Allylindium chiral

Normally, the addition of C-nucleophiles to chiral a-alkoxyaldehydes in organic solvents is opposite to Cram s rule (Scheme 8.15). The anti-Cram selectivity has been rationalized on the basis of chelation control.142 The same anti preference was observed in the reactions of a-alkoxyaldehydes with allyl bromide/indium in water.143 However, for the allylation of a-hydroxyaldehydes with allyl bromide/indium, the syn isomer is the major product. The syn selectivity can be as high as 10 1 syn anti) in the reaction of arabinose. It is argued that in this case, the allylindium intermediate coordinates with both the hydroxy and the carbonyl function leading to the syn adduct. 

Achiral allylic indium reagents and chiral aldehydes. Allylindium reagents generated in water react smoothly with aldehydes and ketones (Scheme 10-99) [196], The reaction of achiral aldehydes and a-oxygenated aldehydes 290 with the allyl indium reagents proceeds smoothly to homoallylic alcohols without the need for external promoters. It is interesting to note that the a-hydroxyl aldehyde was se-leetive for the syn (chelation-eontrolled) product even in water. 

The enantioselective asymmetric allylation of imines has been a synthetic challenge, the initial solutions of which required stoichiometric amounts of chiral allylbor on [87], allylsilane [88], allylzinc [89], or allylindium reagents [90]. Itsuno showed that a chiral B allyloxazaborolidine derived from norephedrine could add to the N trimethylsilyl imine prepared from benzaldehyde in high yield and enantiomeric excess (Scheme 1.22) [91]. Brown later reported that B allyldiisopinocamphenylbor ane is also very effective for the allylation of the same electrophiles, but the addition of a molar amount of water is necessary to obtain high yields [92]. The diastereo and... 

Cook reported that a 3,3 bis(trifluoromethyl) BINOL catalyzed asymmetric addition of allylindium to hydrazones proceeds in modest to good enantioselec tivities (10 92% ee) [90]. The stoichiometric version of this reaction yields much higher enantioselectivities (84 97% ee). Jacobsen later found that a chiral urea catalyst is effective in catalyzing a similar transformation [96]. The bifunctional catalyst 55 bearing a hydrogen bond donor and a Lewis base that are properly... 

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