Palladium-catalyzed direct arylation of 5-chloropyrazoles: a selective access to 4-aryl pyrazoles

The use of a temporary protection by a chloro group at C5 of pyrazoles allows the synthesis of the 4-arylated pyrazoles, which were previously inaccessible by palladium-catalyzed direct arylation, with complete regioselectivity and in high yields using in most cases as little as 0.5-0.1 mol % Pd(OAc)(2) as the catalyst with electron-deficient aryl bromides. Moreover, from 5-chloro-1,3-dimethylpyrazole, sequential catalytic C4 arylation, dechlorination, catalytic C5 arylation reactions allowed the synthesis of a 4,5-diarylated pyrazole derivative.     

Synthesis of enol esters from terminal alkynes catalyzed by ruthenium complexes

Regioselective enol ester formation results from the addition of saturated and unsaturated carboxylic acids to phenylacetylene in the presence of RuCl₃, RuCl₃/2PR₃ or RuCl₂(PMe₂)(arene) catalysts.     

Erratum

Treatment of complexes of the type Fe(η²-CS₂)(CO)₂L₂ with trifluoroacetic acid provides a convenient route to Fe(η¹-OCOCF₃)₂(CO)₂ L₂ derivatives (L = PPh₃, PMe₂Ph,

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). The latter react with (NO)⁺PF₆^? in acetonitrile to give NO and [Fe(gh¹-OCOCF₃)(NCCH₃)(CO)₂L₂] PF₆ complexes.     

Tandem catalytic carbene addition/bicyclization of enynes. One-step synthesis of fluorinated bicyclic amino esters by ruthenium catalysis

The reaction of diazo compounds with enynes, containing a fluorinated amino acid moiety, in the presence of the precatalyst Cp(Cl)Ru(COD) leads to fluorinated alkenyl bicyclo[3.1.0]hexane and [4.1.0]heptane amino acid derivatives. It is remarkable that the catalyst, in situ generated from ruthenium complex and diazo compound, completely inhibits the ring closing metathesis of enyne to the profit of tandem alkenylation/cyclopropanation with high stereoselectivity. The study shows that the Cp(Cl)Ru moiety in ruthenacyclobutane favors reductive elimination versus expected alkene metathesis. [reaction: see text]     

Synthesis of ruthenium acetylides: new building blocks for molecular electronics

Several ruthenium(II) mono(acetylides) trans-[Cl(dppe)₂Ru---(CC)_n---R] (n=1–4; R=SiMe₃, H) and bis(acetylide) trans-[(dppe)₂Ru(---(CC)₂---R)₂] (R=SiMe₃, H) were selectively obtained and could be used as a new set of building blocks for rigid rod-like structures and further assemblies. Especially, the oxidative coupling of trans-[Cl(dppe)₂Ru---(CC)₃---H] with Cu(OAc)₂ led to the formation of the first Ruthenium(II) binuclear species with 12 carbon atoms between the remote metals. This compound shows two reversible redox processes.     

Organometallic reactions as tools to build new metal-containing conjugated polymers

By using organometallic reactions like Pd-catalyzed C-C coupling, metal-carbon bond formation and silicon-carbon bond cleavage, novel carbon-rich organometallic monomers HC≡C-C₆H₄-C≡C-[M]-C≡C-C₆H₄-C≡CH ( [M] = -Ru(dppe)₂- and (η⁵-C₅H₄)₂Fe) and organic monomers H-(C≡C-C₆H₄)_X-C≡CH (x = 1 to 3) have been obtained. They have been used for the design of novel homo and hetero metal-containing polymers via organometallic polycondensation reactions based on quantitative metal-carbon bond formation.