Transmetallation in indium compound preparation

The use of InCls for Lewis acid activation of aldehyde substrates leads to rapid transmetalation of the allylic stannane, followed by carbonyl addition reactions of an allyl indium reagent. Premixing of InCb and the allylic stannane in the absence of aldehyde often produces precipitation and poor results. On the other hand, allyl indium reagents have been independently prepared by several procedures, including reductive metalations. Several important reviews describe the methods of preparation and the reactivity of allyl indium compounds. This discussion will be limited to key factors regarding the transmetalation of allylic stannanes in the presence of aldehydes. Stereochemical events leading to the production of anti adducts as major products are illustrated in Scheme 5.2.55. 

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... 

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]. 

Only two methods for the preparation of phenylindium halides have been reported (i) transmetallation of Grignard reagents with indium trihalides [10] and (ii) the reaction of triphenylindium with Br2 or I2 [11]. No work had appeared in the literature concerning the direct preparation of diphenylindium halides from indium metal and aryl halides. The only related work reported was the preparation of pentafluorophenylindium compounds from indium... 

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