A new catalytic route to synthesis of silylgermylethynes

Silylgermylethynes known to be potential organometallic reagents and precursors of optoelectronic materials can be efficiently synthesized via a recently reported catalytic method called silylative coupling of alkynes with vinylsilicon compounds. The reaction of triethylethynylgermane with vinyltrisubstituted silanes catalyzed by [RuHCl(CO)(PR₃)_n] (where R = ⁱPr, Cy, Ph; n = 2-3) under optimal conditions selectively yields respective silylgermylethynes. Silylation of ethynylgermane with divinylsilicon derivatives such as siloxanes, silazanes, bis(silyl)benzene and bis(silyl)ethane gives monoethynylgermyl substituted vinyldisilicon products with high yields and selectivity, however, accompanied by traces of dialkynylgermyl derivatives. All catalytic results as well as those of stoichiometric study on the insertion of ethynylgermane into Ru-Si bond have permitted proposing mechanistic schemes of the reaction examined.     

A new method for the synthesis of cinnamonitriles by catalytic olefination

Catalytic olefination of hydrazones of aromatic aldehydes with dibromoacetonitrile affords cinnamonitriles.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 247–249, January, 2005.     

Study on the Regioselectivity of Rhodium-Catalyzed Ring Opening Reactions of C1-Substituted 7-Oxabenzonorbornadienes with Boronic Acids

An optimized condition for the rhodium-catalyzed ring-opening reaction of C₁-substituted oxabicyclic alkenes with aryl boronic acids was developed and the effect of aryl boronic acid as well as the effect of C₁ substitution on the oxabicyclic alkenes was studied. Aryl boronic acids carrying electron-donating substituents provided the ring-opened products in excellent yields regardless of the position, while electron-withdrawing substituents were more susceptible to steric interactions. Although two different regioisomers are possible, all the rhodium-catalyzed ring-opening reactions of C₁ substituted oxabicyclic alkenes studied with aryl boronic acids were found to be highly regioselective, giving single regioisomers in all cases.     

A straightforward method for the synthesis of unsymmetrically substituted 1,3-diynes

An efficient synthetic approach to a variety of unsymmetrically substituted conjugated diynes has been developed, starting from the readily available 1,4-bis(trimethylsilyl)-1,3-butadiyne, based upon the selective and sequential substitution of the trimethylsilyl groups with alkyl, aryl and vinyl groups.     

A new method for the synthesis of 5-amidinobarbiturates

The reactions of 5-[arylamino(methylthio)methylene]pyrimidine-2,4,6(1H,3H,5H)-triones with different aliphatic and aromatic amines were studied. A series of 5-amidinobarbiturates was synthesized. A new and preparatively convenient method for their synthesis appropriate for the use in the combinatorial chemistry was developed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1557–1563, August, 2007.     

A new mild method for the one-pot synthesis of pyridines

Polysubstituted pyridines are prepared in good yield and with total regiocontrol by the one-pot reaction of an alkynone, 1,3-dicarbonyl compound and ammonium acetate in alcoholic solvents. This new three-component heteroannulation reaction proceeds under mild conditions in the absence of an additional acid catalyst and has been used in the synthesis of dimethyl sulfomycinamate, the acidic methanolysis degradation product of the sulfomycin family of thiopeptide antibiotics.     

Factors affecting the efficiency and stereoselectivity of α-amino acid synthesis by the Petasis reaction

The use of chiral secondary amines containing only one branched substituent has been shown to give optimal yields and stereoselectivities in the preparation of α-amino acids using the Petasis reaction. While the use of chiral primary amines generally gives products in low to moderate diastereoselectivity, chiral secondary amines generally give products in >95:5 diastereoselectivity. Additionally, the use of amines with two chiral (and by definition, branched) N-alkyl substituents results in significantly reduced yields with respect to to secondary amines with one or no branched N-alkyl substituents.     

Copper-mediated synthesis of N,N''''-diarylhydrazines from boronic acids

N,N0-Diarylhydrazines have been prepared via the reaction of N-Boc-aryl hydrazines with boronic acids mediated by copper acetate. This mild reaction condition tolerates the presence of a variety of functional groups.     

Synthesis, structure and hydrogenation catalytic activity of [Ru3(μ3,η-ampy)(μ,η:η-PhC=CHPh)(CO)6(PPh3) (Hampy = 2-amino-6-methylpyridine)

The compound [RU₃(μ₃,η²- -ampy)(μ₃η¹:η²-PhC=CHPh)(CO)₆(PPh₃)₂] (1) (ampy = 2-amino-6-methylpyridinate) has been prepared by reaction of [RU₃(η-H)(μ₃,η²- ampy) (μ,η¹:η²-PhC=CHPh)(CO)₇(PPh₃)] with triphenylphosphine at room temperature. However, the reaction of [RU₃(μ-H)(μ₃, η² -ampy)(CO)₇(PPh₃)₂] with diphenylacetylene requires a higher temperature (110°C) and does not give complex 1 but the phenyl derivative [RU₃(μ₃,η²-ampy)(μ,η ¹:η² -PhC=CHPh)(μ,-PPh₂)(Ph)(CO)₅(PPh₃)] (2). The thermolysis of complex 1 (110°C) also gives complex 2 quantitatively. Both 1 and 2 have been characterized by0 X-ray diffraction methods. Complex 1 is a catalyst precursor for the homogeneous hydrogenation of diphenylacetylene to a mixture of cis- and trans -stilbene under mild conditions (80°C, 1 atm. of H₂), although progressive deactivation of the catalytic species is observed. The dihydride [RU₃(μ-H)₂(μ ₃,η²-ampy)(μ,η¹:η²- PhC=CHPh)(CO)₅(PPh₃)₂] (3), which has been characterized spectroscopically, is an intermediate in the catalytic hydrogenation reaction.     

Efficient synthesis of halohydroxypyridines by hydroxydeboronation

This paper describes a general method for the synthesis of halohydroxypyridines from novel halopyridinylboronic acids and esters recently described by some of us. Halopyridinylboronic acids and esters have been efficiently hydroxydeboronated under mild conditions by employing hydrogen peroxide or meta-chloroperbenzoic acid. These hydroxylations take place regioselectively without other oxidation (N-oxide formation).     

Rh-catalyzed addition of boronic acids to alkynes for the synthesis of trisubstituted alkenes in a biphasic system - Mechanistic study and recycling of the Rh/m-TPPTC catalyst

The versatile preparation of trisubstituted alkenes via selective Rh-catalyzed arylation of alkynes is described in water and in a water/toluene biphasic system. For hydrophobic alkyl alkynes, the reaction afforded either alkenes or dienes depending on the temperature and the solvent conditions. Aryl, heteroaryl, silylated and alkyl substituted alkynes reacted equally well with various boronic acids, leading regioselectively to functionalized alkenyl derivatives in high yields (65-99%). The mechanism was investigated in toluene/water mixture or water and involves a vinylrhodium complex. The efficient recycling of the Rh/m-TPPTC system is disclosed with excellent yield (92-96%) and purity of the alkene.     

Kinetic equation for reversible heterogeneous catalytic reactions

It is demonstrated that when operating far from equilibrium, despite the non-linearity of a complex reaction system, the overall rate of a heterogeneous catalytic reaction is expressed by a classical equation, where the equilibrium constant is determined by the ratio of constants of the forward and reverse reaction, which do not include the lateral interactions in the adsorbed layer.     

New method for the synthesis of 2-phenylproline and its derivatives

A new method has been developed for the synthesis of 2-phenylproline and its derivatives by intramolecular cyclization of the corresponding derivatives of N-(3-chloro-or 1-oxo-3-chloropropyl)--phenylglycine under phase transfer catalysis conditions.A. L. Mndzhoyan Institute of Fine Organic Chemistry, National Academy of Sciences of the Republic of Armenia, 375014 Yerevan, Armenia; e-mail: rafael@msrc.am. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 488–492, April, 2000.     

A new protocol for synthesis of bifunctional alkynyl[vinyl or (E)-alkenyl]substituted organosilicon compounds

A new efficient route for selective synthesis of various, novel alkynyl(vinyl)substituted silicon (6) and alkynyl[(E)-alkenyl]substituted silicon compounds (9) via silylative coupling of alkynes and their products catalyzed by ruthenium(+2) complexes is described. The tandem procedure facilitates the formation of 9 synthesized in a high yield and stereoselectivity by a sequential silylative coupling of terminal alkynes with divinylsubstituted silicon compounds followed by silylative coupling reaction of 6 with styrenes in the presence of ruthenium hydride complexes ([RuHCl(CO)(PR₃)_3−n]; R = Cy (n = 1), i-Pr (n = 1), Ph (n = 0)).     

Kaiser oxime resin-derived palladacycle: A recoverable polymeric precatalyst in Suzuki-Miyaura reactions in aqueous media

Representative cross-coupling reactions of aryl bromides with different types of aryl-, alkyl, trivinylboroxine-pyridine complex, and alkenylboronic acids are performed using a polymer-bonded palladacycle derived from Kaiser oxime resin as precatalyst and potassium carbonate as base under water reflux. These processes afford biphenyls, alkylbenzenes, styrenes, and stilbenes, respectively. The same boronic acids can be cross-coupled with representative allyl and benzyl chlorides using KOH as base in aqueous acetone at 50 °C providing allylbenzenes, diarylmethanes, and 1,4-pentadienes. The palladated polymer can be recovered by filtration and reused during 3-9 cycles with up to 5% of Pd leaching in each run. Very low Pd leaching levels in the crude product can be determined by ICP-OES analyses. The reaction does not work when Hg(0) is added. TEM analyses from the solution indicate the formation of Pd nanoparticles.     

Palladium-catalyzed direct coupling reaction of propargylic alcohols with arylboronic acids

The direct coupling of propargylic alcohols with arylboronic acids has been achieved using palladium catalyst. Various propargylic alcohols and arylboronic acids can be coupled to afford the corresponding allenic and propargylic arenes, which are selectively produced depending on the substituent on the propargylic alcohol, respectively.     

Cationic ruthenium complex of the formula [RuCl(2,6-diacetylpyridine)(PPh3)2]BArF and its catalytic activity in the formation of enol esters

A new ruthenium 2,6-diacetylpyridine complex was synthesized and applied in the atom-economic synthesis of enol esters through Markovnikov-directed addition of carboxylic acids to terminal alkynes. The ruthenium complex [RuCl(dap)(PPh₃)₂]⁺BArF^? was synthesized from [RuCl₂(PPh₃)₂] and the corresponding ligand 2,6-diacetylpyridine (dap). The complex was characterized structurally. The new ruthenium complex was utilized under ambient conditions as a catalyst in the Markovnikov addition of carboxylic acids to terminal alkynes to afford the corresponding enol esters in 93% to 52% isolated yields (85?°C, 16?h reaction time, 1?mol% catalyst loading).     

Nickel(II)-catalyzed addition reaction of arylboronic acids to isatins

A Ni-catalyzed addition of arylboronic acids to isatins was first developed. The reaction, driven by Ni(acac)₂ and dppp as the phosphine ligand, gave 3-aryl-3-hydroxy-2-oxindoles in up to 97% yield. Scopes of benzyl-protected isatins and arylboronic acids were examined. Substituted phenylboronic acids along with fused-ring and heterocyclic boronic acids reacted with isatins smoothly. Preliminary asymmetric catalysis was investigated as well, showing moderate enantioselectivity. The mechanism was also described.