Rhodium-catalyzed silylation of ortho-functionalized aryl halides with hydrosilanes

The silylation of ortho-functionalized aryl iodide with trialkylsilanes in the presence of RhCl(CO)(PPh₃)₂ or [Rh(cod)₂]BF₄ and K₃PO₄ provides the corresponding arylalkylsilane in good to high yield. This catalytic system showed a dramatically different activity when Pd(t-Bu₃P)₂ was used as a catalyst.     

Improved synthesis of aryltriethoxysilanes via palladium(0)-catalyzed silylation of aryl iodides and bromides with triethoxysilane.

The scope of the palladium-catalyzed silylation of aryl halides with triethoxysilane has been expanded to include aryl bromides. A more general Pd(0) catalyst/ligand system has been developed that activates bromides and iodides: palladium(0) dibenzylideneacetone (Pd(dba)(2)) is activated with 2-(di-tert-butylphosphino)biphenyl (Buchwald's ligand) (1:2 mol ratio of Pd/phosphine). Electron-rich para- and meta-substituted aryl halides (including unprotected aniline and phenol derivatives) undergo silylation to form the corresponding aryltriethoxysilane in fair to excellent yield; however, ortho-substituted aryl halides failed to be silylated.     

Direct Introduction of a Dimesitylboryl Group Using Base‐Mediated Substitution of Aryl Halides with Silyldimesitylborane

The first dimesitylboryl substitution of aryl halides with a silylborane bearing a dimesitylboryl group in the presence of alkali‐metal alkoxides is described. The reactions of aryl bromides or iodides with Ph₂MeSi?BMes₂ and Na(OtBu) afforded the desired aryl dimesitylboranes in good to high yields and with high borylation/silylation ratios. Selective reaction of the sterically less‐hindered C?Br bond of dibromoarenes provided monoborylated products. This reaction was used to rapidly construct a D‐π‐A aryl dimesityl borane with a non‐symmetrical biphenyl spacer.     

Copper-Mediated Fluorination of Aryl Trisiloxanes with Nucleophilic Fluoride

A method for the nucleophilic fluorination of heptamethyl aryl trisiloxanes to form fluoroarenes is reported. The reaction proceeds in the presence of Cu(OTf)₂ and KHF₂ as the fluoride source under mild conditions for a broad range of heptamethyltrisiloxyarenes with high functional group tolerance. The combination of this method with the silylation of aryl C−H bonds enables the regioselective fluorination of non-activated arenes controlled by steric effects following a two-step protocol.     

Mechanistic Insights into Palladium‐Catalyzed Silylation of Aryl Iodides with Hydrosilanes through a DFT Study

The catalytic cycles of palladium‐catalyzed silylation of aryl iodides, which are initiated by oxidative addition of hydrosilane or aryl iodide through three different mechanisms characterized by intermediates R₃Si−Pd^II−H (Cycle A), Ar−Pd^II−I (Cycle B), and Pd^IV (Cycle C), have been explored in detail by hybrid DFT. Calculations suggest that the chemical selectivity and reactivity of the reaction depend on the ligation state of the catalyst and specific reaction conditions, including feeding order of substrates and the presence of base. For less bulky biligated catalyst, Cycle C is energetically favored over Cycle A, through which the silylation process is slightly favored over the reduction process. Interestingly, for bulky monoligated catalyst, Cycle B is energetically more favored over generally accepted Cycle A, in which the silylation channel is slightly disfavored in comparison to that of the reduction channel. Moreover, the inclusion of base in this channel allows the silylated product become dominant. These findings offer a good explanation for the complex experimental observations. Designing a reaction process that allows the oxidative addition of palladium(0) complex to aryl iodide to occur prior to that with hydrosilane is thus suggested to improve the reactivity and chemoselectivity for the silylated product by encouraging the catalytic cycle to proceed through Cycles B (monoligated Pd⁰ catalyst) or C (biligated Pd⁰ catalyst), instead of Cycle A.     

Diphenylphosphinite ionic liquid (IL-OPPh2): A solvent and ligand for palladium-catalyzed silylation and dehalogenation reaction of aryl halides with triethylsilane

The use of an imidazolium-based phosphinite ionic liquid (IL-OPPh₂) as both solvent and ligand for Pd offers an efficient catalytic system for silylation of aryl iodides, bromides and also chlorides by triethylsilane in the presence of Cs₂CO₃. In the absence of base, this system is also performed for catalytic dehalogenation of aryl halides. The ionic liquid containing its corresponding Pd(0) complex can be easily recovered and reused in several runs without losing its efficiency.     

Facile Synthesis of Soluble Poly(aryl alkyl ketone)s and a Simple Route Toward Conjugated Polymers

A new route for the synthesis of soluble poly(aryl alkyl ketone)s was developed employing the cross‐coupling reaction of an aryl dihalide and a diketone in the presence of a palladium complex and a sterically bulky phosphane. The solubility of the polymer can be controlled via the α‐substituent next to the carbonyl group. The polyketone can be converted easily to a conjugated polymer upon treatment with a silylation agent.     

Zirconocene-Catalyzed Silylation of Alkenes with Chlorosilanes

Vinylsilanes and/or allylsilanes are formed upon silylation of terminal alkenes with R₃^′SiCl in the presence of a Grignard reagent and a catalytic amount of [Cp₂ZrCl₂] [Eq. (a)]. The reaction also proceeds under mild conditions when silylsulfides (X=SPh), silylselenides (X=SePh), and silyltellurides (X=TePh) are used in place of chlorosilanes (X=Cl). R″=alkyl, aryl, alkylsilyl; R′=Me, Et, nPr; R=CH₂R″, aryl, H.     

Efficient synthesis of new 1-alkyl(aryl)-5-(3,3,3-trihalo-2-oxopropylidene)-1H-pyrrol-2(5H)-ones

The synthesis of 1-alkyl(aryl)-5-(3,3,3-trihalo-2-oxopropylidene)-1H-pyrrol-2(5H)-ones 5, 6a-d from 1-alkyl(aryl)-4-bromo-5-(3,3,3-trihalo-2-oxopropylidene)-1H-pyrrolidin-2-ones 3, 4a-d is reported. The 1-alkyl(aryl)-4-bromo-5-(3,3,3-trihalo-2-oxopropylidene)-1H-pyrrolidin-2-ones 3, 4a-d were obtained from regiospecific bromination of 1-alkyl(aryl)-5-(3,3,3-trihalo-2-oxopropylidene)-1H-pyrrolidin-2-ones 1, 2a-d with molecular bromine. The NMR and X-ray diffraction data showed that 1-alkyl(aryl)-5-(3,3,3-trihalo-2-oxopropylidene)-1H-pyrrolidin-2-ones were brominated at 4-position in the pyrrolidin-2-one ring.     

In-tube silylation in combination with thermal desorption gas chromatography-mass spectrometry for the determination of hydroxy polycyclic aromatic hydrocarbons in water

For the determination of hydroxy polycyclic aromatic hydrocarbons (OH-PAHs), a simple and sensitive method based on the silylation of OH-PAHs using N,O-bis(trimethylsilyl)trifluoro acetamide (BSTFA) in combination with thermal desorption gas chromatography-mass spectrometry (TD-GC-MS) is described. This method was performed by way of direct silylation in a TD unit (in-tube silylation) coupled to a GC inlet. Both a good detection limit (4.1-1200 pg L⁻¹, S/N = 3) and higher precision (relative standard deviation < 4% on average) were achieved for 21 OH-PAHs studied using the full scan mode (m/z = 40-550). These good results were due to the highly efficient derivatization of the OH-PAHs, which was attributed to not only the moisture-free environment and programmable heating in the TD tube for the in-tube silylation, but also to the constant vapor generation of BSTFA using a capillary introduction method. Although recoveries of 21 OH-PAHs from the spiked 3% NaCl solution ranged between 9 and 304%, those of 11 OH-PAHs fell between 70 and 130% (R.S.D. < 11%). Thus, the present method was applied to a seawater sample collected from an industrial port, and nine OH-PAHs including 1- and 2-OH-fluorenone and 1,8- and 2,6-OH-anthraquinone were determined at concentrations of 0.49-5.8 ng L⁻¹. Along with these OH-PAHs, significant amounts of several long chain fatty acids (C₁₂, C₁₆, C₁₈, C₂₀ and C₂₂) and bisphenol A were also identified in the seawater sample using reference data in a library of mass spectra (match factor: >80%).     

Über die Si3-N-bindung: XXXV. Darstellung von N-β-halogenäthyl-N,N-bis(trimethylsilyl)aminen

N-β-Haloethyl-N,N-bis(trimethylsilyl)amines, which can be used for the introduction of aminoethyl groups into organic or organosilicon compounds, are prepared in good yields from N-trimethylsilylaziridine and trimethylhalosilanes. This reaction is spontaneous with trimethylbromo- and -iodosilane, whereas it is necessary to run the reactions with trimethylchlorosilane in the presence of dipolar aprotic solvents and at higher temperatures.N-β-Bromoethyl-N,N-bis(trimethylsilyl)amine (II) is also obtained by silylation of N-β-bromoethylamine hydrobromide with trimethylsilyldiethylamine or with N-trimethylsilyl-N-methyl acetamide. Furthermore N-β-iodoethyl-N,N- bis(trimethylsilyl)amine is prepared by the reaction of II with MgI₂ or of aziridine and N-trimethylsilylaziridine respectively, with trimethylchlorosilane and MgI₂.From the silylation of N-β-bromoethylamine hydrobromide with trimethylsilyldiethylamine N,N-bis(trimethylsilyl)-N′,N′-diethylethylenediamine is isolated as a side product or, at higher temperatures, as the main product.     

A novel synthesis of 4,5-diaryl-6-arylamino-2,3-benzo-1,3a,6a-triazapentalenes

Treatment of N-alkyl- and N-aryl-imines of 2,3-diaryl- and 2-alkyl-3-aryl-3-(benzotriazol-1-yl)propenals with trifluoroacetic anhydride in THF at room temperature gave 5-alkyl-4-aryl-6-[N-alkyl (and aryl)-N-trifluoroacetyl]amino-2,3-benzo-1,3a,6a-triazapentalenes in moderate to good yields. On heating triazapentalenes having R²=aryl in MeOH at reflux, detrifluoroacetylation of triazapentalene occurred to give title compounds in good yields. However, the same treatment of triazapentalenes having R²=alkyl did not give the corresponding detrifluoroacetylation product. The title compounds and 5-alkyl-4-aryl-6-(N-alkyl-N-trifluoroacetyl)amino-2,3-benzo-1,3a,6a-triazapentalenes were found to be good precursors for the synthesis of 1-(o-aminophenyl)-3-arylamino-4-alkyl (and aryl)-5-arylpyrazoles and 1-(o-aminophenyl)-3-(N-alkyl-N-trifluoroacetyl)amino-4-alkyl (and aryl)-5-arylpyrazoles, respectively.     

Synthesis and antifungal property of N-(aryl) and quaternary N-(aryl) chitosan derivatives against Botrytis cinerea

A series of N-(aryl) and their quaternary N-(aryl) chitosan derivatives were synthesized and evaluated for their antifungal activity against crop-threatening fungus Botrytis cinerea. Schiff bases were firstly synthesized by the reaction of chitosan with cinnamaldehyde, cuminaldehyde and 4-dimethylaminobenzaldehyde followed by reduction with sodium borohydride to form N-(aryl) chitosans. Quaternary N-(aryl) chitosans were then obtained by reaction of N-(aryl) chitosan compounds with ethyl iodide. The chemical structures were characterized by ¹H-NMR, FT-IR and UV spectroscopic techniques. The antifungal activity was evaluated in vitro against B. cinerea by mycelial growth inhibition method and in vivo by application of compounds to tomato plants prior to inoculation with fungal spores. In an in vitro experiment, all quaternized chitosans were more active than N-(aryl) chitosan derivatives and N,N,N-(diethylcinnamyl) chitosan (QC1) was the most potent (EC₅₀ = 1,147 mg/L) against mecelia however, N,N,N-(diethyl-p-dimethylaminobenzyl) chitosan (QC3) was the most potent (EC₅₀ = 334 mg/L) against spores. In an in vivo study, no disease incidence (0.0 %) was observed with QC1 and QC3 at 1,000 mg/L. Spray liquid chitosan enhanced total phenolics and guaiacol peroxidase in inoculated leaves.     

Thioethers as Dichotomous Electrophiles for Site-Selective Silylation via C−S Bond Cleavage

The development of aryl alkyl sulfides as dichotomous electrophiles for site-selective silylation via C−S bond cleavage has been achieved. Iron-catalyzed selective cleavage of C(aryl)−S bonds can occur in the presence of β-diketimine ligands, and the cleavage of C(alkyl)−S bonds can be achieved by t-BuONa without the use of transition metals, resulting in the corresponding silylated products in moderate to excellent yields. Mechanistic studies suggest that Fe−Si species may undergo metathesis reactions during the cleavage of C(aryl)−S bonds, while silyl radicals are involved during the cleavage of C(alkyl)−S bonds.     

An efficient synthesis of α-aryl β-(N-tosyl)amino phosphonate derivatives from α-diazophosphonate

The α-diazophosphonate was added to aryl (N-tosyl)imine to give β-aryl β-(N-tosyl)amino α-diazophosphonates, which were further subjected to TsOH-catalyzed diazo decomposition to yield α-aryl β-(N-tosyl)enaminophosphonates through 1,2 aryl migration. The α-aryl β-(N-tosyl)enamino phosphonates were hydrogenated to give α-aryl β-(N-tosyl)amino phosphonates.     

Towards synthesis of kavalactone derivatives

Kavalactone derivatives were synthesized using a Heck reaction of the 4-methoxy-6-vinyl-5,6-dihydropyran-2-one with aryl iodides. The Suzuki-Miyaura reaction of an aryl boronic acid and (Z)-4-methoxy-6-(2-iodovinyl)-5,6-dihydropyran-2-one has also been successfully used to produce both Z and E isomers of lactones.     

Formation of chiral aryl ethers from enantiopure amine or alcohol substrates

Three methods for the preparation of chiral aryl ethers are demonstrated. N,N-Disulfonylimide derivatives are used in the stereoselective formation of aryl ethers from chiral amines. Nucleophilic attack of aryloxide anions on the cyclic N,N-disulfonylimide derivative of (S)-1-phenylethylamine afforded the (R)-1-phenylethyl phenyl and 2-naphthyl ethers with 83–87 and 70–79% inversion of configuration, respectively. The results are compared with results from alternative methods for the preparation of homochiral aryl ethers from chiral alcohols with complete retention and inversion of configuration, respectively.     

Hydrazine derivatives in the synthesis of linear and heterocyclic compounds

N-Siloxycarbonylation, transamination, carboxylation, silylation, and condensation of N,N-dimethylhydrazine, 1-methyl-1-[2-(1-methylhydrazino)ethyl]hydrazine, N-methyl-2-(1-methylhydrazino)ethanamine, and some their trimethylsilyl derivatives resulted in the formation of previously unknown linear and heterocyclic compounds.     

Synthesis of carbazoles by dehydro Diels-Alder reactions of ynamides

A new approach to carbazoles and benzannulated carbazoles by means of intramolecular dehydro Diels-Alder of ynamides is reported. N-(o-Ethynyl)aryl ynamides and N-(o-ethynyl) arylynamides were prepared in a few steps starting from o-iodoaniline. Thermal cycloaddition of N-(o-ethynyl)aryl ynamides and N-(o-ethynyl) arylynamides affords carbazoles and benzannulated and heteroannulated carbazoles in moderate-to-good yields.     

Synthese und reaktionen von 1-germcyclohexa-2,4-dienen und 1-germacyclohexa-2,4-dien-eisentricarbonylen

1,1-Diakyl(aryl)4-alkyl(aryl)-4-methoxy-1-germacyclohexa-2,5-dienes undergo ether cleavage with sodium in n-pentane or liquid ammonia. Hydrolysis of the resulting sodium salts yields the 1,1-dialkyl(aryl)-4-alkyl(aryl)-1-germacyclohexa-2,4-dienes. Reduction of 1-chloro-4-methoxy-1-germacyclohexa-2,5-dienes with LiAlH₄ can be directed to give the 1H-1-germacyclohexa-2,4-dienes with ether cleavage.The 1H-1-germacyclohexadienes are chlorinated by PCl₅ and brominated by N-bromosuccinimide to the 1-chloro- or 1-bromo-1-germacyclohexa-2,4-dienes, respectively. 1,1-Diethyl-4-phenyl-4-methoxy-1-germacyclohexa-2,5-diene reacts with PCl₃ with ether cleavage and formation of the 6-chloro-1-germacyclohexa-2,4-diene. Ether cleavage is also possible with BCl₃, the 1-phenyl-1-chloro-4R-4-methoxy-1-germacyclohexa-2,5-dienes are transformed into the 1-phenyl-1,6-dichloro-4R-1-germacyclohexa-2,4-dienes.The Fe(CO)₃ complexes of 1,1-dialkyl(aryl)-1-germacyclohexa-2,4-dienes were synthesized.