Palladium‐Catalyzed Cascade CH Trifluoroethylation of Aryl Iodides and Heck Reaction: Efficient Synthesis of ortho‐Trifluoroethylstyrenes

A palladium‐catalyzed selective C? H bond trifluoroethylation of aryl iodides has been explored. The reaction allows for the efficient synthesis of a variety of ortho‐trifluoroethyl‐substituted styrenes. Preliminary mechanistic studies indicate that the reaction might involve a key Pd^IV intermediate, which is generated through the rate‐determining oxidative addition of CF₃CH₂I to a palladacycle; the bulky nature of CF₃CH₂I influences the reactivity. Reductive elimination from the Pd^IV complex then leads to the formation of the aryl–CH₂CF₃ bond.     

Palladium‐Catalyzed Cascade C?H Trifluoroethylation of Aryl Iodides and Heck Reaction: Efficient Synthesis of ortho‐Trifluoroethylstyrenes

A palladium‐catalyzed selective C H bond trifluoroethylation of aryl iodides has been explored. The reaction allows for the efficient synthesis of a variety of ortho‐trifluoroethyl‐substituted styrenes. Preliminary mechanistic studies indicate that the reaction might involve a key Pd^IV intermediate, which is generated through the rate‐determining oxidative addition of CF₃CH₂I to a palladacycle; the bulky nature of CF₃CH₂I influences the reactivity. Reductive elimination from the Pd^IV complex then leads to the formation of the aryl–CH₂CF₃ bond.     

Transition-Metal-Free Controllable Single and Double Difluoromethylene Formal Insertions into C−H Bonds of Aldehydes with TMSCF2Br

We have developed a new strategy for controllable single and double difluoromethylene (CF₂) formal insertions into C−H bonds of aldehydes with nearly full selectivity under transition-metal-free conditions. The key to the success of controllable CF₂ insertions lies in the well-defined formation of 2,2-difluoroenolsilyl ether and 2,2,3,3-tetrafluorocyclopropanolsilyl ether intermediates using difluorocarbene reagent TMSCF₂Br (TMS=trimethylsilyl). These two intermediates can react with various electrophiles including proton sources and various halogenation reagents, allowing for the access to diverse arrays of ketones containing difluoromethylene (CF₂) and tetrafluoroethylene (CF₂CF₂) units. The first synthesis of relatively stable 2,2,3,3-tetrafluorocyclopropanolsilyl ethers has been achieved, which offers a new platform to explore other unknown chemical space.     

Taming elemental fluorine: Indirect use of fluorine for the synthesis of α-fluoroketones[1]

Fluorine and sodium trifluoroacetate react at ?75° to produce a variety of fluoroxy-compounds. Although it is possible to direct the reaction towards the formation of CF₃COOF or CF₃CF₂OF, mixtures may be used when only the electrophilic fluorine has to be attached to the molecule of interest. Such is the case of the reaction of enol-acetates with the mixture of the fluoroxy reagents. A wide variety of compounds, including steroids and containing various functional groups, were tested. In most cases the desired α-fluoroketones were obtained in good to very good yields. The new fluorine containing compounds are the compounds numbered $\text{2, 9, 11, 13, 15, 16}$ and $\text{20}$.     

The coupling of potassium organotrifluoroborates with Baylis–Hillman derivatives via visible-light photoredox catalysis

Catalyzed by Ir[dF(CF₃)ppy]₂(dtbbpy)PF₆, the coupling of potassium organotrifluoroborates with Baylis–Hillman derivatives under visible light irradiation has been developed. Based on the mechanism of reductive quenching cycle, it provides an easy, mild, efficient method for the synthesis of a variety of α,β-unsaturated carboxylic esters derivatives in a broad scope of the substrates.     

Group 3 metal (Sc, La) triflates as catalysts for the carbomethoxylation of aliphatic amines with dimethylcarbonate under mild conditions

The activity of Sc(OTf)₃ and La(OTf)₃ (OTf=SO₃CF₃) as catalysts for the phosgene-free synthesis of carbamate esters via carbomethoxylation of aliphatic amines with dimethylcarbonate (DMC) has been investigated. In the presence of M(OTf)₃ (M=Sc, La), primary and secondary aliphatic amines easily react with dimethylcarbonate, under very mild conditions (20 °C), to afford carbamate esters with good yield and excellent selectivity (≌100%). Sc(OTf)₃ is a more effective catalyst than the homologue La salt. The carbomethoxylation reaction requires as strict anhydrous conditions, as, at 20 °C, the presence of water inhibits markedly the catalytic activity of both triflate salts. Temperature influences carbamate selectivity, which is lower at higher temperature because of deleterious formation of N-methylation side-products.     

Aryl trifluoromethyl acetylenes

A wide variety of aryl trifluoromethyl acetylenes may be prepared in high yield by allowing CF₃CCZnCl, generated from CF₃CCH, to react with aryl iodides a catalytic amount of tetrakis(triphenylphosphine)-palladium.     

Trifluoromethylboranes and -borates: new synthetic strategies and applications

The synthesis of salts with the [B(CF₃)₄]⁻ anion has been the starting point for new developments in the field of trifluoromethylboron chemistry. In contrast to the previous syntheses of (CF₃)_nB derivatives (n=1–3), achieved exclusively by CF₃ transfer, the synthesis of the [B(CF₃)₄]⁻ anion was accomplished by fluorination of the [B(CN)₄]⁻ anion with ClF or ClF₃ in anhydrous HF. Owing to its thermal and chemical stability, [B(CF₃)₄]⁻ is an attractive weakly coordinating anion. However, in concentrated sulfuric acid one of the four CF₃ groups is solvolyzed to a CO ligand to yield the neutral borane carbonyl (CF₃)₃BCO. It has been shown that the borane carbonyl compound is a versatile synthetic building block, and numerous reactions have been investigated. The addition of nucleophiles to the C atom of the CO ligand is favored, and examples for new derivatives are the anions [(CF₃)₃BCPnic]⁻ (Pnic=N, P, As). Under certain conditions, ligand-exchange reactions are also observed, for example, the formation of (CF₃)₃BNCH. Finally, the borane carbonyl compound is a component of the conjugated Brønsted–Lewis superacid HF/(CF₃)₃BCO.     

Tetrafluorine‐Containing Ketones and Acetoacetates: Synthesis and Mechanistic Study

Addition of trimethylsilyl trifluoroacetate to the carbanions of α‐fluorobenzyl‐phosphonate ( 3 ) or diisopropyl(fluorocarbethoxymethyl)phosphonate ( 9 ) formed the corresponding intermediates [CF₃C(O)CFPh]^?Li⁺ ( 10 ) and [CF₃C(O)CFCO₂Et]^?Li⁺ ( 11 ), respectively. Subsequent protonation, alkylation or allylation of 10 and 11 afforded trifluoromethyl fluorobenzyl ketones 12 and ethyl 2,4,4,4‐tetra‐fluoroacetoacetates 13 . Based on the results obtained, a plausible mechanism was proposed.     

Synthesis and photophysical properties of benzo[c]thiophene,p-phenylene-, triphenylamine-, and pyrene-based vinylenes

An efficient synthesis of benzo[c]thiophenyl/p-phenylenyl/pyrenyl phosphonate esters has been achieved using ZnBr₂-catalyzed Michaelis–Arbuzov reaction of corresponding benzyl alcohol/bromides at room temperature. Horner–Wadsworth–Emmons reaction of the phosphonate esters with aryl/heteroaryl aldehydes in the presence of t-BuOK furnished the vinylenes in good yields. The absorption and emission characteristics of the synthesized vinylenes were also reported.     

Heterocyclic and acyclic derivatives of F-N-isopropylacetimidoyl chloride

$\text{F}$-N-Isopropylacetimidoyl chloride, CF₃CClNCF(CF₃)₂, has been used as a precursor for a variety of heterocyclic and acyclic compounds. Reaction with azide ion yields a mixture of the imidoyl azide, CF₃(N₃)CNCF(CF₃)₂, and the 1,5-tetrazole, CF₃$\text{CNNN}$CF(CF₃)₂. Hexafluoropropylideniminolithium produces as a minor product the conjugated diimine, (CF₃)₂CNC(CF₃)NCF(CF₃)₂, from nucleophilic attack at the imidoyl chlorine and as a major product the triimine, (CF₃)₂CNC(CF₃)NC(CF₃)₂NC(CF₃)₂, from further attack at the isopropyl fluorine. A thio-amide, CF₃C(S)NHCH(CF₃)₂, and a Δ³-1,2,4-dithiazoline, $\text{SSC(CF}{}_3\text{)NC}$(CF₃)₂, are produced upon reaction of hyrogen sulfide with the imidoyl chloride. Pathways are proposed for each of the reactions.     

Trivalent-pentavalente Phosphorverbindungen/Phosphazene. V. Darstellung,Eigenschaften und Reaktionen neuer Phosphonig- und Phosphinigsäureester

Trivalent-Pentavalent Phosphorus Compounds/Phosphazenes. V. Preparation, Properties, and Reactions of New Phosphonous- and Phosphinous Acid Esters Phosphonous diesters R? P(OR′)₂ (R ? CH₃, Ph and R′ ? CH₂? CF₃) have been synthetized by reaction of phosphonous dichlorides with 2, 2, 2-trifluoroethanol in the presence of a base. These diesters react with trimethyl(trimethylsilylimino)phosphorane, (CH₃)₃P?N? Si(CH₃)₃ by desilylation and N? P-linking to phosphinous acid esters (CH₃)₃P?N? P(OR′)R. The phosphinous acid esters react with methyl iodide to the quaternary salts [(CH₃)₃P? N? P(OR′)(R)CH₃]⁺I^?. The compounds are characterized by elementary analysis and spectroscopical methods.     

P and H NMR studies of the transesterification polymerization of polyphosphonate oligomers

Polymeric phosphonate esters are an interesting class of organophosphorus polymers because both the polymer backbone and phosphorus substituents can be modified. These polymers have been prepared by ring-opening polymerizations of cyclic phosphites, stoichiometric polycondensations of dimethyl phosphonate with diols in conjunction with diazomethane treatment and by transesterification of polyphosphonate oligomers. Our initial attempts to prepare high molecular weight polymeric phosphonate esters by the transesterification methods were unsuccessful. Results indicate that the reactions of dimethyl phosphonate with diols to form polyphosphonate oligomers with only methyl phosphonate end groups are plagued by a serious side reaction that forms phosphonic acid end groups. These end groups do not participate in the transesterification reaction and limit the molecular weights of the polymers that can be obtained. The phosphonic acid end groups can be converted into reactive methyl phosphonate end groups by treatment with diazomethane, however diazomethane is explosive and the polymerization is slow. An alternative route for the production of high molecular weight polymers is the transesterification of the 1,12-bis(methyl phosphonato)dodecane, formed by the reaction of excess dimethyl phosphonate and 1,12-dodecanediol, with a Na₂CO₃ promoter. This allows polymers with molecular weights of up to 4.5×10⁴ to be prepared, and no phosphonic acid end groups are observed in these polymers. Thermal analyses of the poly(1,12-dodecamethylene phosphonate) have shown that this polymer has reasonable thermal stability (onset of thermal decomposition at 273 °C). This polymer also undergoes a cold crystallization process at 15 °C similar to that which has been observed in some polyesters, polyamides and elastomers.     

Effective IR Laser Conversion of Carbon-13 Enriched Chlorodifluoromethane to Dibromodifluoromethane

Infrared laser conversion of chlorodifluoromethane (CF₂HCl) enriched in ¹³C to 31%, to dibromodifluoromethane (CF₂Br₂) with the same enrichment has been studied. Optimum conditions have been found, and effective laser synthesis of macroscopic amounts (1 g) of CF₂Br₂ has been carried out. IR absorption spectra of synthesized CF₂Br₂ with a ¹³C concentration of 31% have been recorded. The ¹³C isotope shifts of the ν₁, ν₆, and ν₈ modes have been measured.     

Genaration of a η6- arene/Cr(co)3-complexed diazonium ion; homolytic and heterolytic dediazoniation via metallic π-bonded aryl radicals and cations

The reaction of NO⁺ with o-toluidinechromium tricarbonyl has been studied. Diazotization (attack on N) competes with NO⁺ attack on the metal and decarbonylation. The Cr(CO)₃-complexed diazonium ion is unstable and dediazoniates even at low temperature. The dediazoniation mechanism is predominantly homolytic. Competing heterolytic dediazoniation is observed in highly ionizing, low nucleophilicity solvents such as CF₃SO₃H (TfOH), FSO₃H and CF₃CH₂OH (TFE).     

IR laser-induced dehydrohalogenation of halogenated ethanes

Pulsed IR radiation from a CO₂ TEA laser has been shown to cause dehydrohalogenation of CF₃CH₃, CF₂ClCH₃ and C₂H₅Cl under collisionless conditions. IR emission has been observed and is attributed to HF² and CF₂CH₂² from CF₃CH₃, and to HF² and HCl² from CF₂ClCH₃.     

Der 2-Trimethylsilyläthyl-Rest als selektiv abspaltbare Carboxy-Schutzgruppe

The 2-trimethylsilylethyl residue, a selectively cleavable carboxyl protecting group In a search for new carboxyl protecting groups suitable for use in peptide synthesis, 2-trimethylsilylethyl esters [-COOCH₂CH₂Si(CH₃)₃] of several N-protected amino acids have been prepared. These esters can be synthesized in good yields from N^a-benzyloxycarbonyl-amino acids and 2-trimethylsilylethanol with dicyclohexylcarbodiimide in the presence of pyridine. They are stable under a wide variety of conditions used during coupling and work-up in peptide synthesis. For removal the 2-trimethylsilylethyl group is readily cleaved by fluoride ions, preverably using a quaternary ammonium fluoride in dimethylformamide. Some side reactions which occurred during the removal of the 2-trimethylsilylethyl group are discussed. Special attention has been paid to the question of racemization during the treatment with fluoride ions. No. evidence of racemization was found in any of the cases examined.     

Negative ion formation in CF2Cl2, CF3Cl and CFCl3 following low energy (0—10 eV) impact with near monoenergetic electrons

Negative ion formation in CF₂Cl₂, CF₃Cl and CFCl₃ under low-energy electron impact has been investigated using a trochoidal monochromat The ions observed are F^?, Cl^?, FCl^?, Cl₂^?, CFCl₂^? from CF₂Cl₂; F^?, Cl^?, FCl^?, CF₂Cl Quoting available thermochemical data, it can be shown that most of the observed negative ions arise from dissociative attachment processes. Appearance The extremely high yield of Cl^? in CFCl₃, which is observed at ε = 0.0 eV, will be discussed with regard to the lifetime of this molecule i     

Superacid-catalyzed reactions of pyridinecarboxaldehydes

A variety of pyridinecarboxaldehydes are shown to give condensation products in high yields (80-99%, 10 examples) by reacting with benzene and CF₃SO₃H (triflic acid). In the superacidic solution, pyridinecarboxaldehydes can react with deactivated arenes (o-dichlorobenzene and nitrobenzene) and with saturated hydrocarbons (methylcyclohexane and adamantane). Dicationic intermediates from pyridinecarboxaldehydes in superacid (FSO₃H-SbF₅) have been directly observed using low temperature ¹³C NMR spectroscopy. Diprotonated pyridinecarboxaldehydes have also been studies using ab initio computational methods.     

Oxydifluoromethylation of Alkenes by Photoredox Catalysis: Simple Synthesis of CF2H‐Containing Alcohols

We have developed a novel and simple protocol for the direct incorporation of a difluoromethyl (CF₂H) group into alkenes by visible‐light‐driven photoredox catalysis. The use of fac‐[Ir(ppy)₃] (ppy=2‐pyridylphenyl) photocatalyst and shelf‐stable Hu's reagent, N‐tosyl‐S‐difluoromethyl‐S‐phenylsulfoximine, as a CF₂H source is the key to success. The well‐designed photoredox system achieves synthesis of not only β‐CF₂H‐substituted alcohols but also ethers and an ester from alkenes through solvolytic processes. The present method allows a single‐step and regioselective formation of C(sp³)–CF₂H and C(sp³)?O bonds from C=C moiety in alkenes, such as hydroxydifluoromethylation, regardless of terminal or internal alkenes. Moreover, this methodology tolerates a variety of functional groups.