A Regioselective Synthesis of Benzopinacolones through Aerobic Dehydrogenative α‐Arylation of the Tertiary sp3 CH Bond of 1,1‐Diphenylketones with Aromatic and Heteroaromatic Compounds

A regioselective synthesis of symmetrical and unsymmetrical benzopinacolones through aerobic dehydrogenative α‐arylation at the tertiary sp³ C?H bond of substituted 1,1‐diphenylketones with aromatic and heteroaromatic compounds, in the presence of K₂S₂O₈ in CF₃COOH at room temperature, is described. The reaction is proposed to go via a carbocation intermediate, which could be generated directly from cleavage of the sp³ C?H bond of 1,1‐diphenylketone. Subsequent α‐arylation was achieved at the methene sp³ carbon atom of the substituted ketone. A variety of substituted aromatic and heteroaromatic compounds were compatible with this reaction. In addition, benzopinacolones were converted into sterically hindered, tetrasubstituted alkenes and polycyclic aromatic compounds.     

SYNTHESE POLYCYCLISCHER [C]-ANELLIERTER THIOPHENE

Abstract

A benzene ring substituted with two acyl groups in ortho-position was built from α-dicarbonyl compounds and dibenzyl ketone via Diels-Alder reaction of the intermediate cyclopentadienones with 1,2-diaroyl acetylenes and subsequent decarbonylation. The polycycles which were synthesized in this way formed interesting new [c]-annellated thiophenes on reaction with tetraphosphorus decasulfide (P₄S₁₀).     

Transition metal-catalyzed formation of CF3-substituted α,β-unsaturated alkene and the synthesis of α-trifluoromethyl substituted β-amino ester

A new transition metal-catalyzed formation of CF₃-substituted α,β-unsaturated alkenes through the ylide intermediate from the reaction between methyl 3,3,3-trifluoro-2-diazopropionate 1 and aryl aldehydes has been developed. Further transformation of the alkene affords the α-trifluoromethyl substituted β-amino ester, a valuable intermediate in the synthesis of fluorine-containing amino acids with potential biological application.     

Cross-aldol reactions of levoglucosenone and its derivatives with cyclohex-1-en-1-ol ethers

The reaction of levoglucosenone with cyclohex-1-en-1-yl trimethylsilyl ether under Mukaiyama reaction conditions gave [1 + 2]-Michael–aldol condensation product with participation of the acetal center. The reaction was accompanied by opening of the 1,6-anhydro bridge and intramolecular hemiketalization by the hydroxy group of the 2-oxocyclohex-1-enyl fragment. Under analogous conditions, dihydrolevoglucosenone gave rise to four diastereoisomeric 1,2-addition products. Internal cyclohex-1-en-1-ol ether obtained by treatment of the Michael adduct of levoglucosenone and cyclohexanone with Ac₂O–ZnCl₂ underwent intramolecular Mukaiyama reaction involving substituted α-carbon atom of the cyclohexanone fragment and acetal moiety to afford spiro derivative and product of subsequent AdE1 acetylation of intermediate α′-cyclohexenyl ether fragment.     

TeCl4 as a catalyst in cationic oligomerisations and polymerisations

TeCl₄ catalyses the oligomerisation and polymerisation of certain substituted phenylethylenes and substituted benzyl chlorides. The catalysis is cationic, TeCl₄ acting as a Lewis acid. The termination of polymerisation of the substituted ethylenes is by an internal Friedel-Crafts reaction, whereas that of the substituted benzyl chlorides is by reaction with chloride ions. Contrary to the usual reactivity sequence, stilbene was found to be more reactive than α-methylstyrene in the TeCl₄-catalysed polymerisations.     

Michael-Type Addition Reactions of Some Enamines to Arylidenepyrazolones

The reaction of the arylidenepyrazolones (1_b-d) with l-morpholinocyclohexene (E₂) in refluxing acetonitrile leads to the less substituted alkylated enamines 3_b-d. On the other hand, the more substituted alkylated enamines 2_a-d are formed when 1_a-d react under the same conditions with l-piperidinocyclohexene (E₁). The nature of the enamine is crucial. Nucleophilic attack of the enamine on the α, β-unsaturated carbonyl system of 1 gives rise to a zwitterionic intermediate which through α -proton loss leads to different Michael-type adducts depending on the enamine.     

Catalytic Sc(OTf)3 mediated direct asymmetric aldol reaction of (−)-menthyl isothiocyanatoacetate with aldehydes by using (−)-menthol as chiral auxiliary

This method involves the direct asymmetric aldol reaction of (−)-menthyl isothiocyanatoacetate 5 with a variety of substituted aromatic aldehydes, which offers a convenient method for the synthesis of intermediate containing biologically relevant α-amino β-hydroxyl groups in oxazolidine ring. In this methodology, the products show remarkable diastereoselectivity using Sc(OTf)₃ as a catalyst and easily accessible (−)-menthol as a chiral auxiliary. This approach includes some important aspects such as mild reaction conditions, high yields, and excellent diastereoselectivity with a number of substituted aromatic aldehydes. The optimization and effect of different catalysts were studied at different reaction conditions and it is found that Sc(OTf)₃ shows excellent diastereoselectivity at −45°C.     

Reactions des derives du phosphore trivalent avec les composes a halogene positif—II : Phosphites d'alcoyle et α-cyano α-haloesters: Synthese et reactivite de cetenimines n-phosphoryles

Trialkylphosphites P(OR)₃ react with substituted α-cyano α-haloesters by initial attack of the phosphorous compound at the halogen atom to give N-phosphorylated ketenimines or a mixture of ketenimines and vinylphosphates when R = Me ou Et The reaction occurs via an intermediate ion pair. Nucleophiles (water, methanol, amines, carbanions) react with ketenimines in two ways: a phosphoryl displacement and an addition of the nucleophilic reagent. In the latter, ketenimines yield phosphoramides which, according to the nature of the substituants attached to the initial esters, can be converted into heterocycles (Δ₂ pyrrolines, pyrrolidines, furans).     

Rhodium-catalyzed α-methylthiolation reaction of unactivated ketones using 1,2-diphenyl-2-methylthio-1-ethanone for the methylthio transfer reagent

In the presence of catalytic amounts of RhH(PPh₃)₄, 1,2-bis(diphenylphosphino)ethane (dppe), and dimethyl disulfide, ketones without α-activating groups were α-methylthiolated with 1,2-diphenyl-2-methylthio-1-ethanone giving α-methylthio ketones. The reaction of unsymmetrical ketones proceeded at the more substituted carbons. The initial formation of kinetic α-methylthiolated products followed by their rearrangement to thermodynamic products was observed in the reaction of α-phenyl ketones. Aldehydes, phenylacetate, and phenylacetonitrile were also α-methylthiolated under these conditions.     

Catalytic Asymmetric Fluorination of Copper Carbene Complexes: Preparative Advances and a Mechanistic Rationale

The Cu-catalyzed reaction of substituted α-diazoesters with fluoride gives α-fluoroesters with ee values of up to 95 %, provided that chiral indane-derived bis(oxazoline) ligands are used that carry bulky benzyl substituents at the bridge and moderately bulky isopropyl groups on their core. The apparently homogeneous solution of CsF in C₆F₆/hexafluoroisopropanol (HFIP) is the best reaction medium, but CsF in the biphasic mixture CH₂Cl₂/HFIP also provides good results. DFT studies suggest that fluoride initially attacks the Cu- rather than the C-atom of the transient donor/acceptor carbene intermediate. This unusual step is followed by 1,2-fluoride shift; for this migratory insertion to occur, the carbene must rotate about the Cu−C bond to ensure orbital overlap. The directionality of this rotatory movement within the C₂-symmetric binding site determines the sense of induction. This model is in excellent accord with the absolute configuration of the resulting product as determined by X-ray diffraction using single crystals of this a priori wax-like material grown by capillary crystallization.     

A convenient procedure for the synthesis of tetrathia-[7]-helicene and the selective α-functionalisation of terminal thiophene ring

This paper describes a convenient preparation of tetrathia-[7]-helicene (TH[7]), the generation of the α-anion on the terminal thiophene ring, and the synthesis of the 2-formyl-tetrathia-[7]-helicene (2-CHO-TH[7]). The key intermediate trans-1,2-dibenzodithiophene-ethene, prepared in 97% yield by McMurry coupling of the 2-formyl-benzo[1,2-b;4,3-b′]dithiophene, was transformed into TH[7] using a known procedure. The described method affords TH[7] in 46% overall yield, which is more than four times the yield previously reported in the literature. The α-anion of TH[7], which is easily generated on the α-position of one of the terminal thiophene rings, reacts with electrophilic reagents such as D₂O and DMF. The latter reaction proved to be the best way to prepare 2-CHO-TH[7], a key intermediate for the preparation of new substituted heterohelicenes.     

Magnetic nanoparticle supported amine: An efficient and environmental benign catalyst for versatile Knoevenagel condensation under ultrasound irradiation

Amine functionalized silica coated Fe₃O₄ nanoparticles (SiO₂@MNP-A) were successfully prepared as a novel heterogeneous amine. The catalyst was characterized by XRD, FT-IR, TEM, magnetic measurement, elemental analysis and was found to be a magnetically separable and highly active catalyst for ambient Knoevenagel condensation of aromatic aldehydes and α-aromatic (heteroaromatic or polyaromatic)-substituted methylene compounds in water under ultrasonic irradiation to afford the corresponding products in good to excellent yields. Very interestingly, SiO₂@MNP-A successfully catalyze the reaction of the non-cyano substituted compound with benzaldehyde to achieve a key intermediate for the preparation of Atorvastatin calcium in green and atom-economic manner. In addition, the catalyst SiO₂@MNP-A can be reused for 8 times without any obvious loss of its activity. The role of ultrasonication in the Knoevenagel condensation was also discussed with the assistance of UV–vis spectrometry.     

Aromatic nucleophilic substitution reaction of 2,4-dinitrohalogenobenzene and ethyl α-cyano-phenylacetate benzyl anion

The aromatic nucleophilic substitution reaction of 2,4-dinitrohalogenobenzene (DNHB; halogeno =F, Cl, Br) with ethyl α-cyanophenylacetate (ECPA) benzyl anion has been studied by means of UV and IR spectrophotometry as well as gas chromatography. The rates of intermediate formation and product formation were determined respectively. In contrast with common S _N Ar reactions, the formation rate constant of the intermediates, substituted cyclohexadienates, was in the order of halogen =F>Br>Cl, whereas the rate constant of product formation was in the order F>Cl>Br, which revealed that the departure of the halogen atom was the rate-limiting step for the overall reaction in the presence of a sterically hindered nucleophile. These reactions could be catalyzed by the solvated electrons. The corresponding reaction intermediates, radical species, were detected by ESR and the reactions were proved to proceed mainly by a solvated-electron induced radical chain reaction mechanism.     

Regioselective Alkylative Carboxylation of Allenamides with Carbon Dioxide and Dialkylzinc Reagents Catalyzed by an N‐Heterocyclic Carbene–Copper Complex

The alkylative carboxylation of allenamide catalyzed by an N‐heterocyclic carbene (NHC)–copper(I) complex [(IPr)CuCl] with CO₂ and dialkylzinc reagents was investigated. The reaction of allenamides with dialkylzinc reagents (1.5 equiv) and CO₂ (1 atm.) proceeded smoothly in the presence of a catalytic quantity of [(IPr)CuCl] to afford (Z)‐α,β‐dehydro‐β‐amino acid esters in good yields. The reaction is regioselective, with the alkyl group introduced onto the less hindered γ‐carbon, and the carboxyl group introduced onto the β‐carbon atom of the allenamides. The first step of the reaction was alkylative zincation of the allenamides to give an alkenylzinc intermediate followed by nucleophilic addition to CO₂. A variety of cyclic and acyclic allenamides were found to be applicable to this transformation. Dialkylzinc reagents bearing β‐hydrogen atoms, such as Et₂Zn or Bu₂Zn, also gave the corresponding alkylative carboxylation products without β‐hydride elimination. The present methodology provides an easy route to alkyl‐substituted α,β‐dehydro‐β‐amino acid ester derivatives under mild reaction conditions with high regio‐ and stereoselectivtiy.     

Ring-opening of tertiary cyclopropanols derived from β-diketones

The ring-opening reaction of 1,2-disubstituted cyclopropanols, prepared from β-diketones, mediated by Cu(NO₃)₂, p-TsOH, and NaOH is reported. The Cu(II)-mediated ring-opening of cyclopropanols gave α-methylene-γ-diketones in good yields. The reaction took place at the less substituted carbon of the cyclopropanols, involving mild conditions and a simple procedure. The reaction induced by p-TsOH in CH₂Cl₂ afforded α-methyl-γ-diketones as the major product with minor amounts of δ-diketones. The 2,3,5-trisubstituted furans were obtained in high yields when the ring-opening reaction was mediated by p-TsOH in methanol under reflux conditions. In the presence of sodium hydroxide the reaction proceeded smoothly in preference to the formation of δ-diketones, particularly for substrates with an aromatic group on the cyclopropane.     

Oxidative synthesis of benzo[1,4]oxazines from α-branched primary amines and ortho-benzoquinones

The efficient oxidative construction of benzo[1,4]oxazines from simple α-branched amines and ortho-benzoquinones is reported. The procedure pivots on a triethylamine and iodine mediated oxidative ring closure from the ketimine intermediate formed upon their condensation. This reaction was shown to tolerate a variety of α-branched benzylamines and downstream derivatization to substituted benzomorpholine structures was also demonstrated.     

Stereoarrayed CF3‐Substituted 1,3‐Diols by Dynamic Kinetic Resolution: Ruthenium(II)‐Catalyzed Asymmetric Transfer Hydrogenation

CF₃‐substituted 1,3‐diols were stereoselectively prepared in excellent enantiopurity and high yield from CF₃‐substituted diketones by using an ansa‐ruthenium(II)‐catalyzed asymmetric transfer hydrogenation in formic acid/triethylamine. The intermediate mono‐reduced alcohol was also obtained in very high enantiopurity by applying milder reaction conditions. In particular, CF₃C(O)‐substituted benzofused cyclic ketones underwent either a single or a double dynamic kinetic resolution during their reduction.     

Palladium-Catalyzed Decarboxylative Alkynylation of α-Acyloxyketones by C(sp3)−O Bond Cleavage

Palladium-catalyzed decarboxylative alkynylation of α-acyloxyketones triggered by C(sp³)−O bond cleavage is disclosed. The decarboxylation strategy featuring a neutral reaction condition enabled an unprecedent catalytic alkynylation of a ketone enolate. The reaction was applied to a variety of substrates, giving desired products in good yields. We successfully obtained X-ray crystallography of a new palladium–enolate intermediate that was synthesized by a reaction of [Pd(cod)(CH₂TMS)₂] with XPhos and α-acyloxyketone at room temperature, indicating facile C(sp³)−O bond disconnection.     

Mukaiyama aldolisation reactions of α,β-epoxyaldehydes in aqueous media

The Mukaiyama aldolisation reaction in aqueous media of cis and trans α,β-epoxyaldehydes with tert-butyldimethylsilyl ketene acetal in the presence of Lewis's acids was studied. Sc(OTf)₃ gave the best results in terms of selectivity. The same reaction of cis and trans α,β-epoxyaldehydes with the enoxysilane of ethyl pyruvate resulted in epoxy substituted ulosonic derivatives issued from a double sequential condensation of the pyruvate on the epoxy derivatives.     

Highly Selective Arbuzov Reaction of α-Chlorocarbonyl Compounds with P(OEt)3 and Substituted Amino Urea

Abstract

A facile one—pot Arbuzov reaction of α-chlorocarbonyl compounds with P(OEt)₃ and substituted amino urea is described. The highly selective Arbuzov reaction of α-chlorocarbonyl compounds could take place under relatively mild conditions, giving products in high yields.