Allylgallium

Ga. Gallium was used to mediate the allylation of carbonyl compounds in water.170 The reaction can also be carried out by using preformed allylgallium reagents.171 The corresponding homoallyl alcohols were obtained in high yields without the assistance of either acidic media or sonication (Eq. 8.72). 

In the presence of GaCl3, allylsilanes add to simple terminal alkynes and silylated alkynes to give m-allylation products.213 A stepwise mechanism including formation and ar-addition of an allylgallium species is plausible for this allylation. 

Allylgallium and propargylgallium compounds can be prepared by the direct reaction of the corresponding bromides or iodides with gallium metal.402,403Gallium enolates are also prepared from a-halo carbonyl compounds with gallium.404... 

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). ... 

Triorganogallium and -indium reagents react with a,/3-unsaturated nitrile, ketone, and ester to give 1,4-addition products regioselectively (Table 31). In contrast, the reaction of allylgallium and allylindium sesquihalides with a,/3-unsaturated carbonyl compounds proceed in a 1,2-addition mode, whereas 1,4-addition takes place with a,/3-unsaturated nitriles.294... 

Homoallylic hydroxylamines and homoallylic hydrazines are synthesized in excellent yields from aldonitrones and hydrazones in aqueous media with allylgallium reagent in the presence of O.lequiv. of NH4G1 or Bu4NBr. The reaction rate can be increased dramatically under microwave activation (Scheme 129).416... 

Later the same group reported that a-bromo carbonyl compounds could be added to terminal alkenes [108] or coupled with allylgallium [109] through intermolec-ular radical reactions still initiated with triethylborane. Another remarkable example was reported by Miyabe et al. They described the indium [110] or triethylborane [111]-mediated radical addition of alkyl iodide to electron deficient C=N bond and C=C bond in water (Eq. 10). 

Organogallium(III) compounds have the ability to undergo radical reactions via homolytic C-Ga bond cleavage as examined by Oshima and Yorimitsu. Allylgallium... 

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