Pericyclic Reactions of Radical Cations

Radical Cation Cycloadditions Using Cleavable Redox Auxiliaries

“…Many features of these reactions are synthetically attractive: they often proceed with very low activation barriers, and their regiochemical outcomes generally complement those involving closed-shell neutral alkenes. 1 In the past several years, there has been a renewed interest in the application of radical ion chemistry to synthesis, due in part to the recognition that photoredox catalysis offers a convenient means to access the distinctive reactivity of these odd-electron intermediates under relatively mild and convenient conditions. 2 Recent reports of synthetic transformations involving photogenerated alkene radical cations have included a variety of cycloaddition reactions 3 and anti-Markovnikov hydrofunctionalization reactions, 4 each of which would be challenging to accomplish using alternate synthetic strategies.…”

Direct Enantio‐ and Diastereoselective Oxidative Homocoupling of Aldehydes

“…Additionally, calculated energy barriers, if located, could provide further evidence for the proposed reaction pathway. It should be noted that potential energy profiles of radical species can be challenging because they often proceed on high‐energy surfaces with shallow minima …”

Selectivity in Radical Cation Cycloadditions

“…Mechanistically, radical cation Diels-Alder reactions are generally considered to be stepwise reactions, [16][17][18] as demonstrated by experimental 19,20 and computational [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] studies. The stepwise mechanism is the result of removing an electron from the HOMO (or, less commonly, the addition of an electron to the antibonding orbital in the case of radical anions), weakening the bond and making the bond easier to break.…”

“…One possible reason is the lack of predictability of selectivity due to various competing mechanisms as well as the generally low familiarity of many organic chemists with the selectivity determining factors. This review complements the previous, mechanistically oriented reviews [9][10][11]17,18,[58][59][60] in addressing some of these questions by providing an overview of patterns governing the selectivity that has been observed in ET catalyzed cycloadditions. Using selected literature examples rather than a comprehensive overview, we will discuss the experimental findings and provide an overview of the factors determining them.…”