One‐electron reduction is commonly used in organic chemistry for the formation of radicals by the stepwise transfer of one or two electrons from a donor to an organic substrate. Besides metallic reagents, single‐electron reducers based on neutral organic molecules have emerged as an attractive novel source of reducing electrons. The past 20 years have seen the blossoming of a particular class of organic reducing agents, the electron‐rich olefins, and their application in organic synthesis. This Review gives an overview of the different types of organic donors and their specific characteristics in organic transformations.

We report the synthesis of acyl azolium salts stemming from thiazolylidenes C_NS, triazolylidenes C_TN, mesoionic carbenes C_MIC and the generation of their corresponding radicals and enolates, covering about 60 Breslow‐type derivatives. This study highlights the role of additives in the redox behavior of these compounds and unveils several critical misconceptions about radical transformations of aldehyde derivatives under N‐heterocyclic carbene catalysis. In particular, the reducing ability of enolates has been dramatically underestimated in the case of biomimetic C_NS. In contrast with previous electrochemical studies, we show that these catalytic intermediates can transfer electrons to iodobenzene within minutes at room temperature. Enols derived from C_MIC are not the previously claimed super electron donors, although enolate derivatives of C_NS and C_MIC are powerful reducing agents.

Polymerization reactions with organic electron donors (OED) as initiators are presented herein. The metal‐free polymerization of various activated alkene and cyclic ester monomers was performed in short reaction times, under mild conditions, with small amounts of organic reducing agents, and without the need for co‐initiators or activation by photochemical, electrochemical, or other methods. Hence, OED initiators enabled the development of an efficient, rapid, room‐temperature process that meets the technical standards expected for industrial processes, such as energy savings, cost‐effectiveness and safety. Mechanistic investigations support an electron‐transfer initiation pathway that leads to the reduction of the monomer.

The first ipso-selenocyanation of arylboronic acids is achieved using selenium dioxide and malononitrile under mild conditions. The reaction is successful even without metal or base in DMSO. The major advantages of this new method are an easy set-up, excellent yields, and the use of odorless and inexpensive selenium reagents. Basic conditions subsequently afford new access to diaryldiselenides in good yields without isolating the organoselenocyanate intermediates.