Nickel-Catalyzed Asymmetric Hydrovinylation

Under particularly mild conditions, a Ni-catalyst based on (] , Sc, Sc)-26 gave quantitative conversion of 11 with 84.9% selectivity for the desired product 23 and an excellent enantioselectivity of 94.8% (S) (entry 5). Moreover, the catalyst system proved extremely efficient and remarkably robust for the hydrovinylation of 11. Almost 90% conversion and perfect chemoselectivity were achieved within 4 h at -65 °C even at a substrate/nickel ratio of 4600 1 (entry 6a). Further 

At present, phosphoramidites represent the most promising ligand class for the hydrovinylation reaction, both for the excellent activities and enanioselectivities. The synthetic potential embraces not only styrene and styrene derivatives but also norbornene [54] and 1,3-dienes [55]. 

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The homo- and cross-addition of alkenes catalyzed by a transition-metal provided another economical way of forming C-C bonds.155 These reactions are carried out by using nickel, palladium, or ruthenium phosphine complexes to yield vinylarenes and some can occur in aqueous media. By using carbohydrate-derived ligands, asymmetric hydrovinylations can be carried out in aqueous conditions.156... 

Asymmetric hydrovinylation.1 The reaction of ethylene with 1,3-cyclohex-adiene catalyzed by bis(l,5-cyclooctadiene)nickel, diethylaluminum chloride, and 1 gives ( + )-(S)-3-vinyl-l-cyclohexene (2) in quantitative yield and 93% ee. Related ligands prepared from (S)-proline and D-ephedrine are less effective for asymmetric hydrovinylation. 

Keywords Asymmetric hydrovinylation. Ethylene, Vinylarene, Diene, Norbornene, 2-Arylpro-panoic acid. Nickel, Palladium, tt-Allylnickel bromide, Phospholane, Ligand timing, Hemila-bile hgand. Catalyzed cychzation, 1,6-Diene... 

Continuous, selective hydroformylation in supercritical CO2 using (acac)Rh(CO)2 immobilized on silica as catalyst shows certain advantages. A version of asymmetric hydroformylation in this medium has also been reported,. (Subcritical CO2 gas accelerates solventless synthesis involving solid reactants, including hydrogenation and hydroformylation.) The regioselective and enantioselective nickel-catalyzed hydrovinylation of styrenes in supercritical CO2 make 3-arylpropenes available in an optically active form. " Improvement in the performance of the Pauson-Khand reaction in supercritical media... 

Similarly, asymmetric metal-catalyzed hydrovinylation of various other olefins has been investigated, usually catalyzed by nickel systems prepared from Ni(IJ) salts or / -allylnickel halides, activated by Lewis acids such as ethylaluminum dichloride or diethylaluminum chloride, and modified by chiral phosphanes. Surveys of these results are found in more general reviews11-12 and reviews dealing preferentially with this subject -5-7-13 - A... 

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