A. J. Hubert

Ruthenium-catalysed ring-opening metathesis polymerization of cycloolefins initiated by diazoesters

Abstract Addition of catalytic amounts of diazoesters to various ruthenium complexes, including some diruthenium(II,II) tetrakis carboxylates, led to new catalyst systems that promoted the ROMP not only of norbornene (bicyclo[2.2.1]heptene) but also of cyclooctene and cyclopentene. The conversion and the cis content of the polymers varied widely and depended on the nature of the catalyst precursor.

Olefin cyclopropanation reactions catalysed by novel ruthenacarborane clusters

Abstract Novel ruthenacarborane clusters exhibit high activity as cyclopropanation catalysts in reactions between ethyl diazoacetate and alkenes.

Transition-metal-catalyzed reaction of diazocompounds, efficient synthesis of functionalized ethers by carbene insertion into the hydroxylic bond of alcohols

Abstract An Efficient catalytic synthesis of unsaturated ethers by carbene insertion (with diazoesters as carbene precursors) into the OH bond of unsaturated alcohols is reported. The regioselectivity for the OH insertion is high. However, depending on the catalyst counter-ions and the diazoester alkoxy group, addition to the unsaturated centre can be promoted to some extent, yielding then cyclopropyl and cyclopropenyl carbinols. The mechanistic aspects of the reactions are discussed.

Transition metal catalyzed reactions of diazoesters : Cyclopropanation of dienes and trienes

Abstract The regioselectivity of the cyclopropanation of polyenes by cycloaddition of carbenes generated by catalyzed decomposition of diazoesters in the presence of Rh, Pd and Cu catalysts can be controlled to some extent by selecting proper reaction parameters. For a particular diene, the regioselectivity depends both on the catalyst and on the nature of the double-bond (conjugation, substitution). The cyclopropanation of trienes containing both a conjugated diene system and an isolated double bond is reported as an application of these reactions. The practical interest of the present study is further demonstrated by the synthesis of a pyrethroid precursor by the rhodium(II) carboxylates catalyzed-cyclopropanations of 1.1-dichloro-4-methyl-1, 3-pentadiene.

The role of copper(I) complexes in the selective formation of oxazoles from unsaturated nitriles and diazoesters

Abstract The 1,3-dipolar addition of ketocarbenes (generated from diazoesters) to nitriles is promoted at room temperature by palladium acetate and even more efficiently by copper trifluoromethanesulphonate. The reduction of copper(II) to copper(I) is a key step in the catalytic process, as shown by kinetic studies, EPR and polarography.

Rhodium(II) carboxylate-catalysed reactions of diazoesters: evidence for an equilibrium between free carbene and a metal-carbene complex

Abstract A comparative study of alkane functionalisation by ethyl diazoacetate and diethyl diazomalonate, catalysed by various rhodium(II) carboxylates, indicates that different reactive species, presumably a metal-carbene intermediate and the ‘free’ carbene, are involved in the reaction.

Synthesis of iminoaziridines from carbodiimides and diazoesters : A new example of transition metal salt catalysed reactions of carbenes

Abstract Alkyl diazoacetates react with N,N′-diisopropylcarbodiimide in the presence of transition metal salts (e.g. copper triflate or rhodium (II) acetate) to give 1-isopropyl-2-alkoxycarbonyl-3- isopropyliminio-aziridine in good yield. The reaction takes place at room temperature without formation of the formal dimer of the carbene (maleate and fumarate).

Competitive cyclopropanation and cross-metathesis reactions of alkenes catalysed by diruthenium tetrakis carboxylates

Addition of ethyl diazoacetate to a mixture of styrene and norbornene containing a catalytic amount of Ru2(OAc)4 promoted both the cyclopropanation and a selective cross-metathesis of the alkenes.

Effects of secondary interactions on the stereochemical outcome of rhodium (II) carboxylate-catalysed cyclopropanation of olefins

Abstract In cyclopropanation reactions of olefins catalysed by various dirhodium(II) tetracarboxylates, it is shown that besides the well-recognized electronic and steric effets, secondary interactions between the carbenoid complex and the substrate largely determine the stereoselectivity of the cyclopropanes.

Homogeneous catalysis by transition metal complexes. Selective oxidation of cyclohexene by mixed-catalysts containing rhodium(II) complexes

Abstract The oxidation of cyclohexene catalyzed by mixtures of rhodium(II) carboxylates and epoxidation catalysts (V, Mo) has been studies at 55°C under 1 atm of oxygen. The main product of oxidation is 1,2-epoxycyclohexene-3-ol (II), the yield of which depends strongly on the catalytic system used. The best yields (ca 70% at 15% conversion) are attained with mixtures of electron-deficient rhodium carboxylates and a vanadium cocatalyst. The proposed mechanistic scheme involves two distinct steps: initially autooxidation of the olefin occurs to yield cyclohexenly hydroperoxide, which is used to epoxidize preferentially 2-cyclohexen-1-ol.