Regioselectivity, in metal-catalysed

Miscellaneous. - Several new optically active tervalent phosphorus acid derivatives have been prepared for use as ligands in asymmetric metal catalysed reactions. These include the cyclic diaminophosphines 57, the cyclic bisamino-phosphine 58, and the compounds 59, 60, 61, and 62 containing a 1,1 -binaphthalene group as the chiral inducer. A new diphosphoramidite (63) has been used for improved regioselectivity of rhodium-catalysed hydroformylations of alkenes. A new sterically hindered chiral phosphite (64) derived from glucose and a Cu(I) complex of 64 have been prepared. ... 

The regioselectivity in the metal-catalysed hydroboration of alkyl-substituted alkenes is the same as that with the non-catalysed system, in which the boron atom becomes attached to the less-hindered carbon atom of the alkene. However,... 

C=C double bond of aP-unsaturated steroidal esters. Several reports of addition reactions catalysed by transition metal compounds have also appeared. Diphenyl-phosphine adds to alkyl vinyl ethers with a high regioselectivity, in the presence of nickel(ii) and palladium(ii) complexes, giving the Markownikolf adducts (99). ... 

In the area of synthesis Garegg has surveyed various regioselective reactions which are applied in oligosaccharide synthesis under the title "Challenges and opportunities for organic synthesis with saccharides of biological importance." More specifically a substantial review has dealt with basic aspects of the major issue of the methods available for the preparation of 1,2-asymmetric centres with defined relative stereochemistry, and 1,3-difunctional compounds in which 1,2-difunctional stereorelationships may also be established. A later publication which builds on this will be of more specific relevance in carbohydrate chemistry. More specific topics to have been surveyed are cycloaddition reactions in carbohydrate chemistry and noble metal-catalysed oxidations of carbohydrates. ... 

The further utility of Grignard reagents can be seen in the metal-catalysed regioselective addition of phenylmagnesium bromide to alkyl compounds (69, X = OH, OR, or Cl). Alkyl derivatives (69a, X = Ph) are formed from (69a,... 

Metal-catalysed biaryl formation continues to be of interest, and there has been a theoretical study of reactivity and regioselectivity in biaryl formation involving the cleavage of carbon-hydrogen bonds by a concerted metalation-deprotonation pathway. Various combinations of metal/ligand/base have been evaluated for the arylation of benzene with aryl bromides at high temperatures and pressures. The combination of cobalt(III) acetylacetonate and lithium bis(trimethylsilyl)amide proved to be effective. ... 

The use of transition metal catalysts to effect alkylations, alkenylations, arylations, and acylations in pyridines has been reviewed, and there has been a computational study of the ortho-alkylation of pyridine by scandium-catalysed reactions with alkenes. DFT calculations indicate that the stability of the developing metal-aryl bonds may be important in determining regioselectivity in palladium-acetate-catalysed carbon-hydrogen substitution in heteroarenes. ... 

In this chapter we will discuss a few topics in the area of alkene polymerisations catalysed by homogeneous complexes of early and late transition metals (ETM, LTM). One of the main research themes for the ETM catalysts has been the polymerisation of propene, while industries have also paid a lot of attention to metallocenes giving LLDPE (linear low-density polyethylene, for thinner plastic bags). In less than a decade a completely new family of catalysts has been developed which enables one to synthesise regioselective and stereoselective polymers of a wide variety of monomers. These new catalysts are starting to find application on industrial scale, but as yet only reports on commercialisation of (branched) polyethylene and polystyrene have appeared. 

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