Search

International audience; The intramolecular [4+2] cycloadditions of dienynes was investigated using cobalt-based catalysts. Substrates without substitution on alkyne moiety were found to react under thermal activation. The use of a cobalt salt as catalyst made reactions cleaner by limiting the formation of byproducts. Cycloadditions with dienynes possessing a substituent on the alkyne pattern occurred only in presence of a cobalt catalyst which displayed a moderate to good activity depending on the substrate patterns.

Palladium(II) acetate in association with secondary phosphine oxides provides an efficient catalytic system for [2+1] cycloadditions starting from oxanorbornene derivatives and tertiary propargyl esters giving rise to vinylidenecyclopropanes. This reaction is specific to bidentate phosphinito-phosphinous acid ligands generated from secondary phosphine oxides. The [2+1] cycloaddition was found broad in scope with a high tolerance to various functional groups. Moreover, vinylidenecyclopropanes were straightforwardly converted into oxabicyclo[3.2.1]oct-2-ene derivatives through a palladium-catalyzed ring-expansion. Finally, the oxa bridge cleavage of oxatricyclic compounds allows the obtention of functionalized 7-membered carbocycles.

We disclosed therein a new reaction of reductive isomerization of methylenecyclopropanes (MCPs) to vinylcyclopropanes (VCPs). On treatment with sodium metal in liquid ammonia, MCPs bearing a C–O bond at allylic position undergo both a reductive cleavage of the C–O bond and an isomerization of the C–C double bond giving rise to VCPs. The scope of the reductive isomerization was investigated and showed a broad applicability since various functional groups are tolerated. MCP substrates were straightforwardly prepared by a palladium-promoted [2 + 1] cycloaddition between norbornene derivatives with alkynes.

International audience; Palladium(II) acetate in association with secondary phosphine oxides provides an efficient catalytic system for [2+1] cycloadditions starting from oxanorbornene derivatives and tertiary propargyl esters giving rise to vinylidenecyclopropanes. This reaction is specific to bidentate phosphinito-phosphinous acid ligands generated from secondary phosphine oxides. The [2+1] cycloaddition was found broad in scope with a high tolerance to various functional groups. Moreover, vinylidenecyclopropanes were straightforwardly converted into oxabicyclo[3.2.1]oct-2-ene derivatives through a palladium-catalyzed ring-expansion. Finally, the oxa bridge cleavage of oxatricyclic compounds allows the obtention of functionalized 7-membered carbocycles.

The diastereoselectivity of the unprecedented coupling reaction depends on the presence of substituents on the bridgehead positions of the substrates.

Several phosphinous acid-coordinated platinum complexes were prepared and characterized. In the presence of secondary phosphine oxide (2 equiv), PtCl2(cod) was converted to a series of cis/trans platinum complexes PtCl2[R1R2POH]2 featuring phosphinous acids (PAs) as ligands (20−29). A balance between the steric and electronic effects of ligands governs their coordination mode. NMR experiments and density functional theory calculations show that the anti conformer for trans complexes is favored by intramolecular H···Cl bonding. PtCl2[R1R2POH]2 treated with NEt3 (1 equiv) gave bimetallic platinum complexes cis-[Pt2(μ-Cl)2{(R1R2PO)2H}2] characterized by 31P NMR and X-ray diffraction. An unusual monometallic platinum complex, cis-[PtCl2{(i-Bu)2PO}2H]−[HNEt3]+ (30), was isolated and characterized as a possible intermediate in the formation of dinuclear species. Silver acetate and triethylamine both reacted with PtCl2[(t-Bu)2POH]2 to yield new bulky Pt(κ2-acetato){[(t-Bu)2PO]2H} platinum complex 31. The structu...

Electron-rich half-sandwich ruthenium complex CpRuI(PPh3)2, generated in situ, catalyzed the coupling reaction of 7-azabenzonorbornadienes with alkynes to form 3a,9b-dihydrobenzo[g]indoles. This transformation involves the cleavage of one C-N bond of the bicyclic alkene and formation of two (C-C and C-N) bonds at the acetylenic carbons. The scope and limitations of the reaction are addressed according to the substitution patterns of the alkyne and of the substituent at the nitrogen atom of the azabenzonorbornadiene.

2-(Pent-4-ynyl)norbornadienes undergo an intramolecular [2 + 2 + 2] cycloaddition in the presence of (nbd)RuCl2(PPh3)2 as a catalyst affording annelated deltacyclenes in good to excellent yields. The usefulness of the reaction is illustrated by the straighforward conversion of pentacyclene 2a into the angularly fused triquinane 19.

International audience; We disclosed therein a new reaction of reductive isomerization of methylenecyclopropanes (MCPs) to vinylcyclopropanes (VCPs).On treatment with sodium metal in liquid ammonia, MCPs bearing a C−O bond at allylic position undergo both a reductive cleavage of the C−O bondand an isomerization of the C−C double bond giving rise to VCPs. The scope of the reductive isomerization was investigated and showed a broad applicability since various functional groups are tolerated. MCP substrates were straightforwardly prepared by a palladium-promoted [2 + 1] cycloaddition between norbornene derivatives with alkynes.

The homo-Diels–Alder (HDA) reaction of norbornadiene (NBD) and internal functionalized alkynes leading to 8,9-disubstituted deltacyclenes using readily available electron-rich phosphine–ruthenium(II) catalysts is described.

Depending on the variation of the temperature and on the nature of the substituent of alk-1-ynes 2, the enantioselectivity of the deltacyclene formation in the cobalt catalysed [2+2+2] cycloaddition of norbornadiene 1 and acetylenes 2, can be achieved with up to 98%. The best enantioselectivities observed around 14 °C are in agreement with the Isoinversion principle (IIP).

A series of 1,6-dienes is cyclized to cyclopentene derivatives under neutral conditions with palladium chloride in ethanol or with in situ generated LPd2+ in acetonitrile.

The stereoselective formation of 8-substituted deltacyclanes by homo Diels–Alder (HDA) reaction using a phosphine modified nickel catalyst generated by reduction of Ni(acac) 2 with alkylaluminums is discussed. Depending on the nature of the alkene and on the nickel catalytic system, fair to excellent exo selectivity are observed. A switch in selectivity favoring the endo -cycloadduct is observed when the polar methoxycarbonyl group substituted alkene is activated with aluminum species.

The title reaction shows general applicability to various functionalized bicyclo[2.2.1]hept-2-enes, such as (I), (IV), (VII), (IX), and (XI) and ynamides.

Cycles everywhere: The selectivity in the transformations of 1,3-diones to carbo- cycles by palladium-catalyzed bisallylic alkylations is strongly dependent of the phosphine that is employed (see scheme). Moreover, synthesized vinylcy- clopentenes can be easily transformed into cyclohexadiene derivatives through a carbon carbon allylic bond cleavage.

[6 + 2] Cycloadditions between cycloheptatrienes with allenes have been investigated. Cobalt salts were found to promote this transformation efficiently. Moreover, this reaction was found to be highly selective since only one regioisomer was obtained with an excellent E/Z-selectivity.

International audience; [6 + 2] Cycloadditions between cycloheptatrienes with allenes have been investigated. Cobalt salts were found to promote this transformation efficiently. Moreover, this reaction was found to be highly selective since only one regioisomer was obtained with an excellent E/Z-selectivity.

Electron-rich half-sandwich ruthenium complex CpRuI(PPh3)2, generated in situ, catalyzed the coupling reaction of 7-azabenzonorbornadienes with alkynes to form 3a,9b-dihydrobenzo[g]indoles. This transformation involves the cleavage of one C−N bond of the bicyclic alkene and formation of two (C−C and C−N) bonds at the acetylenic carbons. The scope and limitations of the reaction are addressed according to the substitution patterns of the alkyne and of the substituent at the nitrogen atom of the azabenzonorbornadiene.

2-(Pent-4-ynyl)norbornadienes undergo an intramolecular [2 + 2 + 2] cycloaddition in the presence of (nbd)RuCl2(PPh3)2 as a catalyst affording annelated deltacyclenes in good to excellent yields. The usefulness of the reaction is illustrated by the straighforward conversion of pentacyclene 2a into the angularly fused triquinane 19.

The electron-rich cyclopentadienylruthenium complex CpRuCl(PPh3)2 turns out to be an efficient catalyst for the regio- and stereoselective cyclopropanation of bicyclic alkenes with tertiary propargylic carboxylates. The reaction provides 1,2,3-trisubstituted cyclopropanes in high yields as a single stereoisomer instead of the expected cyclobutenes via [2 + 2] cycloaddition. Functional groups such as ethers, esters, alcohols, phenols, ketones, esters, carboxylic anhydrides, nitriles, halides, sulfones, imides, carbamates, and azines are tolerated with the catalyzed reaction. An efficient cyclopropanation of cyclobutenes was also demonstrated, providing the strained bicyclo[2.1.0(1,3)]pentane framework.

Herrmann−Beller (H−B) phosphapalladacycle selectively catalyzed the addition of terminal alkynes across one double bond of norbornadiene to afford exo-5-alkynyl-bicyclo[2.2.1]hept-2-enes. The reaction shows general applicability to various functionalized alkynes and bicyclo[2.2.1]hepta-2,5-dienes. Insights into the mechanism of this reaction are discussed.

The cobalt-catalyzed [6+2] cycloaddition of cyclooctatetraene 1 with alkynes 3 affords monosubstituted bicyclo[4.2.2]deca-2,4,7,9-tetraenes 4 in fair to good yields. Due to the valence tautomerism, 1,3,5-cyclooctatriene 2, in equilibrium with bicyclo[4.2.0]octa-2,4-diene A, and alkynes 3 are converted to 10 and 11 according to [6+2] and [4+2] cycloadditions, respectively.

[reaction: see text] The CoI2(dppe)/Zn/ZnI2 system effectively catalyzes the [6 + 2] cycloaddition of cycloheptatriene with terminal alkynes to afford 7-alkyl-bicyclo[4.2.1]nona-2,4,7-trienes in fair to excellent yields. The catalyst proved to be tolerant toward functional groups such as ketone, sulfone, ester, ketal, ether, alcohol, imide, and nitrile. The enantioselective cycloaddition of CHT and phenylacetylene with BINOL phosphoramidite ligand 4 afforded the cycloadduct 3a (R = Ph) in 91% yield and 74% ee.

CpRu(PPh 3 ) 2 I generated in situ by mixing Cp-Ru(PPh 3 ) 2 Cl and methyl iodide catalyzed the [2+2] cycloaddition ol norbornene (or norbornadiene) and disubtituted alkynes to afford functionalized cyclobutenes.

DIBAL-H reduction of cedren-8 (15)-en-9α-ol 3 in refluxing xylene affords an unusual saturated sesquiterpene skeleton 4 resulting from the ring contraction of the α-methylene cyclohexanol moiety into an ethyl cyclopentane ring.

Oxidation of bridged polycyclic alkanes with in situ generated RuO4 occurs by a concerted mechanism involving interaction of the highly electrophilic oxoruthenium species with tertiary unhindered C–H bonds.

Resume La reaction de cooligomerisation des 1-aza 1,3-dienes avec le butadiene, catalysee par le nickel(0) conduit exclusivement a des amines a motif octatrienyle tandis que la meme reaction avec des aldazines conjuguees conduit a des heterocycles a douze chainons.

Catalytic oxidation (hydroxylation) with RuO 4 generated in situ occurs preferentially in tertiary position with retention of configuration on various bicyclic or tricyclic alcanes.

When copper salts are added to a mixture of 3,5-dimethylpyrazole and ethyl-acrylate, a substitution reaction between dimethylpyrazole and ethylacrylate is observed.

Palladium-catalyzed regioselective 1,4-addition of sodium azide to vinylepoxides afford 4-azido-2-alkenols in good yields.

Ring size control in cyclic ether formation derives from conformationally dictated chemoselectivity in Pd(O) catalyzed cyclization of vicinal diol allyl acetates.

Ruthenium-catalyzed oxidation of variously substituted epoxides featuring the bicyclo [2.2.1] heptane skeleton affords β-diketones in fairly to good yields via a Wagner-Meerwein type rearrangement.