Unsymmetrically substituted N-heterocyclic phosphenium ions

Reduction of an unsymmetrically substituted α-diimine followed by condensation with PCl₃ yielded a P-chloro-N-aryl-N′-alkyl diazaphospholene which was further converted into an unsymmetrical diazaphospholium triflate by reaction with trimethylsilyl triflate. Reaction of tetramers of N-H- or N-alkyl-benzo-1,3,2-diazaphospholes with methyl triflate or triflic acid led in one step to triflate salts of unsymmetrically substituted benzo-1,3,2-diazaphospholium cations. Determination of the crystal structures of two of these derivatives by single-crystal X-ray diffraction studies revealed that individual cations and anions in the crystal lattice interact via specific electrostatic, π-stacking, or van-der-Waals type interactions to form supramolecular assemblies. Thermoanalytical measurements disclosed that benzo-diazaphospholium triflates with medium length alkyl chains melt below 100 °C and exhibit a strong tendency to form supercooled liquids.     

Zur synthese funktionel substituierter polysilane mittels trifluormethansulfonsäure

The cleavage of silicon phenyl bonds in phenylmethylpolysilane by CF₃SO₃H leads to triflate derivatives of polysilanes. The polymers react with lithium derivatives or acidic element hydrogen compounds under formation of numerous substituted polysilanes.     

Beiträge zur Chemie der Silicium–Stickstoff-Verbindungen. CXXXII. Derivate des 1,2,3-Trisila-3,5-diaza-cyclopentan-Ringsystems

Chemistry of Silicon-Nitrogen Compounds. CXXXII. Derivatives of the 1,2,4-Trisila-3,5-diaza-cyclopentane Ring System The derivatives B1 – B6 of the title ring system could be prepared for the first time by reaction of 1,2-bis(alkylamino)disilanes ( A 1, A 2) with dihalosilanes (Scheme 1). They were transformed by additional reactions with methanol or amines into B7 – B9 . The Cl₂Si derivative B2 is characterized by an unusual stability against aqueous solutions.     

Aminosubstituted disilanes: Synthesis by unsymmetrical and symmetrical reductive coupling

The reductive coupling of chlorotris(diorganylamino)silanes 1 with chlorotrimethylsilane by the action oflithium in THF provides for steric reasons, an easy access to unsymmetrical aminosubstituted disilanes (R₂N)₃Si-SiMe₃ 3. Similarly, cross-coupling to give pentakis(diethylamino)disilane 4 is observed between 1a and bis(diethylamino)chloro-hydridosilane 2a on treatment with lithium. In reactions of the less bulky bis(diorganylamino)chlorohy-dridosilanes 2 with ClSiMe₃ and Li, however, thesymmetrical coupling is preferred and affords SiH-functional substituted (R₂N)₃₂HSi-SiH(NR₂)₂ 5. Aminosubstituted disilanes 3–5 are useful starting materials for modification of disilanes or syntheses ofsilicon heterocycles via generation and trapping of aminosilylenes, as exemplified by diethylaminosilacyclopent-3-ene 6a. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:311–316, 1998     

Convenient approach to novel functional substituted and branched poly(silylenemethylenes)

Novel poly(silylenemethylenes) have been prepared by the ring-opening polymerization of 1,3-disilacyclobutanes followed by a protodesilylation reaction with triflic acid. The silicon–aryl bond cleavage could be controlled by using different leaving groups, for instance phenyl- and para-anisyl substituents. The reactions of the triflate derivatives with organomagnesium compounds, LiAlH₄, amines, or alcohols gave functional substituted poly(silylenemethylenes). Hydrosilylation reactions or reductive coupling with potassium–graphite led to organosilicon network–polymers, which may serve as suitable precursors for silicon carbide and Si/C/N-based materials. The structures of the polymers were identified by NMR spectroscopy (²⁹Si, ¹³C, ¹H). © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 725–735, 1998     

Synthesis,functionalization and crosslinking reactions of poly(silylenemethylene)s

Novel poly(silylenemethylene)s have been prepared by the ring‐opening polymerization of 1,3‐disilacyclobutanes followed by a protodesilylation reaction with triflic acid. The silicon–aryl bond cleavage could be controlled by using different leaving groups, for instance phenyl‐ and para‐anisyl substituents. The reactions of the triflate derivatives with organomagnesium compounds, LiAlH₄, amines or alcohols gave functional substituted poly(silylenemethylene)s. Hydrosilylation reactions or reductive coupling with potassium–graphite led to organosilicon network‐polymers, which may serve as suitable precursors for silicon carbide and Si/C/N‐based materials. The structures of the polymers were identified by nuclear magnetic resonance spectroscopy (²⁹Si, ¹³C, ¹H). Copyright © 1999 John Wiley & Sons, Ltd.     

Synthesis and functionalization of Poly[5,5′‐(silylene)‐2,2′‐dithienylene]s using silyl triflate intermediates†

Treatment of 5,5′‐dilithio‐2,2′‐dithiophene with (dimethylamino)methylsily bis(triflate)‐ or α, ω‐bis(triflate)‐substituted trisilanes gave poly[5,5′‐(silylene)‐2,2′‐dithienylene]s in high yields. The amino–silyl bond was cleaved selectively by triflic acid, leading to triflate‐substituted derivatives. Conversion of these compounds with nucleophiles gave other functionalized polymers. Platinum‐catalyzed hydrosilylation reactions between silicon–vinyl and silicon–hydrogen derivatives result in polymer networks which may serve as interesting preceramic materials. The structures of the polymers were proven by NMR spectroscopy (²⁹Si, ¹³C, ¹H). Results of thermal gravimetric analysis (TGA), UV spectrometry and conductivity measurements are given. Copyright © 1999 John Wiley & Sons, Ltd.     

Reaction paths of 1,3-oxazolinium saltz with stabilized carbanions

Reaction of stabilized carbanions with 3-methyl-2-phenyl-1,3-oxazolinium triflate occurs at both C₅ and C₂ sites with a regioselectivity depending partially on steric effects. The reaction at C₂ site can result in the formation of 1,4-oxazepin derivatives.     

Synthesis of thiophene derivatives via palladium-catalyzed coupling reactions

Thiophene derivatives with multiple substitutions are prepared from vinylidene bromide, which is synthesized by the reaction of thiophene-2-carboxaldehyde with carbon tetrabromide in the presence of PPh₃, as a core molecule through several coupling reactions such as Suzuki-Miyaura coupling and palladium-catalyzed CH arylation. The reactions with a wide variety of organic halides lead to a series of substituted thiophene derivatives in moderate to good yields.     

β‐Selective Glycosylation by Using O‐Aryl‐Protected Glycosyl Donors

New glycosyl donors have been developed that contained several para‐substituted O‐aryl protecting groups and their stereoselectivity for the glycosylation reaction was evaluated. A highly β‐selective glycosylation reaction was achieved by using thioglycosides that were protected by 4‐nitrophenyl (NP) groups, which were introduced by using the corresponding diaryliodonium triflate. Analysis of the stereoselectivities of several glycosyl donors indicated that the β‐glycosides were obtained through an S_N2‐type displacement from the corresponding α‐glycosyl triflate. The NP group could be removed by reduction of the nitro group and acylation, followed by oxidation with ceric ammonium nitrate (CAN).     

Disilane Cleavage with Selected Alkali and Alkaline Earth Metal Salts

The industry-scale production of methylchloromonosilanes in the Müller–Rochow Direct Process is accompanied by the formation of a residue, the direct process residue (DPR), comprised of disilanes Me_nSi₂Cl_6-n (n=1–6). Great research efforts have been devoted to the recycling of these disilanes into monosilanes to allow reintroduction into the siloxane production chain. In this work, disilane cleavage by using alkali and alkaline earth metal salts is reported. The reaction with metal hydrides, in particular lithium hydride (LiH), leads to efficient reduction of chlorine containing disilanes but also induces disproportionation into mono- and oligosilanes. Alkali and alkaline earth chlorides, formed in the course of the reduction, specifically induce disproportionation of highly chlorinated disilanes, whereas highly methylated disilanes (n>3) remain unreacted. Nearly quantitative DPR conversion into monosilanes was achieved by using concentrated HCl/ether solutions in the presence of lithium chloride.     

Ultrasound-assisted rapid synthesis of <Emphasis Type="Italic">β</Emphasis>-aminoketones with direct-type catalytic Mannich reaction using bismuth(III) triflate in aqueous media at room temperature

An innovative, powerful, efficient and relatively rapid method was developed to synthesise various β-aminoketone derivatives from cyclohexanone, substituted aromatic amines and aromatic or hetero-aromatic aldehydes via ultrasound-assisted direct-type catalytic Mannich reaction using bismuth(III) triflate in water. Good yields of the desired β-aminoketones were obtained at room temperature by ultrasound-assisted reaction within 1–2 h. The major advantages of the proposed method are undemanding conditions, easy operation, low toxicity, shorter reaction time, anti selectivity and higher yields in comparison with conventional methods.     

Synthesis of di- and trisilanes with potentially chelating substituents

Silylenes 2 or 4, generated by thermolysis of cyclotrisilanes 1 and 3, were inserted into the SiCl or SiH bonds of monosilanes to yield a variety of disilanes, which can be further functionalized subsequently. In a few cases, trisilanes are accessible by the reaction of 1 with disilanes. The reaction of a metalated silane with a chlorosilane is an alternative method for the formation of SiSi bonds, which turned out to be especially useful for the synthesis of bulkily substituted disilanes. Some of the new dichlorodi- and trisilanes themselves serve as thermal precursors of silylenes 2 or 4, the extrusion of which can be catalyzed by 1 or 3 in certain cases.     

Do halogen and methyl substituents have electronic effects on the structures of simple disilanes? An experimental and theoretical study of the molecular structures of the series X3SiSiMe3 (X = H, F, Cl and Br)

The gas-phase molecular structures of a series of halogen-substituted disilanes [X₃SiSiMe₃ (X = H, F, Cl and Br)], 1,1,1-trimethyldisilane (H₃SiSiMe₃), 1,1,1-trifluoro-2,2,2-trimethyldisilane (F₃SiSiMe₃), 1,1,1-trichloro-2,2,2-trimethyldisilane (Cl₃SiSiMe₃) and 1,1,1-tribromo-2,2,2-trimethyldisilane (Br₃SiSiMe₃), have been determined in the gas phase by electron diffraction. Ab initio calculations at the HF and MP2 level were used to support the experimental investigation using the SARACEN method. All of the investigated structures were determined to adopt a staggered structure with C _3v symmetry. The effect of substitution on the Si–Si bond and the Si–Si–X bond angle was investigated and these results were compared to results obtained from a recent study of halogen-substituted disilanes [X₃SiSiXMe₂ (X = F, Cl, Br and I)] to consider the effect of the methyl groups on the substituted disilanes.     

Facile One‐Pot Synthesis of 2‐Aryl‐substituted Nitriles and 2‐Aryl‐3‐keto Nitriles via Benzyne Reaction

2‐Aryl‐substituted nitriles were prepared in good to excellent yields in a one‐pot reaction by the reaction of benzyne, generated using neutral conditions from (phenyl)[o‐(trimethylsilyl)‐phenyl]iodonium triflate, and 2‐lithionitriles. 3‐Keto nitriles substituted at the 2‐position were obtained in good yields when these reactions were trapped with acid chlorides. The mechanism of the benzyne reaction in terms of a N‐lithiobenzocyclobutanimine intermediate is discussed.     

Preparation of substituted network polysilanes by a disproportionation reaction of ethoxydisilane initiated by a small amount of organolithium reagents

Network methylethoxypolysilanes containing various substituents such as phenyl, butyl, phenylene, thiophene, and anthracene groups were prepared by a disproportionation reaction of 1,1,2,2-tetraethoxy-1,2-dimethyldisilane initiated by addition of a small amount of organolithium reagents that have the corresponding substituents. The reaction was considered to be catalyzed by lithium ethoxide, which was formed by the substitution reaction of the ethoxydisilane with the lithium reagents. Both the substituted and pristine disilanes participated in the disproportionation reaction to yield the network polysilanes. The amount of the substituents and the molecular weight of the polysilanes varied, depending on what and how much of the lithium reagent were used. The electrical conductivity of some polysilanes was measured, and polymers with thiophene or anthracene groups were found to show relatively higher conductivity of 10⁻⁴ Scm⁻¹ after iodine doping. © 1997 John Wiley & Sons, Inc.     

Reactions of Heteroaryl Substituted Propenones

Thienyl- and furylpropenones reacted with malonates, cyanoacetates, and malononitrile giving addition products which could be cyclized to heteroaryl substituted dihydropyranes, cyclohexanols, and piperidones. Heteroaryl substituted cyclopropyl ketones were prepared by reactions with Me₃SO⁺ I⁺, and by reaction with Lewis acids they were transformed into substituted dihydrobenzo[b]furanone or -thiophenone, or -hydroxy ketones. Cycloadditions with thiophene derivatives allowed the synthesis of substituted benzo[b]thiophene derivatives, but with poor yields. Structures and stereochemistry were established mainly by means of NMR spectroscopy.     

Stereoselective synthesis of chiral hydrocarbazoles via the catalytic Diels–Alder reaction of siloxyvinylindole and cyclic Z-olefin

The catalytic Diels–Alder reaction of siloxyvinylindole and cyclic Z-olefin derived from pyroglutamic acid gave optically active substituted hydrocarbazoles. The exo/endo selectivity of this reaction could be controlled by using an appropriate Lewis acid. Scandium triflate gave high exo-selectivity and copper triflate gave moderate endo-selectivity. Subsequent stereoselective alkylation of the cycloadduct led to the synthesis of highly substituted hydrocarbazoles with five continuous chiral centers including a quaternary carbon.     

Preparation of 3,4,5-substituted furan-2(5H)-ones using aluminum hydrogen sulfate as an efficient catalyst

Various derivatives of 3,4,5-substituted furan-2(5H)-ones have been readily prepared by using aluminum hydrogen sulfate [Al(HSO₄)₃] as an efficient catalyst in good yields and milder reaction conditions. The versatility of this protocol has been demonstrated with various substituted furan-2(5H)-ones.     

Infrarot- und Raman-Spektren einiger Bromdisilane und Ioddisilane

Infrared and Raman spectra of the disilanes X₃SiSiH₃, X₂HSiSiHX₂(X = Br, I) and IH₂SiSiH₂I and their deuterated derivatives are reported and assigned. The measured H/D isotope shifts are used for a normal coordinate analysis.