One-Pot,Fluoride-Promoted Wittig Reaction

A one-pot, fluoride-promoted Wittig reaction was developed. The reactions of ethyl α-bromoacetate with aliphatic, aromatic, and heteroaromatic aldehydes in the presence of tri-n-butylphosphine and tetrabutylammonium fluoride produced α,β-unsaturated esters in good to excellent yields and E-stereoselectivity. Under the same conditions, reactions of ethyl α-bromopropionate, α-bromo acetonitrile, and α-bromoacetophenone with aliphatic and aromatic aldehydes in the presence of tri-n-butylphosphine and tetrabutylammonium fluoride produced the expected α,β-unsaturated derivatives in good E-stereoselectivity. The protocol was extended to semistabilized ylides and applied to the synthesis of some combretastatin analogs.     

Aza-Michael Addition of Amines to α,β-Unsaturated Compounds Using Molecular Iodine as Catalyst

Aza-Michael adducts are obtained in very good yields by the conjugate addition of aliphatic amines to α,β-unsaturated compounds using molecular iodine as catalyst in dichloromethane at room temperature. Aromatic amines were found to be reactive under reflux in toluene.     

One-Pot Approach to the Conversion of Alcohols into α-Iodo-α,β-unsaturated Esters

(Carboethoxymethylene)triphenylphosphorane 1 can undergo the tandem reaction of iodination–oxidation–Wittig reaction with alcohol in the presence of N-iodosuccinimide (NIS) and manganese dioxide. The reaction constitutes a stereoselective one-pot procedure for the preparation of Z-configured α-iodo-α,β-unsaturated esters in good to excellent yield.     

Synthesis of 3-Trifluoromethyl-Substituted Benzo[f]chromene Derivatives in a One-Pot Reaction

In the presence of 1,8-diazabicycolo[5.4.0]undec-7-ene (DBU) and concentrated H₂SO₄, 2-naphthol reacted smoothly with α,β-unsaturated trifluoromethyl ketones in CH₂Cl₂ at room temperature, affording the 3-trifluoromethyl-substituted benzo[f]chromene derivatives in good to excellent yields in a one-pot reaction.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource: Full experimental and spectral details].     

Synthesis of 2-Amino-4-(2-hydroxynaphthyl)-4H-chromene-3-carbonitriles by Michael Addition and Their Transformation into New Pentacyclic Compounds

2-Amino-4-(2-hydroxynaphthyl)-4H-chromene-3-carbonitriles were synthesized by Michael addition of various 3-cyanoiminocoumarins and β-naphthol in good yield. The heterocyclization of these materials in an acidic medium leads new heterocyclic compounds, which have not previously been described, in moderate to good yields and good selectivity. The synthesized compounds were characterized by infrared, ¹H NMR, ¹³C NMR, two-dimensional NMR, and elemental analysis.     

An Efficient Procedure for the Preparation of 3′-Acetyl-2′,3′-dihydrobenzothiazoles by Ring Contraction of 2′,3′-Dihydro-1,5-Benzothiazepines Under Acetylating Conditions

Reaction of 2-benzoyl-6-hydroxy-3-methyl-5-(2′-substituted-2′,3′-dihydro-1,5-benzothiazein-4′-yl) benzofurans (4a-f) with a mixture of acetic anhydride and pyridine afforded 6-acetoxy-2-benzoyl-3-methyl-5-(3′-acetyl-2′-substitutedstyryl-2′,3′-dihydrobenzothiazole-2′-yl) benzofurans (5a-f) as sole products in good yields. A reaction mechanism for the ring contraction is proposed. All the compounds (5a-f) were screened for their antifeedant activity by the “Non-Choice test method” using 6 h prestarved fourth instar larvae of Spodoptera litura F. Compounds 5a, 5c and 5d exhibited highest antifeedant activity.     

Ionic Liquid–Catalyzed Internal Redox Esterification Reaction

The internal redox esterification of α,β-unsaturated aldehydes and alcohols was carried out using different ionic liquids (ILs) as catalysts and reaction solvents. The basic ionic liquid, 1-butyl-3-methylimidazolium acetate ([bmim]OAc), exhibited the best activity for this reaction. The influences of the amount of ionic liquid catalyst and reaction time on yield of saturated ester have been investigated. The results showed that ionic liquid anions have a crucial effect on the redox esterification of α,β-unsaturated aldehydes and alcohols. The nucleophilic carbenes generated in situ from the ionic liquid cation were believed to be actual active species for this reactions.     

Concise Synthesis of α-(Hydroxymethyl) Alkyl and Aryl Vinyl Ketones

2,4-Diketoesters 2 have first been reported as starting materials for the synthesis of a new class of α-hydroxymethyl-α,β-unsaturated ketones 3. Thus, under heterogeneous liquid–liquid medium in the presence of concentrated aqueous potassium carbonate as a base, both aliphatic and aromatic 2,4-dioxoalkanoates 2 react with aqueous formaldehyde to afford the corresponding ketones 3 in fair to good yields.     

Efficient Aziridination of α,β-Unsaturated Ketones with O-(2,4-Dinitrophenyl)-hydroxylamine

The aziridination of α,β-unsaturated ketones with O-(2,4-dinitrophenyl)-hydroxylamine and tertiary amine was developed. trans-Aziridines were obtained exclusively in good yields. The reaction is proposed to occur via an aminimide intermediate.     

Natural α-Amino Acid L-Lysine–Catalyzed Knoevenagel Condensations of α,β-Unsaturated Aldehydes and 1,3-Dicarbonyl Compounds

Knoevenagel condensations of α,β-unsaturated aldehydes and 1,3-dicarbonyl compounds were catalyzed by primary natural amino acid L-lysine. The reactions were carried out at room temperature in dimethylsulfoxide. It provides a facile entry to a wide variety of α,β,γ,δ-unsaturated dicarbonyl compounds.

Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.

Stereoselective Synthesis of (1Z,3E)-2-Ethoxycarbonyl-Substituted 1,3-Dienes via Stille Coupling of (E)-α-Stannyl-α,β-Unsaturated Esters with Alkenyl Halides

Palladium-catalyzed hydrostannylation of alkynyl esters in benzene at room temperature gives stereoselectively (E)-α-stannyl-α,β-unsaturated esters 1 in good yields. (E)-α-Stannyl-α,β-unsaturated esters 1 are difunctional group reagents that undergo Stille coupling reactions with alkenyl halides 2 in the presence of Pd(PPh₃)₄ and CuI co-catalyst to afford stereoselectively (1Z,3E)-2-ethoxycarbonyl-substituted 1,3-dienes 3 in good yields.     

o-Iodoxy Benzoic Acid–Mediated Synthesis of 3,5-Diarylisoxazoles and Isoxazole-3-carboxylic Acids

A new, convenient, ecofriendly synthesis of 3,5-diarylisoxazoles is reported from α,β-unsaturated ketoximes. Similarly, a novel synthesis of isoxazole carboxylic acids is also reported. Both the methods use efficient, environmentally friendly, and nontoxic iodoxybenzoic acid (IBX) as an oxidative cyclizing reagent. Easy procedure, environmentally benign reaction conditions, and nontoxicity are advantages to the methodology.     

One-Pot Stereoselective Synthesis of (Z)-α-Arylthio-α,β-unsaturated Ketones by Hydrostannylation–Stille Tandem Reaction of Acetylenic Sulfides

(Z)-α-Arylthio-α,β-unsaturated ketones can be stereoselectively synthesized in one pot under mild conditions, in good yields, by the palladium-catalyzed hydrostannylation of acetylenic sulfides with tributyltin hydride, followed by Stille coupling with acyl chlorides.     

Studies Toward the Stereoselective Synthesis of C13 to C21 Fragment of the Brasilinolides Family of Immunosuppressive Macrolides

The work describes our attempts to synthesize the C13 to C21 fragment of brasilinolides, a 32-membered macrolide class of molecule. The C13 to C21 segment encompasses six asymmetric centers and a pyran ketal moiety. The synthesis starts from L-malic acid, and the salient features of our asymmetric synthesis are opening of epoxide, assymmetric dihydroxylation for the creation of vic-diol, and Barbier allylation.     

Facile and Efficient Method for the Synthesis of 14-Substituted-14-H-dibenzo[a,j]xanthenes Catalyzed by Ruthenium Chloride Hydrate as a Homogeneous Catalyst

Synthesis of dibenzoxanthenes through condensation of β-naphthol with various aromatic and aliphatic aldehydes in ethanol as an ecofriendly solvent using Ru^III as catalyst is reported.

Preparation of Substituted Dihydrofluorenones by Photoisomerization of Benzotropolone Derivatives

The photoisomerization of the Diels–Alder adduct formed between tetramethylpurpurogallin and maleic anhydride is described. The process is highly stereoselective, involves the β,γ-unsaturated ketone chromophore present in the adduct, proceeds through the formation of allyl and aroyl radical intermediates, and leads to a novel substituted dihydrofluorenone in good yields.

Mild and Efficient Method for Synthesis of Eaminones Using Ytterbium Triflate as Catalyst

A mild and efficient procedure for synthesis of β-enaminones by the condensation of β-dicarbonyl compounds and amines using ytterbium triflate [Yb(OTf)₃] as catalyst is described. The catalyst can be easily recovered and reused without loss of activity.     

Colloidal Palladium Nanoparticles with In Situ H2: Reducing System for α,β-Unsaturated Carbonyl Compounds

A new reducing system comprising Pd(OAc)₂ and NaBH₄ in methanol to generate palladium nanoparticles has been efficiently utilized to reduce a variety of unsaturated carbonyl compounds. These were reduced to their corresponding saturated alcohols and fully saturated compounds in selected cases. This protocol presents alternative and mild reaction conditions for reduction.     

Efficient Protocol for Stereoselective Epoxidation of Cinnamic Esters Using TsNBr2

An efficient method has been developed for the synthesis of epoxide from cinnamic esters without any catalyst. The reaction was performed in CH₃CN–water (4:1) using N,N-dibromo-p-toluenesulfonamide (TsNBr₂) in alkaline conditions. This procedure can be utilized for stereoselective synthesis of epoxides from cinnamic esters in excellent yield in a shorter reaction time with exclusive formation of the trans-isomer. The method was further extended successfully for styrenes.