Isomerisations and Rearrangements

Most alkane isomerisations are carried out in the gas phase but sodium azide supported on NaY has been used successfully to isomerise alkanes in the liquid phase. Unfortunately the catalyst system is very sensitive to 

Various substituted styrene oxides have been rearranged to their corresponding phenylacetaldehydes with good yields and selectivities using titanium zeolites in acetone or methanol at temperatures between 30 and 100°C [90]. 

The pinacolone rearrangement of diols to their corresponding carbonyl compounds (e.g. equation 4.16) is promoted by faujasite and pentasil zeolites [91]. HY zeolite performed best at a temperature of 105°C to give yields of up to 83%. 

A complex hydrolysis-elimination-rearrangement of 2-oxo-azetidin-4-thiones induced by silica (e.g. equation 4.17) is used in the synthesis of thiazolines [92]. 

2-Methylnaphthalene isomerises to 1-methylnaphthalene, with very little dimethylnaphthalene being formed, over various zeolites [93]. Silica gel has been used in the synthesis of hydroazulenes with good yields and selectivity [94]. 

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Stutz, A.E. Giycoscience Evimerisation. Isomerisation and Rearrangement Reactions of Carbohydrates, Springer-Verlag New York, Inc., New York. NY, 2001. 

Since examples related to PET mediated isomerisations and rearrangements of alkenes have been intensively covered previously [5, 10,34] and discussion pertaining to photooxygenation reactions have recently been reviewed [35] in... 

Not much attention has been directed to isomerisation and rearrangement reactions in ionic liquids. Beckmann rearrangements of ketoximes have been performed in neat ionic liquids catalysed by phosphorus(V) chlorides and oxides1 301 and Fries rearrangements of phenylbenzoates have been carried out in chloroaluminate ionic liquids with moderate to good selectivity.1 311... 

Stiitz AE (2001) Glycoscience epimerisation, isomerisation and rearrangement reactions of carbohydrates. Springer, Berlin, Heidelberg, New York... 

Werschkun B, Thiem J (2001) Glycoscience Epimerisation, Isomerisation and Rearrangement Reactions of Carbohydrates. Topics in Current Chemistry Vol 215, Springer-Verlag, Berlin, Heidelberg 215 293... 

Easic Principles Practical Photochemistry General Considerations Carbonyl Compounds a-Cleavage Carbonyl Compounds Hydrogren Abstraction Steroids Carbonyl Compounds Cycloaddition Enone and Dienone Rearrangements Alkenes Isomerisation and Rearrangement Alkenes Cycloaddition Alkenes Photo-Cxidation Terpenoids Aromatic Compounds Isomerisation and Cycloaddition Practical Photochemistry Scale-up Aromatic Compounds Substitution and Cydisation Alkaloids Photoinitiated Free-radical Chain Reactions. 

Brief consideration will be given to NMR investigation of intermediates, products and kinetics of reactions. Alkylation, arylation, metalation, reaction with organometallics, thermolysis and thermal rearrangements, isomerisation and many other reactions such as the Wittig, Michaelis and Arbuzov reactions, which are typical of organophosphorus... 

Trans-cis isomerisation and other transformations caused by light often result in inactive products. Triplet quenchers have a stabilising effect in this respect by inhibiting rearrangements (Bullivant and Pattenden, 1974). Another means of stabilisation is the use of pyrethroids in the form of their 1 2 inclusion compounds formed with /J-cyclodextrin (Yamamoto and Katsuda, 1974). 

In order to learn more about the reaction mechanism and the scope of the aniline rearrangement, additional substrates were tested. Experiments with toluidines (methylpyridines) showed a substantial isomerisation and disproportionation of the substrate (Table 4) due to the methyl-shift reaction on the highly acidic catalyst. Selectivities are low due to disproportionation reaction of the reactants and a large amount of di- and trimethylated reactants and several addition products were formed (which explains the missing 60% in the reaction of o-toluidine). 

There has been no lack of attempts to convert lipids into derivatives which could be chromatographically fractionated and from which the original substances could be subsequently recovered. Acetoxymercuri-methoxy adducts are particularly easily accessible derivatives, being formed by reaction of unsaturated compoimds with a solution of mercuric acetate in methanol containing a little acetic acid. This addition reaction takes place quantitatively at room temperature [68]. ci -Com-pounds react 10—20 times faster than fm i -isomers [68]. The imsaturated compounds can be recovered by treating their adducts with hydrochloric acid, without cis-trans isomerisation or rearrangement of the double bond occurring [68]. 

Selected isomerisation, epimerisation and rearrangement reactions will be presented with a view to preparative applications. 

The aim of this account is to ouUine synthetically interesting rearrangements selected from the literature which have not been covered in previous chapters. The following areas will be discussed Unusual cases of isomerisations and epi-merisations as well as rearrangements involving nucleophiles, radical species and reactions leading to ring-contracted products. 

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