Chiral Hypervalent Organo-Iodine(III) Compounds

Abstract

A series of ortho-substituted chiral hypervalent iodine reagents has been synthesized utilizing a zirconium-mediated iodoacylation reaction, which was followed by a stereoselective reduction, methylation, and an oxidation/ligand-exchange sequence. The evaluation of these new compounds as stereoselective electrophilic reagents towards alkenes and ketones is reported. Enantioselectivities as high as 65% have been achieved in the dioxytosylation of styrene and of up to 40% in the oxytosylation of propiophenone. X-ray structure analysis and ab initio calculations on a hypervalent iodine salt have been used to develop a model for rationalizing the stereoselectivities in these reactions with chiral hypervalent iodine reagents. In this model, high enantiomeric excess in the reaction correlates with the relative population of a conformation in which a methyl group on the asymmetric carbon atom is in the axial position. This work provides new opportunities for the synthesis of new and more efficient chiral hypervalent iodine reagents for stereoselective synthesis.