λ³‐ and λ⁵‐Iodanes: Substituent Effects and Pseudorotation/Hypervalent Twisting

Abstract

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.

Oxidation of Thiols with IBX or DMP: One-Pot Access to Thiosulfonates or 2-Iodobenzoates and Applications in Functional Group Transformations

“…We are actively developing oxidation protocols employing IBX, , modified IBXs, , and Oxone. , In 2016, we demonstrated a facile protocol to access sulfonic acids from thiols using Oxone/NaHCO 3 or KBrO 3 . During the study, oxidation of thiols with hypervalent iodanes , like phenyliodine bis (trifluoroacetate) (PIFA, λ 3 -iodane), IBX (λ 5 -iodane), and NaIO 4 (λ 7 -iodane), afforded the disulfide in 84–93% yields at rt within 2–4 h. If a higher equivalent of the oxidant is employed, then the in situ generated disulfides should further oxidize to thiosulfonates in one-pot was surmised. Therefore, organo-λ 5 -iodanes, namely, IBX and DMP, for this tandem transformation were employed.…”

“…It can be assumed that the acetate ligands in DMP can facilitate the ligand exchange process, which can offer thiol addition to the electrophilic hypervalent iodine center of DMP to produce TAP DMP , Scheme and SI, Scheme S7 . The formation of the purported periodinane adduct TAP DMP can also be possible through a SET process .…”

“…We are actively developing oxidation protocols employing IBX, 8,9 modified IBXs, 10,11 and Oxone. 12,13a In 2016, we demonstrated a facile protocol to access sulfonic acids from thiols using Oxone/NaHCO 3 or KBrO 3 .…”

“…It can be assumed that the acetate ligands in DMP can facilitate the ligand exchange process, which can offer thiol addition to the electrophilic hypervalent iodine center of DMP to produce TAP DMP , Scheme 4 and SI, Scheme S7. 10 The formation of the purported periodinane adduct TAP DMP can also be possible through a SET process. 13 We proposed that TAP DMP undergoes a cascade of intramolecular [1,2]-OAc shifts 29 (i.e., through sulfanes 9a and 9b) to produce sulfoxide species 9c.…”