Allylindium transmetallation

Homoallylic alcohols are provided by Pd-catalyzed reaction of iodobenzene, allene and aldehydes (Scheme 16.15) [19, 20]. A nucleophilic allylindium intermediate is generated through transmetallation of a Jt-allylpalladium species with indium. Such a Jt-allylpalladium complex can alternatively be provided through carbopalladation of ArPdl to a proximate acetylene followed by insertion of allene. 

A three-component reaction based on the umpolung of re-allylpalladium (II) complexes indium metal was reported by Grigg and co-workers (Scheme 8.31) [74]. In this reaction, the electrophilic nature of the n-allyl palladium species generated from aryl halides and allenes is reversed by transmetallation with indium metal. The resultant nucleophilic allylindium reagent subsequently adds to the third component - aldehyde [75] or imine [76] - to give the corresponding homo-allylic alcohol 64 or amine 65 respectively. 

Reactions of Allylindium Prepared by Redox Transmetallation with Pd or Ni 698... 

A new preparative method for allylic indium(m) reagents via a reductive transmetallation of 7r-allylpalladium(n) or 7T-allylnickel(n) complexes with indium(i) salts is reported. This method enables the use of a wide variety of allylic compounds, such as allylic chlorides, acetates, and even allylic alcohols, in combination with Pd or Ni catalysts.43-50 7r-Allylpalladium(ii) resulting from the addition of arylpalladium(n) to allene is also transformed by metallic indium to the corresponding allylindium.51-54 Similarly, propargylindium(m) can be prepared from the corresponding propargyl alcohol derivatives.55-58... 

Allylindium, generated by transmetallation of 5-benzyloxy-4-methyl-2-pentenyl(tributyl)stannane, reacts with benzaldehyde leading to the l,5-< /z//-CE)-stereoisomer with a useful level of 1,5-stereoinduction (Equation (13)).151 2-C-branched sugars and C-disaccharides are prepared diastereoselectively by the indium-mediated reaction of 4-bromo-2-enpyranoside (Equation (14)).152... 

Allylgallium sesquibromides can be prepared from allylic bromides and metallic gallium in the presence of a catalytic amount of indium, where the initially formed allylindium is converted to allylgallium. Fast transmetallation of an allyl group from indium to gallium accelerates the formation of allylgallium sesquibromide (Scheme 122). ... 

In the past decade much effort in organoindium chemistry has been devoted to study of carbonyl allylation and aUylindation of carbon-carbon multiple bonds with allylic indium reagents. Apart from the conventional transmetalation of allyl-lifhium or aUyl Grignard reagents with indium(III) halides, a method widely used for preparation of allyhndium(III) compounds is the oxidative addition of metallic indium or indium(I) iodide to aUyhc substrates [3, 6]. Transmetalation of allylstan-nane with indium(III) chloride also gives allylindium(III) [7]. Allylindium(I) was recently prepared by transmetalation of allylmercury with metallic indium in water this compound is regarded as an intermediate in the allylation of carbonyl compounds in aqueous media [8]. A new method of preparation of allylic in-dium(III) reagents - reductive transmetalation of a 7r-allylpalladium(ll) complex with indium(I) salts has been reported this enables the use of a wide variety of allylic compounds and solvents [9]. 

Stannanes and silanes may act as carbanion derivatives that can be activated with suitable Lewis adds. Thus, as shown by Cossy et al. [440], allylstannanes may be transmetalated with InCU to generate allylindium derivatives in situ. The latter can react with aldehydes to give mixtures of syn and anti adducts (with aromatic aldehydes and 2-buten-l-al). With aliphatic aldehydes, only the anti adducts are observed. The authors concluded that product mixtures were partly caused by the kinetic formation of a mixture of indium (Z)- and ( )-allyl esters prior to the condensation. They then allowed the indium species to equilibrate prior to the aldehyde addition and obtained mainly anti adducts (627, 628) (Scheme 130). 

Cooper et al. reported that the cascade reaction of the palladium-catalyzed cyclization and the Barbier-type allylation of the 1,3-diene-aryl iodide 514, the aldehydes 515, and indium gave the heterocycles 516 in good yields (Scheme 154).220b The reaction proceeds through oxidative addition of a C—I bond of 514 to Pd(0) and subsequent insertion of a double bond of 517 to give the jr-allylpalladium intermediate 518. Transmetalation of the jr-allylpalladium 518 with indium leads to the allylindium complex 519, and the following reaction with the aldehydes 515 gives 516. 

The jt-allyl ligand bonded to Pd(II) usually acts as an electrophile and does not react with aldehyde directly. The transmetalation of the allyl ligand from Pd to In produces an allylindium intermediate that is responsible for the C-C bond forming reaction. 

Allylindium(III) and -bismuth(III) dihalides, generated by transmetallation of 5-benzyloxy-4-methylpent-2-enyl(tributyl)stannane, react with aldehydes with useful levels of 1,5-stereocontrol, a 93 7 ratio of 1,5-epimers in favor of the l,5-anti-(E)-stereoisomers typically being obtained using bismuth(III) iodide. These bismuth(III) and indium(III) halide-promoted reactions are of interest since they... 

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