Rhodium-catalysed reactions isomerization

In a related intramolecular rhodium-catalysed Mizoroki-Heck-type reaction of an alkene with an aryl iodide, Wilkinson s catalyst (84) gave significant amounts of side-products due to isomerization of the resulting double bond. In contrast to the corresponding palladium-catalysed transformation, the presence of Et4NCl had no beneficial influence either on the reactivity or on the selectivity [57]. 

The RhI-catalysed rearrangement of A-allylaziridines to (Z)-A-alkenylaziridines has been investigated by computational methods and the reaction occurs via a hydrometalation//3-hydride elimination. Alkylidene cycloheptadienes have been prepared via a rhodium(I)-catalysed tandem isomerization of cyclopropylenynes through a [1,5] carbon-carbon migration via an allene intermediate with high Z E selectivities (Scheme 152). ... 

Complexes of rhodium(i) also catalyse the isomerization of bicyclobutanes and it has been demonstrated that the reactions are affected by the structure of the bicyclobutane, the solvent, and the nature of the ligands of the rhodium(i) (Scheme 72). Gassman and Williams have suggested that the metal catalyst, acting as a Lewis acid, attacks a side bond of the bicyclobutane to give the most stable complex, cyclopropylmethyl cation which is the common intermediate for several product types. There have indeed been two reports of an intermediate complex from (530) and PdCl2(PhCN)2 which was stable at -30°C, and its n.m.r. spectrum was recorded. However, there is some... 

The diester 226 undergoes ring-closure to the methylenecyclopentane derivative 227 in the presence of a catalytic amount of chlorotris(triphenylphosphine)rhodium in boiling chloroform saturated with hydrogen chloride. In contrast, if the reaction is catalysed by palladium(II) acetate, the isomeric cyclopentene 228 is produced (equation 115)118. 

The mechanism of the BINAP rhodium complexes catalysed isomerization of allylamines to enamines has been published280. The reaction course and its intermediates have been probed by ab initio calculations281. 

Several syntheses are available to the 13,14-dihydroprostaglandins, some of which are metabolites of the E and F series. The first of these routes [143, 144] started from the formyl derivative (LVII) of the enol ether of cyclo-pentan-l,3-dione which on reaction with ethyl 6-bromosorbate and tri-phenylphosphine followed by selective catalytic reduction afforded the ester (LVIII). A second formylation followed by elaboration with n-hexanoyl-methylenetriphenylphosphonium chloride 1 to the ketone (LIX) which on reduction of the exocyclic double bond and acid-catalysed solvolysis in benzyl alcohol afforded the benzyl ether (LX) and its isomeric enol ether. Reduction with lithium tri-t-butoxyaluminium hydride to the corresponding 15-hydroxy-compound and palladium-charcoal catalysed hydrogenolysis followed by prolonged catalytic hydrogenation with rhodium-charcoal led to ( )-dihydro-PGEi ethyl ester. 

Addition of dicarboethoxycarbene to cycloocta-1,3-diene yields a mixture of cis-and fran -cyclopropane adducts, probably by addition of the singlet carbene on the partially isomerized diene (due to the irradiation). Diastereoselective cyclopropan-ation of a ,/3-unsaturated acetals has been described using a camphor-derived chiral auxiliary. Intramolecular cyclopropenation of a diazo ester, tethered through a naphthalene, to an alkyne was catalysed by rhodium acetate and reported as a efficient method unfortunately, the use of chiral rhodium catalysts gave a less efficient reaction and did not provide high asymmetric induction. ... 

Reviews.—Recent reviews involving olefin chemistry include olefin reactions catalysed by transition-metal compounds, transition-metal complexes of olefins and acetylenes, transition-metal-catalysed homogeneous olefin disproportionation, rhodium(i)-catalysed isomerization of linear butenes, catalytic olefin disproportionation, the syn and anti steric course in bi-molecular olefin-forming eliminations, isotope-elfect studies of elimination reactions, chloro-olefinannelation, Friedel-Crafts acylation of alkenes, diene synthesis by boronate fragmentation, reaction of electron-rich olefins with proton-active compounds, stereoselectivity of carbene intermediates in cycloaddition to olefins, hydrocarbon separations using silver(i) systems, oxidation of olefins with mercuric salts, olefin oxidation and related reactions with Group VIII noble-metal compounds, epoxidation of olefins... 

The product of thermal or of rhodium(i)-catalysed isomerization of bicyclopentane (22) is cyclopentene (23). The thermal reaction occurs at... 

Within the last few years there has been a growing tendency to draw the analogy between the chemistry of organometallic complexes and that of hydrocarbons adsorbed on metal atoms in surfaces. For example, it is postulated that the isotopic exchan between deuterium and alkanes, catalysed by thin films of nickel, palladium or rhodium, occurs via an equilibrium between a- and 7r-bonded metal-organic species [109, 110, 111, 112]. i-Bonded olefins are postulated in Zie er catalysis, see above, in the catalytic deuteration of aromatic complexes [113], and in a variety of isomerization reactions [112, 114, US]. Other intermediate metal-carbon systems which have been proposed in heterogeneous catalytic systems include carbenes , e.g. M= H2 [109], Ji-enyl systems [114] and of course the metal-carbonyl M—CO and bridging carbonyl M- O—M. 

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