Organoindium reagents

Indium is a group IIIA metal and is a congener of aluminum. Considerable interest has developed recently in the synthetic application of organoindium reagents.145 One of the properties that makes them useful is that the first oxidation potential is less than that of 

The reaction is believed to proceed through a cyclic transition state, and the nucleophile is believed to be an ki(I) species.146 147 

A striking feature of the reactions of indium and allylic halides is that they can be carried out in aqueous solution.148 149 150 The aldehyde traps the organometallic intermediate as it is formed. 

The reaction has been found to be applicable to functionalized allylic halides and aldehydes. 

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Allenic alcohols couple with allyl indium reagents at 140°C to give allylic alcohol products. Similarly, (o-hydroxy lactones couple with organoindium reagents. 

In the presence of TMSC1, the organoindium reagent derived from indium and dimethyl bromomalonate adds to a wide range of conjugated enones under mild conditions in a 1,4-fashion, to yield oxo-1,3-diesters (Scheme 91).332... 

The organoindium reagent, prepared from indium metal and bromoacetonitrile, reacts with carbonyl compounds in the presence of chlorotrimethylsilane to give /3-hydroxy nitriles (Scheme 93),336 337 Similarly, indium-mediated coupling of bromoacetonitrile or 2-bromopropionitrile with a variety of aromatic acyl cyanides affords the corresponding aromatic a-cyanoketones in moderate to good yields under mild and neutral conditions (Equation (86)).338 Carbonyl compounds are efficiently transformed into 2,2-dichloro-3-hydroxynitriles by the action of trichloroaceto-nitrile and indium(i) bromide (Scheme 94).339 Bromocyanomethylation of carbonyl compounds is also achieved by the reaction of dibromoacetonitrile and indium(i) bromide.340... 

A method for iV-alkylation of a-amino esters by RCHO and R l employing In/Ag and InCl3 in aqueous MeOH has been developed. It involves formation of organoindium reagents and imines, and their mutual reaction. 

Cyclization. Organoindium reagents participate in a Pd-catalyzed reaction of an allylic ester that contains a triple bond at some distance by addition, leading to a cyclic compound (with a 5- or 6-membered ring). ... 

The organoindium reagent derived from 5-bromo-l,3-pentadiene reacts at the central carbon atom, whereas 1,4-dibromo-2-butyne behaves as a l,3-butadien-2-ylating agent in the presence of indium in aqueous media. ... 

A key distinction from Grignard reagents is that the organoindium reagents are water-tolerant, to the extent that indium-mediated allylations are often carried out in water. The low toxicity of indium also makes this reaction an excellent example of a green synthetic reaction. 

Organoindium reagents can also be used in the crosscoupling reaction with imines via copper(I) chloride catalysis. Copper-catalyzed direct amination of nitrobenzenes with O-alkylhydroxylamines is known however, more general ami-nation and amidation reactions involve activation of aryl halides with CuCl and l,10-phenanthroline(phen) or other sterically well-defined ligands. ... 

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