DOI: 10.1002/ejoc.201700512 Microreview Radical Dioxygenation Recent Advances in Radical Dioxygenation of Olefins Raghunath Bag, [a] Pinaki Bhusan De, [a] Sourav Pradhan, [a] and Tharmalingam Punniyamurthy* [a] Abstract: Dioxygenation of olefins is a valuable synthetic tool for the construction of 1,2-diols and α-oxygenated ketones. The use of radical approaches to achieve this direct 1,2-difunctional- ization has recently made considerable progress. The metal- catalyzed reactions employ molecular oxygen and air as the oxidants, whereas metal-free dioxygenation utilizes oxygen and 1. Introduction The selective difunctionalization of olefins is a critical process in the pharmaceutical, petrochemical, and agrochemical indus- tries. Several methods and reagents have been developed for this purpose. [1–4] Recently, the radical-based 1,2-difunctionaliza- tion [5] of olefins has attracted significant attention as an effec- tive and sustainable strategy for the assembly of oxygenated compounds. Examples include dioxygenation, oxytrifluoro- methylation, [6] oxyamination, [7] oxyhalogenation, [8] oxyphos- phorylation, [9] and oxysulfonylation [10] of olefins (Figure 1). Figure 1. Diverse forms of radical oxygenation of olefins. These oxidation processes share a common reaction path- way: firstly, an active radical species, generated in situ, adds [a] Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati 781039, India E-mail: tpunni@iitg.ernet.in http://www.iitg.ernet.in/scifac/tpunni/public_html/ Supporting information for this article is available on the WWW under https://doi.org/10.1002/ejoc.201700512. Eur. J. Org. Chem. 0000, 0–0 © 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1 peroxides. These oxidations are effective under mild conditions, with activated olefins found to be the most successful sub- strates. This microreview covers the recent developments in the radical dioxygenation of olefins, with respect to substrate scope, mechanism, and the advantages and disadvantages of the methods. to the olefinic double bond, resulting in a C-centered radical, followed by the trapping of another active radical center (Scheme 1). Thus, in an overall pattern, two radicals jointly add across a double bond in a vicinal fashion. Among these proc- esses, the dioxygenation of olefins provides an efficient syn- thetic tool for the preparation of 1,2-diols [11] and α-oxygenated ketones, [12] which are important building blocks in synthetic chemistry (Scheme 2). Scheme 1. General mechanism for the radical difunctionalization of olefins. Scheme 2. Multi-electron olefin dioxygenations. For these dioxygenations of olefins, a class of O-centered radical surrogates [13] such as N-hydroxyphthalimide (NHPI), N- hydroxybenzotriazole (HOBt), N-hydroxysuccinamide (NHSI), and N-hydroxamic acid have been extensively studied for sub- stantial elaboration of the carbogenic backbone (Scheme 3). The radicals generated from these N-hydroxylamines through a one-electron oxidation process are active catalytic species and rapidly came to be employed as stoichiometric reagents in reac- tions with olefins for the synthesis of peroxides and alcohols, which are both important synthons in synthetic organic chemis-