Isomerisation of allylic alcohols

The isomerisation of aUylic alcohols to saturated ketones usually has a strong thermodynamic driving force. The ruthenium NHC complex 62 has been used to catalyse the isomerisation of allylic alcohol 59 which gives ketone 60 as the principal product along with some of the reduction product 61 [32]. The catalyst was water-soluble and the aqueous phase could be re-used for several runs (Scheme 11.15). NHC analogues of Crabtree s catalyst, [IrlPCyjKpyridineXcod)] PFg, were found to be less efficient for the isomerisation of allylic alcohols than... 

The isomerisation of allyl and propargylic alcohols involves the 1,3-shift of an oxygen atom rather than a hydrogen atom. Isomerisation of allyl alcohols can be catalysed by a variety of metal oxo complexes and in this instance the reaction does not involve metal carbon bonds as we will see. One could imagine that allylic metal species can participate in isomerisation of allylic compounds, but for the alcohols themselves this is not an easy reaction. In chapter 13 reactions of allyl acetates and the like, which are more prone to... 

Isomerisation normally leads to the isomer or mixture of isomers predicted by thermodynamic considerations. For the isomerisation of allyl alcohol to propionaldehyde by HCo(CO)4 the following mechanism has been suggested... 

Alkenes are known to isomerise in presence of transition metal complexes. It has been found that isomerisation of allylic alcohols (or ethers) can be performed in aqueous media in presence of Ru(II)(H20)g(tos)2 (tos = p-toluene sulfonate) (Scheme 136). ... 

The 3-aza Cope rearrangement of N-allyl enamines is mediated by Pd(PPh3),/-CF3C00H, while Pd(0), Pd(II), Rh(I) and Ir(I) complexes effect the closely related conversion of allyl imidates Into allylic amides (eqn.24). The Isomerisation of allylic alcohols under oxidative conditions is catalysed by V(0)(acaC)2 or Mo02(acac)2 and can be temperature dependent (eqn.25). ... 

The result of refluxing [Os3(CO)io( i3-Fc-C = C-C = C-Fc)] with H2O in THF was three new cluster compounds in which the bridging butadiene ligand had been partially hydrogenated. The crystal structures and electrochemistry of these new compounds was presented. A series of compounds of which 172 is representative have been prepared and electrochemical studies showed inter-metal communication. " Compound 173 has been synthesised and fully characterised. Its utility in hydrogenation reactions was also presented. Compound 174 has been shown to deliver ees of up to 86% in enantioselective isomerisation of allyl alcohols.49 ... 

Ahlsten N, Lundberg H, Martin-Matute B (2010) Rhodium-catalyzed isomerisation of allylic alcohols in water at ambient temperature. Green Chem 12 1628—1633... 

Kuntz, E., Amgoune, A., Lucas, C. and Godard, G. (2006) Palladium TPPTS catalyst in water C-allylation of phenol and guaiacol with allyl alcohol and novel isomerisation of allyl ethers of phenol and guaiacol./. Mol. Catal. A Chem., 244,124. Kuntz, E.G. (1987) Homogeneous catalysis. .. in water. Chemtech, 17, 570. Cornils, B. (1999) Bulk and fine chemicals via aqueous biphasic catalysis. /. Mol. Catal. A Chem., 143, 1. 

Kuntz E, Amgoune A, Lucas C, Godard G (2006) Palladium TPPTS catalyst in water C-allylation of phenol and guaiacol with allyl alcohol and novel isomerisation of allyl ethers of phenol and guaiacol. J Mol Catal A Chem 244 124—138... 

The nature of the alkali metal cation of the alcoholate group has a strong influence on the rate of isomerisation of allyl ether to propenyl ether, with reactivity in the following order [78] ... 

Allyl alcohol has a bp of 97 °C, and is thus considerably less volatile than any of the above. In the presence of acid catalyst, allyl alcohol can isomerise to propionaldehyde, even though even this acid-catalysed reaction is much slower than the isomerisation of vinyl alcohol to acetaldehyde. There is thus a distict posibility that allyl alcohol can react with any available acid end group to reform the unsaturated... 

Another promising isomerisation process, the atom-economical conversion of allylic alcohols into aldehydes or ketones, was reported in 2006 by Fekete and Joo. Reactions were carried out in aqueous/organic biphasic systems... 

Another isomerisation process, the atom-economical conversion of allylic alcohols into aldehydes or ketones, was reported in 2006 by Fekete and Jo6. Reactions were carried out in aqueous/organic biphasic systems using a water-soluble NHC-Ru complex 44 [eqn (7.11)]. Because hydrogen was needed to initiate the reaction, formation of saturated alcohols was also observed. This side reaction could be partially repressed by adding sodium chloride to the aqueous solution and by buffering its pH around 7. Altogether, the catalytic system proved moderately efficient, but could be reused up to four times upon recycling of the aqueous phase. 

It can be prepared artificially by the action of allyl iodide on an alcoholic solution of thiocyanate of potassium, the latter body being isomerised to the isothiocyanate under the influence of heat. 

Another interesting example of dehydrative C-C coupling involves the alkylation of benzimidazole 36 with allyl alcohol 37, which is catalysed by complex 39 [15], The reaction is believed to proceed by alkene complex formation with the allyl alcohol 37 with loss of water from the NH proton of the NHC ligand and OH of the allyl alcohol to give an intermediate Ji-allyl complex. The initially formed 2-allylbenzimidazole isomerises to a mixture of the internal alkenes 38 (Scheme 11.9). 

The mechanism for allyl alcohol isomerisation has been studied and the presence of alkoxy and oxo groups in the metal catalyst seems to be essential [5], Not only vanadium, but also rhenium and molybdenum analogues are catalyst for this reaction. The mechanism is depicted in Figure 5.8. The substituents at oxygen can be alkyl groups or silyl groups. 

The retrosynthesis involves the following transformations i) isomerisation of the endocyclic doble bond to the exo position ii) substitution of the terminal methylene group by a more stable carbonyl group (retro-Wittig reaction) iii) nucleophilic retro-Michael addition iv) reductive allylic rearrangement v) dealkylation of tertiary alcohol vi) homolytic cleavage and functionalisation vii) dehydroiodination viii) conversion of ethynyl ketone to carboxylic acid derivative ix) homolytic cleavage and functionalisation x) 3-bromo-debutylation xi) conversion of vinyl trimethylstannane to methyl 2-oxocyclopentanecarboxylate (67). 

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