Recyclable Siloxy Serine Organocatalyst for the Direct Asymmetric Mannich Reactions in Ionic Liquids

A recyclable siloxy-L-serine organocatalyst has been developed to catalyze the asymmetric direct three-component Mannich reactions in ionic liquid hmim[PF₆], furnishing the β-amino carbonyl scaffold in high enantio- and diastereoselectivities. The direct Mannich reaction between a selection of aromatic aldehydes and ketones resulted in good yields and high enantioselectivities.

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.     

Organocatalyzed One-Pot Synthesis of Substituted 1,5-Benzodiazepine and Benzimidazole Derivatives

An efficient synthesis of some heterocycles is described by condensation between o-phenylenediamine and 1,3-dicarbonyl compounds catalyzed by L-proline. The reaction is carried out either at room temperature or reflux depending on the substrates.     

Improved Enantioselective Synthesis of Protected (3S,4S)-4-Amino-3,5-dihydroxypentanoic Acid (ADPA)

An improved enantioselective synthesis of protected (3S,4S)-4-amino-3,5-dihydroxypentanoic acid (ADPA) from L-serine has been developed. Enantioselectivity is improved by replacing the methyl ester with the tert-butyl ester and using neutral magnesium salt of esters to give β-keto ester.     

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.     

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.     

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].     

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.

Debromination of 4-Bromo-3-Arylsydnones with Sodium Dithionite

A variety of 4-bromo-3-arylsydnones can be debrominated with sodium dithionite in excellent yield under very mild conditions.     

Synthesis and Structure of Novel 1-Aryl-4,4,4-trichloro-1,3-butanediones

Novel 1-aryl-4,4,4-trichloro-1,3-butanediones in good yields (80–97%) were synthesized in one pot through acetal acylation with trichloroacetyl chloride followed by acid hydrolysis. Structures of all compounds were elucidated by elemental analysis, mass spectrometry, and ¹H/¹³C nuclear magnetic resonance (NMR) measurements. The ¹H/¹³C NMR data showed that trichloromethyl-β-diketones 2a–k in solution are predominantly ketoenol. However, the spectroscopic data from 4,4,4-trichloro-2-methyl-1-phenyl-1,3-butabedione (2l) with methyl substituent between carbonyls showed a bias toward the diketo form in solution. X-ray diffraction of monocrystals from 2g and 2i showed that these compounds are cis-ketoenol tautomers.

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

Efficient Strategy for the Synthesis of 4-Hydroxy-1H-pyrrole-2,3-dicarboxylic Ester Derivatives Using Transition-Metal-Oxide Catalysts

A facile and an efficient strategy for the synthesis of multisubstituted pyrrole derivatives was developed using an unusual ring annulation of dialkyl acetylene dicarboxylic ester and α-amino acids with transition-metal oxides such as mercuric(II) oxide and silver(I) oxide and complexes such as ceric ammonium nitrate (CAN) and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCI) as catalysts.     

Efficient synthesis of β-lactam containing α-hydroxy phosphonates using tartaric acid and fumaric acid as mild catalysts

A short and efficient protocol for the synthesis of β-lactam containing α-hydroxy phosphonate esters using inexpensive catalysts such as tartaric acid and fumaric acid is described.     

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.     

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.     

Overview on the phosphonation of the C=X functional groups utilizing alkyl phosphites

The main objective of this survey is to provide a comprehensive review of recent achievements related to the phosphonation processes, applying alkyl phosphites and different electrophiles (C?X, X: O, N, or C). The review discusses the important reactions of trialkyl and dialkyl phosphite reagents with a variety of aldehydes, ketones, aldimines, ketimines, hydrazones, oximes, diazo compounds, thio- and isocyanates as well as activated olefins as a convenient methodology for the synthesis of biologically important α-hydroxy- and α-aminophosphonates as well as heterocycles containing phosphorus and substituted heterocyclic phosphor esters. We are herein concentrating only on reactions that lead to phosphorylated products as they represent a vast and important research area of interest for academic, as well as for industrial, pharmaceutical and phytopharmaceutical chemists. The literature survey has been fully covered up by our group and others over the last 25 years.     

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.     

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.     

Facile synthesis of naturally occurring nor-lignans (±)-Machicendiol and its analogs

A facile synthesis of naturally occurring (±)-machicendiol and its analogs has been accomplished in moderate to good yield from 2-aryl-5-formly-7-methoxy-benzofurans through two simple, efficient approaches involving the application of Reformatsky reaction and Claisen condensation.     

Mild and Efficient Method for α-Thiocyanation of Ketones and β-Dicarbonyl Compounds Using Bromodimethylsulfonium Bromide–Ammonium Thiocyanate

An efficient and convenient method for α-thiocyanation of ketones and β-dicarbonyl compounds has been developed using a reagent combination of bromodimethylsulfonium bromide (BDMS) and ammonium thiocyanate in acetonitrile. The developed method is mild and gave good yield of the products at room temperature.