An important direction in our research are investigations of the mechanisms of reactions involving hypervalent iodine reagents. We study the mechanisms using an array of experimental techniques, such as: kinetics, reactivity studies, isotope labelling, various spectroscopies (NMR, EPR, UV/Vis), and cyclic voltammetry. 1) We have recently demonstrated that the NHC-catalyzed alkynylation of aldehydes with alkynyliodonium salts proceeds via an unusual direct substitution at acetylenic carbon. This is the second reported alkynyl transfer from a hypervalent iodine reagent following such a pathway, instead of the typical β-attack, followed by 1,2-migration. Interestingly, kinetics investigations revealed that the substitution is facile, because the preceding formation of Breslow intermediate from the aldehyde and NHC catalyst was identified as the rate determining step of the reaction. 2) Using a range of experiments, we have investigated the mechanism of the oxidative dearomatizing hydroxylation of phenols. The obtained results provided fresh and significant insights. Namely, the reaction clearly does not follow any of the previously proposed mechanisms that have circulated for last 20 years in the literature. Instead, all the experiments point to a radical-chain mechanism as the true reaction pathway. Such mechanism is, as the only one, able to explain and rationalize all other existing experimental characteristics of the hypervalent iodine(III)-promoted dearomatization of phenols.