Synthesis of functionalized CF3-containing heterocycles via [2,3]-sigmatropic rearrangement and sequential catalytic carbocyclization

A new efficient access to functionalized CF₃-substituted and nitrogen or sulfur-containing heterocycles has been developed directly from diazocompounds CF₃C(N₂)Z (Z=CO₂Me, P(O)(OEt)₂). The method is based on the direct selective synthesis of doubly unsaturated substrates followed by metal-mediated carbocylization. The first step has been performed by Cu(II)-catalyzed [2,3]-sigmatropic rearrangement of propargyl- or/and allyl-containing sulfur and nitrogen ylides leading to fluorinated enynes, diolefins, and especially allenynes derivatives. The second step involves their carbocyclization via ring closing metathesis and Pauson-Khand reaction.     

Synthesis of six-membered cyclic siloxanes via enyne metathesis with a ruthenium catalyst generated in situ

The catalytic system in situ generated by combination of [RuCl₂(p-cymene)]₂ as a ruthenium source, 1,3-bis(mesityl)imidazolinium chloride (MesH₂ImCl) as a bulky electron-releasing carbene precursor and cesium carbonate as a base, is shown to be an efficient catalyst for the metathesis reaction of propargylic allylsilyl ethers R¹---CCCR₂---O---SiMe₂---CH₂CH=CH₂. The metathesis products, the cyclic siloxanes, were obtained after complete conversion of the enynes in 67–87% isolated yields. These six-membered ring compounds contain the 1,3-diene unit that is used in Diels–Alder reaction and give access to heterobicyclic derivatives. The resulting cyclic siloxanes are selectively opened under oxidative conditions with H₂O₂ to afford allylic diols, with fluoride to form conjugated triene and under hydrogenation conditions with Pd/C catalyst to give a tetrasubstituted alkene.     

One pot Pd(OAc)2-catalysed 2,5-diarylation of imidazoles derivatives

The regioselective 2- or 5-arylation of imidazole derivatives with aryl halides using palladium catalysts has been described in recent years; whereas the arylation at both C2 and C5 carbons of imidazoles in high yields has not been performed. We found conditions allowing the access to these 2,5-diarylimidazoles via a one pot reaction. The choice of the base was found to be crucial to obtain these products in high yields. Using CsOAc as the base, DMA as the solvent and only 2 mol % of the phosphine-free Pd(OAc)₂ the catalyst, the target 2,5-diarylated imidazoles were obtained in moderate to good yields with a wide variety of aryl bromides. Substituents such as fluoro, trifluoromethyl, formyl, acetyl, propionyl, ester, nitro or nitrile on the aryl bromide were tolerated. Sterically congested aryl bromides or heteroaryl bromides can also be employed. Surprisingly the nature of the substituent at position 1 on the imidazole derivative exhibits a huge influence on the reaction.     

Ruthenium‐Catalyzed Synthesis of Functionalized Dienes from Propargylic Esters: Formal Cross‐Coupling of Two Carbenes

Cross‐coupling carbenes : The coupling of a propargylic ester with a diazoalkane in the presence of [RuCl(cod)Cp*] catalyst leads to the formation of functionalized conjugated dienes with high stereoselectivity. The reaction involves the cross‐coupling of a vinylcarbene fragment, arising from a ruthenium‐catalyzed propargylic ester rearrangement, with a diazoalkane carbene.

     

Tandem isomerization/Claisen transformation of allyl homoallyl and diallyl ethers into gamma,delta-unsaturated aldehydes with a new three component catalyst Ru3(CO)12/imidazolinium salt/Cs2CO3

The three component catalyst Ru3(CO)12/1,3-bis(2,6-diisopropylphenyl)imidazolinium chloride/Cs2CO3 (molar ratio 1:3:6) successively promotes both allyl to vinyl isomerization and Claisen rearrangement from allyl homoallyl and diallyl ethers to selectively afford gamma,delta-unsaturated aldehydes.     

Nouveaux composes heterotrinucleaires fer—ruthenium a ponts hydroxo et hydruro

Two new types of heteropolymetallic complexes FeRu₂(μ-OH)₂(CO)₈(PR₃)₂ and FeRu₂(μ-H)(μ-OH)(CO)₈(PR₃)₂ have been obtained in acetone and isopropanol, respectively, from the reaction of FeRu₂(μ-Cl)₂ complexes with bases. They contained a Ru---Fe---Ru bent-chain with the bridging groups holding the ruthenium atoms.     

Discovery of new fluorescent materials from fast synthesis and screening of conjugated polymers

A combinatorial approach was developed for the synthesis and the screening of a large variety of conjugated polymers. The parallel synthesis of 96 polyaryleneethynylene derivatives was performed on a 12 x 8 format from diethynyl and dibromoaryl building blocks, via a palladium-catalyzed carbon-carbon coupling reaction. The qualitative distinction between fluorescent and nonfluorescent polymers as well as between the different emission colors were obtained from a simple visual test or via a 96-well plate reader spectrofluorimeter. New solid-state blue-emitting polymers were detected.