Rhodium catalysts alkoxycarbonylation

Incidentally, cyclopropanation, one of the carbon-carbon bond formation reactions, is a useful reaction by using diazo compounds to give a variety of keto or alkoxycarbonyl cyclopropane derivatives, for example, crythantimates and their analogues as popular insectsides [2]. The cyclopropanation reactions have often been carried out with the use of copper or rhodium catalysts however, this results in stereochemical problems of trans-cis selectivity or asymmetric induction [3]. 

Rhodium(II) acetate was found to be much more superior to copper catalysts in catalyzing reactions between thiophenes and diazoesters or diazoketones 246 K The outcome of the reaction depends on the particular diazo compound 246> With /-butyl diazoacetate, high-yield cydopropanation takes place, yielding 6-eco-substituted thiabicyclohexene 262. Dimethyl or diethyl diazomalonate, upon Rh2(OAc)4-catalysis at room temperature, furnish stable thiophenium bis(alkoxycarbonyl)methanides 263, but exclusively the corresponding carbene dimer upon heating. In contrast, only 2-thienylmalonate (36 %) and carbene dimer were obtained upon heating the reactants for 8 days in the presence of Cul P(OEt)3. The Rh(II)-promoted ylide formation... 

The most frequently used metallic catalysts for acyldiazo- and (alkoxycarbonyl)dia-zomethanes are complexes or salts of rhodium, palladium and copper. Alkenylboronic esters A-silylated allylamines and acetylenes are successfully cyclopropanat-ed with diazocarbonyl compounds under catalysis of one of those metal derivatives. Newly developed metallic catalysts for diazoacetic esters include polymer-bound, quantitatively recoverable Rh(II) carboxylate salts ", Cu(II) supported on NATION ion exchange poly-mer ruthenacarborane clusters, Rh2(NHCOCH3)4 which produces cyclopropanes with substantially enhanced trans (anti) selectivity as shown below and (rj -CsHs)... 

Alkoxycarbonylation of amines. Carbamates can be prepared by reaction of a primary amine with carbon monoxide, oxygen, and an alcohol catalyzed by either 5% rhodium on activated carbon or palladium black and an alkali metal halide, particularly an iodide such as Csl or K1 (equation 1). Essentially no reaction occurs in the absence of the salt. Dialkylureas are intermediates in the reaction, and can be isolated as the major product when less active catalysts such as IrCI, arc used. 

Trost et al. reported the first asymmetric total synthesis of pseudolaric acid B by exploiting a rhodium-catalyzed intramolecular [5-1-2] cycloaddition reaction of a vinylcyclopropane with an alkyne (Scheme 8.2) [4]. The vinylcyclopropane having a tethered alkyne moiety 12 was synthesized from chiral precursors 9 and 11. Treatment of 12 with a cationic rhodium(1) catalyst promoted the [5-1-2] cycloaddition reaction to form a [5.3.0]bicyclic skeleton of 13 in a diastereoselective fashion. A few steps of functional group transformations provided the alkoxycarbonyl... 

Detailed studies were not known until recently although several workers in the field took preventions to make sure that the 1-alkene substrates were not contaminated with enones, dienes, or alkynes. In an m situ IR study combined with high pressure NMR studies, Walczuk has shown how this temporary inhibition takes place and what intermediates are formed. " In situ IR clearly showed the disappearance of rhodium hydride catalyst when these poisons were added the dormant states were slowly depopulated and after all impurities were converted, the hydroformylation of I-octene started, while simultaneously the hydride-resting state of the catalyst was recovered. Enones gave rise to stable alkoxycarbonyl species 18 (Scheme 3) that were slowly converted to ketones after deinsertion of GO. The degree of inhibition depends both on the structure of the inhibitor and on the ligand as yet, the latter has not been fully exploited. 

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