Addition of Allylindium Reagents to Aldehydes Substituted at Cα or Cβ with Heteroatomic Functional Groups. Analysis of the Modulation in Diastereoselectivity Attainable in Aqueous, Organic, and Mixed Solvent Systems

The stereochemical course of indium-promoted allylations to α- and β-oxy aldehydes has been investigated in solvents ranging from anhydrous THF to pure H 2 O. The free hydroxyl derivatives react with excellent diastereofacial control to give significantly heightened levels of syn -1,2-diols and anti -1,3-diols. Relative reactivities were determined in the α-series, and the hydroxy aldehyde proved to be the most reactive substrate. This reactivity ordering suggests that the selectivity stems from chelated intermediates. The rate acceleration observed in water can be heightened by initial acidification. Indeed, the indium-promoted allylation reaction mixtures become increasingly acidic on their own. Preliminary attention has been accorded to salt effects, and tetraethylammonium bromide was found to exhibit a positive synergistic effect on product distribution. Finally, mechanistic considerations are presented in order to allow for assessment of the status of these unprecedented developments at this stage of advancement of the field.