An efficient synthesis of 3-aryl-2-aryl(or methyl)sulfanylbenzo[b]thiophenes via cyclization of aryl 2-aryl(or methyl)sulfanylmethylsulfanylphenyl ketones

A convenient method for the preparation of 2-aryl(or methyl)sulfanylbenzo[b]thiophenes has been developed. Thus, aryl 2-aryl(or methyl)sulfanylmethylsulfanylphenyl ketones, easily prepared from readily available aryl 2-sulfanylphenyl ketones or 2-chloro-5-nitrophenyl phenyl ketone, are treated with LDA in 1,2-dimethoxyethane (DME) to give 3-aryl-2-aryl(or methyl)sulfanylmethylsulfanyl-2,3-dihydrobenzo[b]thiophen-3-ols, which in turn were dehydrated with thionyl chloride to afford 3-aryl-2-aryl(or methyl)sulfanylbenzo[b]thiophenes in reasonable overall yields.     

CIDNP as the proof of a radical mechanism of the reactions of Grignard reagents with diazonium salts

The PMR spectrum recorded during the reaction of tert-butylmagnesium chloride with p-chlorophenyl diazonium tetrafluoborate shows the CIDNP effect in the spectra of the the reaction products. Enhanced absorption and emission (the multiplet effect) has been observed for the protons of the vinyl group of isobutylene and the methyl protons of isobutane. The reaction of these diazonium salts with benzylmagnesium chloride results in only one polarised product, chlorobenzene. Such a polarisation proves the radical mechanism of the reaction which started with one-electron transfer from the Grignard reagent to the diazonium salt.     

Palladium-catalyzed redox cascade for direct β-arylation of ketones

Herein we report a full article about the detailed design and development of two palladium-catalyzed redox cascade methods that enable direct β-arylation of ketones. Palladium-catalyzed ketone dehydrogenation, aryl-X bond activation and conjugate addition were merged into a redox-neutral catalytic cycle. Non-metal-based aryl electrophiles were used as both the oxidant and the aryl source. The β-arylation with aryl iodides was achieved site-selectively with Pd(TFA)₂/P(i-Pr)₃ as the precatalyst and AgTFA as the iodide scavenger. Both cyclic and linear ketones can react to give β-aryl ketones with excellent functional group tolerance. The β-arylation with diaryliodonium salts was realized without stoichiometric heavy metal additives, and proved to be redox-neutral. A wider substrate scope regarding aryl groups and ketones was obtained for the arylation with diaryliodonium salts, and the possible involvement of palladium nanoparticles as the active catalyst was examined and discussed.     

Room‐Temperature,Ligand‐ and Base‐Free Heck Reactions of Aryl Diazonium Salts at Low Palladium Loading: Sustainable Preparation of Substituted Stilbene Derivatives

The Pd(OAc)₂‐catalyzed Heck reaction of aryl diazonium salts with 2‐arylacrylates led to cis‐stilbenes with good to excellent stereoselectivity. The environmentally friendly protocol developed in this work features low palladium loading in technical‐grade methanol at room temperature under base‐, additive‐, and ligand‐free conditions. The same protocol applied to simple Heck coupling of aryl diazonium salts with methyl acrylate allows astonishingly low palladium loading, down to 0.005 mol %. The stereoselectivity experimentally observed for the synthesis of cis‐stilbenes has been rationalized by DFT calculations. Moreover, the role of methanol in promoting the reaction has been clarified by a computational study.     

Polymerization of vinyl monomers with salts of bronsted acids

The polymerization of vinyl monomers (N-phenylmaleimide, acrylamide, acrylonitrile, methyl vinyl ketone, methyl methacrylate, vinyl chloride, and styrene) with sodium salts of Brønsted acids (sodium cyanide, sodium nitrite, sodium hydroxide, etc.) were investigated at 0°C in dimethylformamide. N-Phenylmaleimide, acrylonitrile, and methyl vinyl ketone were found to undergo polymerization with sodium cyanide, however the other monomers were not polymerized with this salt. In the polymerizations of acrylonitrile and N-phenylmaleimide with sodium cyanide, the rates of the polymerizations were found to be proportinal to the initiator concentration and to the square of the monomer concentration. The activation energy of acrylonitrile polymerization was 3.7 kcal/mole, and that of N-phenylmaleimide ws 3.0 kcal/mole. The results of the copolymerization of acrylonitrile with methyl methacrylate at 0°C in dimethyl-formamide with sodium cyanide confirm that these polymerizations proceeded by an anionic mechanism initiated by the Michael addition reaction of the monomers with the salts. In these polymerizations, the monomer reactivity increased with increase in the e values. The initiation ability of sodium salts increased with increasing pK_a of the conjugate acids and with decreasing electronegativity of metal ion in the series of lithium, sodium, and potassium cyanide. The polymerizations took place only in aprotic polar solvents, and did not occur in weak polar solvents and in protonic solvents.     

Studies on the reaction of organotin phenoxides with ethyl propiolate catalysed by triethylamine and tin(IV) chloride

Different tributyltin phenoxides react at room temperature with ethyl propiolate in benzene, in the presence of tin(IV) chloride, triethylamine and their mixture to give the derivatives of 3‐phenoxyacrylic acid ethyl ester. Exceptionally, 3‐(2‐hydroxyphenyl)acrylic acid ethyl ester and 3‐(2‐hydroxy‐5‐methylphenyl)acrylic acid ethyl ester have been obtained from the reaction of tributylphenoxytin and tributyl(p‐tolyloxy)tin, respectively catalysed by SnCl₄, and they have been easily hydrolysed to coumarin and 6‐methylcoumarin. Copyright © 2007 John Wiley & Sons, Ltd.     

Palladium‐Catalyzed Cross‐Coupling of Styrenes with Aryl Methyl Ketones in Ionic Liquids: Direct Access to Cyclopropanes

The combined use of Pd(OAc)₂, Cu(OAc)₂, and dioxygen in molten tetrabutylammonium acetate (TBAA) promotes an unusual cyclopropanation reaction between aryl methyl ketones and styrenes. The process is a dehydrogenative cyclizing coupling that involves a twofold C? H activation at the α‐position of the ketone. The substrate scope highlights the flexibility of the catalyst; a reaction mechanism is also proposed.     

Iodine-mediated one-pot synthesis of C-3 acylated indolizines from pyridines,aryl methyl ketones and acrylate derivatives

An I₂/CuI-promoted multi-component reaction from pyridines, aryl methyl ketones and electron deficient acrylates has been accomplished in a “one-pot” manner, which provides a straightforward and efficient access to C-3 acylated indolizines. The key intermediate of N-ylides is hypothesized to be generated in situ from pyridines and (hetero)aryl methyl ketones in the presence of iodine. This method has been applied in the synthesis of two molecules with anticonvulsant and anti-inflammatory activities.     

A Modified and Green Procedure for the Synthesis of β-Amido Ketones Using a BrΦnsted-Acidic Ionic Liquid as Novel and Reusable Catalyst

A green and improved method for the synthesis of β‐amido ketones through one‐pot multi‐component reaction of an enolizable ketone, aryl aldehyde, acetonitrile or benzonitrile in the presence of trimethylsilyl chloride using 3‐methyl‐1‐(4‐sulfonic acid)butylimidazolium hydrogen sulfate [(CH₂)₄SO₃HMIM][HSO₄], a Br?nsted‐acidic ionic liquid, as an effective and recyclable catalyst is described. The present methodology offers several advantages such as simple procedure with an easy work‐up, relatively short reaction time, and good to excellent yields.     

Effect of pentaerythritol and organic tin with calcium/zinc stearates on the stabilization of poly(vinyl chloride)

The stabilization effect of calcium and zinc stearates (CaSt₂/ZnSt₂) combined with pentaerythritol (PeE) and organic tin on poly(vinyl chloride) was investigated. The results show that the addition of calcium/zinc stearates combined with PeE and organic tin can improve thermal and colour stability of poly(vinyl chloride) in both static and dynamic tests. Mechanisms for improving stability of PVC are also discussed. The increase of stabilizing effectiveness of calcium/zinc stearates is ascribed to the synergistic effect between CaSt₂/ZnSt₂ and PeE and the interaction between organic tin and double bonds formed during the degradation of PVC. There is no synergistic action between organic tin and PeE or organic tin and calcium/zinc stearates.     

Iodoarene-catalyzed one-pot preparation of 2,4,5-trisubstituted oxazoles from alkyl aryl ketones with mCPBA in nitriles

2,4,5-Trisubstituted oxazoles could be easily prepared in moderate yields by the reaction of alkyl aryl ketones, iodoarene, m-chloroperbenzoic acid, and trifluoromethanesulfonic acid in acetonitrile, propionitrile, butyronitrile, and isobutyronitrile, respectively. Here, reactive aryliodonium I(III) species is formed in situ by the reaction of iodoarene with mCPBA and trifluoromethanesulfonic acid, and the formed aryliodonium I(III) species reacts with alkyl aryl ketone to form β-keto aryliodonium species. This in turn, reacts with nitrile to form the corresponding oxazole. Iodoarene works as a catalyst. However, one equivalent of iodoarene is required because one equivalent of reactive aryliodonium I(III) species must be formed prior to the reaction with alkyl aryl ketone. Then, by introducing an ionic liquid group into iodoarene, to form ionic liquid-supported iodoarene, the isolation procedure of oxazole could be simplified. The addition of ethyl acetate to the reaction mixture, washing of the reaction mixture with aq NaHCO₃, removal of ethyl acetate, and extraction of the residue with ether provided oxazoles in moderate purity, and the residual ionic liquid-supported iodoarene could be reused in the same reaction.     

THE BAYLIS—HILLMAN REACTION: TiCl4 MEDIATED COUPLING OF ALKYL VINYL KETONES WITH α-KETO ESTERS AND ALDEHYDES

TiCl₄ mediated coupling of alkyl vinyl ketones with α-keto esters and aldehydes provides respectively 2-aryl-2-hydroxy-3-methylene-4-oxoalkanoates and (Z)-keto allyl chlorides in 1 h time at room temperature. Similar coupling of trifluoromethyl phenyl ketone with methyl vinyl ketone produces 1,1,1-trifluoro-2-hydroxy-2-phenyl-3-methylenepentan-4-one.     

Studies in the field of oxygen-containing heterocycles

2-Chloro- and 2,3-dichlorotetrahydropyrans add to vinyl acetate in the presence of SnCl₄ with the formation of the corresponding gem-acetoxychlorides. The addition of 2-chlorotetrahydropyran to isopropenyl acetate is accompanied by the splitting out of HCl and the formation of the corresponding substituted enol acetate. The reaction products have been hydrolyzed to aldehydes and ketones.For Communication XIII, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 7, pp. 871–873, July, 1970.     

Synthese von Pyrano[3,2-b][1]benzopyranen aus 1-Nitroglycalen

Synthesis of Pyranol [3,2-b][1]benzopyrans from 1-Nitroglycals A synthesis of pyrano[3,2-b][l]benzopyrans β-addition of salicylic aldehyde to 1-nitroglycals, followed by a Henry reaction, is described. This sequence gave the cis-annelated pyranobenzopyranes 9 and 11 from 5 in 54 and 9% yield, respectively, demonstrating the pronounced diastereoselectivity of the β-addition. Reductive denitration of the crude product mixture yielded 14 (75%), 15 (15%), and 16 (7%), which were oxidized to the aryl ketones 20 and 21 , respectively. Reduction of 20 (NaBH₄) gave exclusively 15 . The ketone 20 was deprotected to 22 and 23 .     

Ruthenium-catalyzed reduction of racemic tricarbonyl(η-aryl ketone)chromium complexes using transfer hydrogenation: A simple alternative to the resolution of planar chiral organometallics

Racemic planar chiral (η⁶-aryl ketone)Cr(CO)₃ complexes (aryl ketone = 1-indanone, 1-tetralone, 4-chromanone and thiochroman-4-one) were prepared by refluxing the aryl ketone with Cr(CO)₆ in a 10:1 mixture of dibutyl ether and THF. The reductions of the organometallic ketones by transfer hydrogenation in 2-propanol containing KOH and the catalyst precursor, generated from [RuCl₂(η⁶-benzene)]₂ and (−)-ephedrine, resulted in optically active syn-(R,S)-(η⁶-aryl alcohol)Cr(CO)₃ and (R)-(η⁶-aryl ketone)Cr(CO)₃ compounds in 31-97% ee. Reduction of racemic (η⁶-thiochroman-4-one)Cr(CO)₃ with the catalyst precursor generated from (+)-norephedrine, instead of (−)-ephedrine, inverted the configuration of the products obtained. Syn-(S,R)-(η⁶-thiochroman-4-ol)Cr(CO)₃ and (S)-(η⁶-thiochroman-4-one)-Cr(CO)₃ were isolated in 49% and >95% ee, respectively. The free aryl ketones were reduced using the same conditions as their respective chromium complexes, giving aryl alcohols in high ee (>95%). Reactions of non-rigid acetophenone, propriophenone and their tricarbonylchromium complexes resulted in moderate to low ee.     

ROP of L-lactide and ε-caprolactone catalyzed by tin(ii) and tin(iv) acetates–switching from COOH terminated linear chains to cycles

The catalytic potential of tin(II)acetate, tin(IV)acetate, dibutyltin-bis-acetate and dioctyl tin-bis-acetate was compared based on polymerizations of L-lactide conducted in bulk at 160 or 130°C. With SnAc₂ low-Lac/Cat ratios (15/1–50/1) were studied and linear chains having one acetate and one carboxyl end group almost free of cyclics were obtained. Higher monomer/catalyst ratios and lower temperatures favored formation of cycles that reached weight average molecular weights (Mw's) between 100,000 and 2,500,000. SnAc₄ yielded mixtures of cycles and linear species under all reaction conditions. Dibutyltin- and dioctyl tin bis-acetate yielded cyclic polylactides under most reaction conditions with Mw's in the range of 20,000–80,000. Ring-opening polymerizations performed with ε-caprolactone showed similar trends, but the formation of COOH-terminated linear chains was significantly more favored compared to analogous experiments with lactide. The reactivity of the acetate catalysts decreased in the following order: SnAc₂ > SnAc₄ > Bu₂SnAc₂ ~ Oct₂SnAc₂.     

The polymerization of acrylates using a combination of a carbonyl compound and an amine as a photo-initiator system

Photo-initiator systems for the polymerization of acrylates, based on a mixture of an aryl ketone and an α,ω-diaminoalkane, have been investigated. Rate constants for the photoreduction of fluorenone by α,ω-diaminoalkanes have been evaluated: it was found that CH₃N groups are more relative than CH₃CH₂N groups. The relative rates of photo-oxidation of α,ω-diaminalkanes sensitised by benzophenone have been determined. Surprisingly, little correlation exists between the susceptibility of an amine towards oxidation and its ability to reduce excited carbonyl groups. Several mixtures composed of an aryl ketone and an α,ω-diaminoalkane were found to initiate the polymerization of methyl methacrylate. The efficiency of initiation appears to be related to the efficiency of reaction of the triplet carbonyl compound with the amine. The efficiency of a particular combination of an aryl ketone and an amine to cure films of acrylate oligomers is also governed to some extent by the efficiency of reaction of the triplet carbonyl compound with the amine. However, the structure of the amino alkyl radical produced in the initiation reaction appears to be of greater importance in determining the efficiency of polymerization. Radicals of the type R₂N?HCH₂OR were found to be highly efficient.     

Syntheses and radical polymerizations of novel optically active vinyl and isopropenyl carbamates having L-leucine structures

Syntheses and radical polymerizations of vinyl and isopropenyl carbamates having L -leucine methyl ester structures, N-vinyloxycarbonyl-L -leucine methyl ester (VOC-L-M) and N-isopropenyloxycarbonyl-L -leucine methyl ester (IOC-L-M), were carried out. VOC-L-M and IOC-L-M were prepared by the reactions of L -leucine methyl ester with vinyl and isopropenyl chloroformates in the presence of sodium hydrogen carbonate. The radical polymerization of VOC-L-M with AIBN (1 mol %) in bulk, chlorobenzene, methanol, and N,N-dimethylformamide afforded the corresponding polymer (poly(VOC-L-M)) with M _n 7,400–19,000. Meanwhile, IOC-L-M afforded no polymer with AIBN at 60°C but afforded a polymer having low molecular weight with BPO at 80°C. The glass transition temperatures of poly(VOC-L-M) and poly(IOC-L-M) were 53 and 65°C, respectively. The 10% weight loss temperatures of poly(VOC-L-M) and poly(IOC-L-M) under nitrogen were 255 and 173, respectively. The copolymerization parameters of VOC-L-M (M₁) and vinyl acetate (M₂) were evaluated as r₁ = 0.92 and r₂ = 0.63. © 1996 John Wiley & Sons, Inc.     

Graft polymers: Chain transfer and branching

The vinyl monomers, methyl methacrylate, ethyl methacrylate, and methyl acrylate were polymerized in the presence of chlorinated rubber or poly(vinyl chloride) in homogeneous solution with benzoyl peroxide as catalyst. A graft polymer was formed by a chain-transfer reaction involving the growing polymer radicals to the backbone of chlorinated rubber or poly(vinyl chloride), in addition to homopolymer from the monomer. The homopolymer was isolated from the polymer mixture by fractional precipitation from methyl ethyl ketone solution with methanol as precipitant. The chain-transfer constants for the branching reactions were evaluated. The ratios k_p/(k_t)^1/2 for the grafting reactions were obtained by a correlation of chain-transfer constants with the extent of branching. The chain-transfer data were correlated on the basis of an extension of the Q–e scheme of Alfrey and Price to polymer–polymer transfer reactions. Specific effects due to the backbone are found to have considerable influence on the course of the chaintransfer reactions and k_p/(k_t)^1/2 of the grafting reactions.     

The Clemmensen Reduction of α, β-Unsaturated Ketones

Eleven structurally different α, β-unsaturated ketones were subjected to the Clemmensen reduction under anhydrous conditions using amalgamated zinc, hydrogen chloride in a solution of ethyl ether, and acetic anhydride. In all cases but one the formation of cyclopropyl acetates was observed. 4-Methyl-3-penten-2-one, methyl vinyl ketone, 2-isopropylidene-1-cyclopentanone, and 2-cyclohepten-1-one led to substituted cyclopropyl acetates. Stereospecific reactions were found with 2-ethylidene-1-cyclopentanone, 2-benzylidene-1-cyclohexanone, and methyl 1-cyclohexenyl ketone, whereas 3-penten-2-one, 3-methyl-3-buten-2-one, and 2-methyl-2-cyclohexen-1-one afforded mixtures of the isomeric cyclopropyl acetates. These results are interpreted in terms of the intital formation of an allylic anion which undergoes electrocyclic closure. A stereospecific course is followed when geometric constraints permitted. Exceptions are discussed.