactivated ketone such as cyclohexanone with a diene.

Cationic Iron(III) Porphyrin-Catalyzed [4 + 2] Cycloaddition of Unactivated Aldehydes with Simple Dienes

Cationic iron(III) porphyrin was found to be an efficient catalyst for the highly chemoselective hetero-Diels-Alder-type reaction of aldehydes with 1,3-dienes. The catalyzed process did not require the use of electron-deficient aldehydes such as glyoxylic acid derivatives or activated electron-rich 1,3-dienes such as Danishefsky's diene and Rawal's diene. The high functional group tolerance and robustness of the catalyst were demonstrated. Further, the potential utility of the catalyst was demonstrated by performing the cycloaddition in the presence of water and by carrying out cycloaddition of an unactivated ketone such as cyclohexanone with a diene.

Mild generation of selenolate nucleophiles by thiol reduction of diselenides: convenient syntheses of selenyl-substituted aryl aldehydes

Various selenyl-substituted aryl aldehydes were obtained using dithiothreitol (DTT) as a reducing agent for diselenides in the presence of a base. For electron-deficient haloaryl aldehydes, a weak base, such as K 2CO 3, performed well. However, for electron-rich haloaryl aldehydes, a stronger base, such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), was required for successful substitution. The selenyl-substitution of heteroaryl substrates were also investigated to obtain satisfactory yields of the desired products.

Synthesis of β‐Hydroxy α‐Sulfanyl Esters by Using Nanocrystalline Magnesium Oxide

AbstractAldol‐type reaction between electron deficient aldehydes and sulfonium salts to afford the corresponding β‐hydroxy α‐sulfanyl esters in moderate‐to‐good yields by using nanocrystalline MgO is described. The sulfanyl group is a useful group for further transformations in organic synthesis. Low Rf‐value isomer is anti‐configured as revealed by X‐ray diffraction study and consistent with the assignment of 1H‐NMR spectrum.

N-Heterocyclic Carbene-Mediated Oxidative Esterification of Aldehydes: Ester Formation and Mechanistic Studies

An unexpected N-heterocyclic carbene-catalyzed esterification of α,β-unsaturated aldehydes including aromatic aldehydes with reactive cinnamyl bromides in the presence of air oxygen or MnO(2) as an oxidant is described. In the presence of oxygen, halogenated and electron-deficient aldehydes react smoothly to furnish esters in good yields. Great efforts have been made on mechanistic studies to deduce a plausible mechanism, based on the experimental results and isotopic labeling experiment.

1,3-Bis(2,4,6-trimethylphenyl)imidazolium chloride in combination with triethylamine: an improved catalytic system for hydroacylation/reduction of activated ketones

A rapid, economic, and high yielding methodology has been developed for hydroacylation/reduction of activated ketones by using 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride as a catalyst in combination with triethylamine. The reaction proceeded at an ambient temperature via generating N-heterocyclic carbene in situ that interacted with the (hetero)aryl aldehyde employed. While the reduction of ketones takes place in MeOH, the hydroacylation process was found to be effective in THF for both electron rich and deficient aldehydes.

ChemInform Abstract: Synthesis of 5,6-Dihydro-4-hydroxy-2-pyrones via Formal Cycloaddition Reactions.

Abstract Synthesis of functionalized 5,6-dihydro-4-hydroxy-2-pyrones via a novel formal cycloaddition reaction between electron-deficient aldehydes and pyrandione 2 is described. Pericyclic and aldol-like pathways have been proposed.

Cyclic carbonates as sustainable solvents for proline-catalysed aldol reactions

Ethylene and propylene carbonates, which can be prepared from epoxides and carbon dioxide, are effective solvents for the proline-catalysed, 100% atom economical, asymmetric aldol reaction between enolisable and non-enolisable carbonyl compounds. The optimal cyclic carbonate to use for a particular aldol reaction along with the need for water as a cosolvent appear to be determined by the polarities of the various components present in the reaction mixture. Both cyclic and acyclic ketones can be used as the enamine precursor and react best with electron-deficient aldehydes, such as 4-nitrobenzaldehyde and pentafluorobenzaldehyde. Chemical yields of up to 99%, diastereoselectivities of up to 100% and enantioselectivities of up to 99% can be obtained. The relative and/or absolute configuration of three of the aldol products are determined unambiguously by X-ray diffraction.

Michael-Type Adducts of 3-Carbethoxycoumarins via Diels-Alder Reaction: Tandem Ring Construction of Furopyranochroman-2-one Skeletons

Diels-Alder reaction of furan with electron-deficient 3-carbethoxycoumarins gave the Michael-type adducts obtained from the rearrangement of the intermediate Diels-Alder adducts, instead of the Diels-Alder cycloadducts. Trapping of the dipolar intermediate with electron-deficient aromatic aldehydes gave a one-pot access to fused furo[3,2-b]pyranochroman-2-ones with multiple stereogenic centers. Ring opening of the lactone moiety gave a facile route to generate diverse scaffolds.

Brucine N-oxide-catalyzed Morita–Baylis–Hillman reaction of vinyl ketones: a mechanistic implication of dual catalyst system with proline

The brucine N-oxide promoted Morita-Baylis-Hillman (MBH) reaction of vinyl ketones with aldehydes has been achieved. The corresponding asymmetric version of MBH reaction was also investigated, and the electron-deficient aryl aldehydes have emerged as suitable reaction partners for vinyl ketones; where proline was employed as a co-catalyst. In this dual catalyst system, proline is believed to form iminium intermediates with electron-deficient aryl aldehydes, while the N-oxide activates vinyl ketones to provide enolates through conjugate addition. Upon the combination of these two intermediates, the MBH products with high enantioselectivities are obtained by controlling of the rate-determining step through H-bridged chair-like transition state. Intrinsically, the resulting MBH products, alcohols, are found to interfere with the formation of both intermediates, enolates and proline iminium intermediates, thus the observed enantioselectivity of products attenuates upon further reaction conversion, possibly due to autocatalysis. This current study sheds lights on the synthetic utility of iminium species, derived from electron-deficient aryl aldehydes and proline.

Rational design of visible and NIR distyryl-BODIPY dyes from a novel fluorinated platform

A new series of distyryl-BODIPY has been rationally designed and synthesised from a novel fluorinated platform, 8-pentafluorophenylBODIPY, which has enhanced reactivity in the presence of both electron rich, and for the first time, electron deficient aldehydes. The pentafluorobenzene leads to larger red shifts of absorption and emission compared to previously reported analogues. The reactivity and spectroscopic results have been rationalised with quantum mechanics calculation. The fluorescence sensitivity of one derivative to acidity is also presented.

Single-Step Conversion of Electron-Deficient Aldehydes into the Corresponding Esters in Aqueous Alcohols in the Presence of Iodine and Sodium Nitrite

The direct conversion of aldehydes into their corresponding esters in the presence of iodine and sodium nitrite in aqueous alcohols is reported. In all these reactions, alcohol serves as reactant and also as reaction medium. Almost quantitative yields were obtained with aldehydes containing electron-withdrawing substituents and heterocyclic aldehydes.

Fluorinated 1-phenyl-1H-tetrazol-5-yl sulfone derivatives as general reagents for fluoroalkylidene synthesis.

Julia-Kocienski olefination reagents 1-fluoropropyl, (cyclopropyl)fluoromethyl, 1-fluoro-2-methyl-2-propenyl, and 1-fluoro-5-hexenyl 1-phenyl-1H-tetrazol-5-yl (PT) sulfones were prepared by metalation followed by electrophilic fluorination. Although metalation-fluorination of n-propyl, 5-hexenyl, and (cyclopropyl)methyl PT-sulfones proceeded under homogeneous conditions, fluorination of 2-methyl-2-propenyl PT-sulfone required heterogeneous fluorination conditions. Condensation reactions of fluoro PT-sulfones with aldehydes resulted in fluoroalkylidenes in high yields. Screening of olefination conditions showed that stereoselectivity depended on reagent and carbonyl structure and can in many cases be tuned either toward E- or Z-selectivity. For example, LHMDS-mediated condensations of 1-fluoropropyl PT-sulfone in the presence of MgBr(2) x OEt(2) were Z-selective with electron-rich aromatic aldehydes, a hindered aromatic aldehyde, and cinnamaldehyde. Low-temperature KHMDS-mediated condensations were E-selective with electron-rich and electron-deficient aromatic aldehydes and Z-selective with n-octanal. Dialkyl, aryl alkyl, and diaryl ketones reacted as well to give fluoro olefin products in 71-99% yields.

Study of the interaction of salicyl aldehydes with epichlorohydrin: a simple, convenient, and efficient method for the synthesis of 3,6-epoxy[1,5]dioxocines

An efficient synthetic method for 3,6-epoxy[1,5]dioxocines via the condensation of salicyl aldehydes and epichlorohydrin, using benzyl triethylammonium chloride as catalyst, is described. The use of neutral or electron-deficient salicyl aldehydes in all cases was found to give 3,6-epoxy[1,5]dioxocine derivatives in good yields. The structural features were resolved by IR, NMR spectroscopy, mass spectrometry, and ultimately proved by X-ray crystallographic analysis.

P(PhCH2NCH2CH2)3N: An Efficient Lewis Base Catalyst for the Synthesis of Propargylic Alcohols and Morita−Baylis−Hillman Adducts via Aldehyde Alkynylation

Proazaphosphatrane P(PhCH(2)NCH(2)CH(2))(3)N (1a) is an efficient catalyst for the addition of aryl trimethylsilyl alkynes to a variety of aromatic, aliphatic, and heterocyclic aldehydes in THF at room temperature. The reaction conditions are mild and employ a low catalyst loading (ca. 5 mol %). Only propargylic alcohols were isolated in good to excellent isolated yields when electron-rich, electron-neutral, heterocyclic, and aliphatic aldehydes were employed, whereas beta-branched Morita-Baylis-Hillman (MBH) type adducts were isolated with electron-deficient aromatic aldehydes after conventional acid hydrolysis of the TMS ether products. Alkynes containing heterocyclic and aromatic groups bearing electron-withdrawing or -donating substituents underwent clean addition to cyclohexanecarboxaldehyde and to electron-rich aromatic aldehydes to give propargylic alcohols in excellent isolated yields. beta-Branched Morita-Baylis-Hillman (MBH) type adducts were isolated when electron-deficient aromatic aldehydes were employed. Reaction pathways to both types of products are proposed.