λ3 - and λ5 -Iodanes: Substituent Effects and Pseudorotation/Hypervalent Twisting.

Hypervalent iodine (III and V) compounds exhibit positional isomerization through pseudorotation or twisting; the latter have been invoked for the stability as well as the reactivity of λ3 - and λ5 -iodanes. By judicious exploitation of sterics, the twisting process in iodanes can be facilitated to promote reactivity. For example, ortho-substitution in λ3 - and λ5 -iodanes accelerates α-tosyloxylation of ketones and oxidation of alcohols. The enhancement of reactivity arises from sterically-induced non-planarity and the resultant weakening of the 3c-4e bonds involving the hypervalent iodine atom. The ortho-substitution constitutes an important strategy to maneuver reactivity, control selectivity, and develop new catalysts, including chiral, for diverse reactions. This review entails coverage of the literature developments in regard to the effect of substituents and twisting/pseudorotation on the stability as well as the reactivity of hypervalent λ3 - and λ5 -iodanes, and the application of the latter for synthetic transformations.