Synthesis of 1,1,4,4-tetrabromo-2-butenes and related compounds via desilylation-bromination of silylated 1,3-butadiene derivatives

The combination of zirconocene-mediated coupling of silylated alkynes with a protonation-desilylation or bromination-desilylation process afforded otherwise unavailable butadiene derivatives. When (E,E)-2,3-dialkyl-1,4-bis(trimethylsilyl)-1,3-butadienes were treated with 3 equiv of Br(2) in CH(2)Cl(2), (E)-2,3-dialkyl-1,1,4,4-tetrabromo-2-butenes were obtained in excellent yields with perfect stereoselectivity.     

Catalytically active, recyclable polymeric titanocene disks: a batch-flow reactor

Dichlorotitanocene bound within porous polystyrene disks catalyzes the coupling of vinylmagnesium chloride and chlorosilanes to form 1,4-bis(silyl)-2-butenes. A simple batch-flow reactor permits catalyst reuse by repeated addition of fresh reagents and decantation of products.     

1,4-Dialkynylbutatrienes: synthesis, stability, and perspectives in the chemistry of carbo-benzenes

The π-electron-rich C(8)-conjugated sequence of 1,4-dialkynylbutatrienes is identified as a fragile and fascinating motif occurring in carbo-benzene derivatives, and in Diederich's 1,4-bis(arylethynyl)- or 1,4-bis(triisopropylsilylethynyl)butatriene "capped" representatives, in particular, in tetraalkynylbutatriene. The family of symmetrical 1,4-dialkynylbutatrienes (E-C≡C)RC=C=C=CR(C≡C-E) is extended to functional caps (E=H, CH(3), C≡CPh, CPh=CHBr, or CPh=CBr(2)) with non-alkynyl substituents at the sp(2) vertices (R=Ph or CF(3)). The targets were selected for their potential in appealing retrosynthetic routes to carbo-benzenes, in which the aromatic C(18) macrocycle would be directly generated by sequential metathesis or reductive coupling processes. The functional 1,4-dialkynylbutrienes were synthesized by either classical methods used for the preparation of generic butatrienes (R'Li/CuX-mediated reductive coupling of gem-dihaloenynes or SnCl(2)/HCl-mediated reduction of 3,6-dioxy-octa-1,4,7-triyne precursors). Their spectroscopic and electrochemical properties are compared and analyzed on the basis of the relative extent of total conjugation.     

Production of propylene from an unconventional metathesis of ethylene and 2-pentene over Re2O7/SiO2-Al2O3 catalysts

An unconventional metathesis of ethylene and 2-pentene over Re2O7/SiO2-Al2O3 catalysts has been studied as an alternative route for the production of propylene. Complete conversion of 2-pentene and propylene yield as high as 88 wt% were obtained under mild reaction conditions at 35°C and atmospheric pressure. Unlike the conventional metathesis of ethylene and 2-butenes in which isomerization is a competing side reaction, the isomerization of 1-butene product from the unconventional metathesis of ethylene and 2-pentene to 2-butenes can further react with excess ethylene in the feed, resulting in additional increase in propylene yield. The secondary metathesis reaction was found to be favored under ethylene/2-pentene (E/2P) molar ratio 3 and gas hourly space velocity (GHSV) 1000 h-1 at the reaction temperature of 35°C. No catalyst deactivation was observed during the 455 min time-on-stream under the selected reaction conditions.     

Role of support nature （γ-Al2O3 and SiO2-Al2O3） on the performances of rhenium oxide catalysts in the metathesis of ethylene and 2-pentene

The metathesis of ethylene and 2-pentene was studied as an alternative route for propylene production over Re2O7/γ-Al2O3 and Re2O7/SiO2-Al2O3 catalysts. Both NH3 temperature-programmed desorption (NH3-TPD) and H2 temperature-programmed reduction (H2-TPR) results showed that Re2O7/SiO2-Al2O3 exhibited stronger acidity and weaker metal-support interaction than Re2O7/γ-Al2O3. At 35 60℃, isomerization free metathesis was observed only over Re2O7/γ-Al2O3, suggesting that the formation of metal-carbene metathesis active sites required only weak acidity. Our results suggest that on the Re2O7/SiO2-Al2O3, hydrido-rhenium species ([Re]-H) were formed in addition to the metathesis active sites, resulting in the isomerization of the initial 1-butene product into 2-butenes. A subsequent secondary metathesis reaction between these 2-butenes and the excess ethylene could explain the enhanced yields of propylene observed. The results demonstrate the potential for high yield of propylene from alternative feedstocks.     

Preparation of cyclophanes by room-temperature ring-closing alkyne metathesis with imidazolin-2-iminato tungsten alkylidyne complexes

Room-temperature ring-closing alkyne metathesis of 1,2-, 1,3-, and 1,4-bis(3-pentynyloxymethyl)benzenes has been investigated in the presence of catalytic amounts of an imidazolin-2-iminato tungsten alkylidyne complex. The m- and p-diynes selectively form the respective [10]metacyclophane or [10.10]paracyclophane, respectively, whereas a mixture of monomeric and dimeric cycloalkynes is obtained in the case of the o-diyne. DFT calculations reveal that the different selectivities can be attributed to the relative thermodynamic stability of the emerging cyclophanes.     

Metathesis reactions of allylsilanes containing bulky aromatic substituents

Bulky substituents, such as -naphthyl and ferrocenyl groups, do not inhibit the metathesis of allylsilanes on a Re₂O₇/Al₂O₃-SnBu₄, catalyst system. Metathesis represents a preparative synthetic method for the synthesis of 1,4-bis(-napthyl-dimethylsilyl)- and 1,4-bis(ferrocenyldimethylsilyl)but-2-enes.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1207–1209, May, 1991.     

A stereoselective synthesis of a spiro-bridged bis(α-amino acid) derivative based on Ru(II)-catalysed RCM reactions

Methodology for a stereoselective synthesis of a member of a novel family of spiro-bridged bis(α-amino acid) derivatives is described. The key step in the construction is a spirane annulation reaction effected by a Ru(II)-catalysed ring-closing metathesis (RCM) reaction of an appropriately substituted tetraene. The latter became available after stereocontrolled allylations of 3,3-bis[2-((2S,5R)-5-isopropyl-3,6-dimethoxy-2,5-dihydropyrazin-2-yl)ethyl]-1,4-pentadiene, which was prepared in several reaction steps from (2R)-2,5-dihydro-2-isopropyl-3,6-dimethoxypyrazine as a chiral starting material.     

Synthesis of soluble all-trans oligomers of 2,5-diheptyloxy-p-phenylenevinylene via olefin metathesis

In this paper we report on the synthesis of all-trans oligomers of 2,5-diheptyloxy-p-phenylenevinylene (2,5-diheptyloxy-PV) via olefin metathesis condensation of 2,5-diheptyloxy-1,4-divinylbenzene

1 The correct IUPAC name is 1,4-bis(heptyloxy)-2,5-divinylbenzene. The name 2,5-diheptyloxy-1,4-divinylbenzene is used in order to underline the structural similarity to 2,5-diheptyloxy-p-phenylenevinylene oligomers.

(2,5-diheptyloxy-DVB). The preparation of the monomer is also described. The Schrock type molybdenum alkylidene complex Mo(NPhMe₂)(CHCMe₂Ph)(OCMe[CF₃]₂)₂ was used as metathesis catalyst. The oligomer product obtained was characterized by means of ¹H NMR, IR and UV/Vis spectroscopy and gel permeation chromatography.     

(E)- and (Z)-1-benzenesulfonyl-4-trimethylsilyl-2-butenes as (E)-1-(1,3-butadienyl) synthons

(E)- and (Z)-1-benzenesulfonyl-4-trimethylsilyl-2-butenes (E/Z=9), prepared from 4-trimethylsilyl-1-buten-3-ol, $\text{n}$-butyllithium and benzenesulfenyl chloride and oxidation of the intermediate (E)- and (Z)-1-benzenesulfinyl-4-trimethylsilyl-2-butenes with hydrogen peroxide, react with $\text{n}$-butyllithium and then primary halides to give 4-benzenesulfonyl-1-trimethylsilyl-2-alkenes which are rapidly 1,4-debenzenesulfonyltrimethylsilated to (E)-1,3-alkadienes by tetra-$\text{n}$-butylammonium fluoride at O°C.     

A New Protocol to Generate Catalytically Active Species of Group 4–6 Metals by Organosilicon-Based Salt-Free Reductants

Herein, we provide a new protocol to reduce various transition-metal complexes by using organosilicon compounds in a salt-free fashion with the great advantage of generating pure low-valent metal species and metallic(0) nanoparticles, in sharp contrast to reductant-derived salt contaminants obtained by reduction with metal reductants. The organosilicon derivatives 1,4-bis(trimethylsilyl)-2,5-cyclohexadiene ( 1 a ), 1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene ( 1 b ), 1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene ( 2 a ), 2,5-dimethyl-1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene ( 2 b ), 2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene ( 2 c ), and 1,1′-bis(trimethylsilyl)-1H,1′H-4,4′-bipyridinylidene ( 3 ) all served as versatile reductants for early transition-metal complexes and produced only easy-to-remove organic compounds, such as trimethylsilylated compounds and the corresponding aromatics, for example, benzene, toluene, pyrazine, and 4,4′-bipyridyl, as the byproducts. The high solubility of the reductants in organic solvents enabled us to monitor the catalytic reactions directly and to detect any catalytically active species so that we could elucidate the reaction mechanism.     

Reactions of 1,4-bis(tetrazole)benzenes: formation of long chain alkyl halides

The reactions of 1,4-bis[2-(tributylstannyl)tetrazol-5-yl]benzene with α,ω-dibromoalkanes were carried out in order to synthesise pendant alkyl halide derivatives of the parent bis-tetrazole. This led to the formation of several alkyl halide derivatives, substituted variously at N1 or N2 on the tetrazole ring. The crystal structures of 1,4-bis[(2-(4-bromobutyl)tetrazol-5-yl)]benzene (2-N,2-N′), 1,4-bis[(2-(4-bromobutyl)tetrazol-5-yl)]benzene (1-N,2-N′) and 1,4-bis[(2-(8-bromooctyl)tetrazol-5-yl)]benzene (2-N,2-N′) are reported. Further discussion involves the structure of 1,4-bis[2-(6-bromohexyl)-2H-tetrazol-5-yl]benzene (2-N,2-N′) previously reported.     

Isomerization and ring-closing metathesis for the synthesis of 6-, 7- and 8-membered benzo- and pyrido-fused N,N-, N,O- and N,S-heterocycles

An isomerization-ring-closing metathesis (RCM) strategy afforded N-substituted 4H-1,4-benzoxazines from the protected N-allyl-2-(allyloxy)anilines. In addition, RCM was used to synthesize the N-substituted, 8-membered benzo-fused heterocycles from the respective diallyl compounds: 1,2,5,6-tetrahydro-1,6-benzodiazocine, 5,6-dihydro-2H-1,6-benzoxazocine, 5,6,9,10-tetrahydropyrido[2,3-b][1,4]diazocine and 5,6-dihydro-2H-1,6-benzothiazocine 1,1-dioxide. The isomerization-RCM approach also afforded the 7-membered ring system, 2,5-dihydro-1,5-benzothiazepine 1,1-dioxide, from the protected N-allyl-2-(allylsulfonyl)aniline. Furthermore, the structure of 1,6-bis[(4-methylphenyl)sulfonyl]-1,2,5,6-tetrahydro-1,6-benzodiazocine was confirmed by a single crystal X-ray determination.     

Photochemical reaction of silyl-substituted 1,4-disila(dewar-benzene) with isocyanide and phenylacetylene

The irradiation of silyl-substituted 1,4-disila(Dewar-benzene) 1 with light of wavelength λ > 320 nm in the presence of 2,6-dimethylphenyl-isocyanide or phenylacetylene produced 1,4-bis(di-tert-butylmethylsilyl)-2,3,5,6-tetraethyl-7-(2,6-dime-thylphenylimino)-1,4-disilabicyclo[2.2.1]hepta-2,5-diene 5 or 1,4-bis(di-tert-butylmethylsilyl)-2,3,5,6-tetraethyl-1-(2-phenylethynyl)-1,4-disilacyclohexa-2,5-diene 6 , respectively. The molecular structures of 5 and 6 were determined by spectroscopic data and X-ray crystallography. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:87–92, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20411     

Synthesis of a new polyfluorinated vinylogue of tetrathiafulvalene through 1,3-dipolar cycloaddition of ethyl beta-bromoperfluorodithiocrotonate with dimethyl acetylenedicarboxylate

The ethyl ester of beta-bromoperfluorodithiocrotonic acid reacts with dimethyl acetylenedicarboxylate to give 1,4-difluoro-2,3-bis(trifluoromethyl)-but-2-ene-1,4-diylidene-2,2'-bis(4',5'-dicarbomethoxy-1',3'-dithiole) (4), a new type of vinylogue of tetrathiafulvalene. The thermal transformations of this compound lead, depending on the temperature, to the formation of the cyclization products: 11,14-difluoro-2,3,8,9-tetra(carbomethoxy)-12,13-bis(trifluoromethyl)-1,4,7,10-tetrathiadispiro[4.0.4.4]tetradeca-2,8,11,13-tetraene (8) or 5,8-difluoro-6,7-bis(trifluoromethyl)-2,3-bis(carboxymethyl)-1,4-benzodithiine (11).     

Palladium-catalyzed asymmetric tandem allylic substitution using chiral 2-(phosphinophenyl)pyridine ligand

Palladium-catalyzed asymmetric tandem allylic substitution of (Z)-1,4-diacyloxy- and (Z)-1,4-bis(alkoxycarbonyloxy)-2-butene (2a-c) using 2-(phosphinophenyl)pyridine 1 as chiral ligand provided optically active six-membered 2-vinyl-1,4-diheterocyclic compounds with good to high enantioselectivity. For example, the reactions with catechol, 2-(benzylamino)phenol, or 1,2-bis(benzylamino)ethane as a nucleophile gave 2-vinyl-1,4-benzodioxane (71% ee), 4-benzyl-2-vinyl-1,4-benzoxazine (86% ee), and 1,4-dibenzyl-2-vinylpiperazine (86% ee), respectively.     

Electrochemical and spectral properties of thienylene-polyparaphenylenevinylene derivative stereoisomers

Four new compounds: 1,4-dimetoxy-2,5-bis[2-(tien-2-yl)ethenyl]benzene), 1,4-dietoxy-2,5-bis[2-(tien-2-yl)ethenyl]benzene), 1,4-isopropyloxy-2,5-bis[2-(tien-2-yl)ethenyl]benzene) and 1,4-dietoksy-2,5-bis[2-(5-methylthiophen-2-yl)ethenyl]benzene are synthesized. Three steroisomers ZZ, EZ and EE are isolated from the reaction mixture for the first two of them. Third compound is fully converted to the most stable EE form. Polymerization of all isomers leads to identical polymeric product. Mechanism of polymerization is recognized by using model molecule with methyl substituents blocking α-, α′-sites. All seven stereoisomers have photoluminescent properties. Detailed spectral and electrochemical studies reveal isomerization phenomena during oxidation or at light exposure. Published in Russian in Elektrekhimiya, 2006, Vol. 42, No. 12, pp. 1401–1408. Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes.” October 18–22, 2005, Moscow. The text was submitted by the authors in English.     

Simons electrochemical fluorination of substituted homopiperazines(hexahydro-1,4-diazepines) and piperazines

Simons electrochemical fluorination (ECF) of 1,4-dimethyl-1,4-homopiperazine, methyl 4-ethylhomopiperazin-1-ylacetate and 1,4-bis(methoxycarbonylmethyl)-1,4-homopiperazine was studied. For comparison, ECF of three piperazines with a N-(methoxycarbonylmethyl) group(s) was also studied. ECF of 1,4-dimethyl-1,4-homopiperazine gave a low yield of corresponding perfluoro(1,4-dimethyl-1,4-homopiperazine) together with perfluoro(2,6-diaza-2,6-dimethylheptane) as the major product. Corresponding perfluoro(homopiperazines) with mono- and/or di-(fluorocarbonyldifluoromethyl) groups [CF₂C(O)F] at the 1- and/or 4-position were formed in low yields from methyl 4-ethylhomopiperazin-1-ylacetate and 1,4-bis(methoxycarbonylmethyl)-1,4-homopiperazine, respectively. These new seven-membered perfluoro(1,4-dialkyl-1,4-homopiperazines) were accompanied by the formation of mono- and/or di-basic linear perfluoroacid fluorides resulting from the CC bond scission at the 2- and 3-positions of the ring. From mono- and/or di-N-(methoxycarbonylmethyl)-substituted piperazines, corresponding perfluoropeperazines having the acid fluoride group(s) were formed in low yields.     

Direct evidence of crosslinks by metathesis degradation

The degradation of unsaturated polymers by olefin metathesis has already been applied to the investigation of crosslink structures. In the present paper, crosslinks in poly(butadiene-alt-propene), obtained by partial bromination with N-bromosuccinimide and reaction with 1,4-bis(bromomagnesium)butane, were investigated by this method. Metathesis degradation was carried out with (E)-4-octene using the catalyst WCl₆-Sn(CH₃)₄. The low-molecular-weight products were identified by combination of gas chromatography (GC) and mass spectrometry (MS).     

Synthesis of pyranonaphthoquinone antibiotics involving the ring closing metathesis of a vinyl ether

The synthesis of two antibiotic pyranonaphthoquinones was performed by a straightforward synthetic route utilizing ring closing metathesis. Vinylation of 3-(1-propenyl)-2-hydroxymethyl-1,4-dimethoxynaphthalene under iridium catalysis and subsequent ring closing metathesis of 3-(1-propenyl)-2-vinyloxymethyl-1,4-dimethoxynaphthalene with Grubbs' catalyst paved the way to the natural antibiotics pentalongin and psychorubrin.