Allylation Mediated by Indium

The indium-mediated Barbier reaction has certainly become one of the most popular reactions for creating a carbon-carbon bond under aqueous conditions and has led to spectacular developments in recent years. Compared to other metals, indium is resistant to oxidation, hydrolysis, and has a very low first ionization potential (5.79 eV, in contrast to the second one which is quite normal) which confers on it a remarkable reactivity in Barbier-type reactions. In 1991, Li and co-workers reported the first allylation of aldehydes and ketones mediated by indium in water without any additives or special activation [133]. In particular, the use of indium allowed reactions with acid-sensitive compounds [134] or the preparation of complex carbohydrates such as deaminated 

Zero-valent indium can also be generated in situ by reduction of indium(III) halide with metallic zinc or aluminum [141] or even tin [142]. Thus,)3-trifluoro-methylated homoallylic alcohols have been prepared in high yields and with excellent stereoselectivity using indium powder [143] or a mixture of InClj/Sn [144]. 

The regio- and diastereoselectivity of the reaction using y-substituted allyl bromides with aldehydes was carefully investigated by Chan and Isaac [ 145]. The reaction was as expected y-regioselective except when the y-substituent was too bulky (i.e. ferf-butyl group) but gave only moderate anti diastereoselectivity. 

Several other interesting synthetic procedures have recently been reported. Thus, j9,y-unsaturated ketones were synthesized from aqueous aUylation of acy-loyl pyrazoles, whereas tertiary alcohols were obtained with acyloyl imidazoles [153]. A variety of j9-hydroxy esters were prepared efficiently by indium-mediated aUylation of aldehydes using 3-bromo-2-chloro-l-propene followed by ozo-nolysis [154]. Highly functionalized )8-lactams were prepared by aUylation of 

3- azetinediones [155]. The synthetic potential of this chemistry was also demonstrated with the total synthesis of (-i-)-goniofufurone from D-glucurono- 

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