Overall 46 papers resulted. Aryl iodides and bromides are efficiently reduced with Na-alcoholates by e-catalysis. H-atom transfer from the weak C-H bond in Na-alcoholates results in ketyl radical anions, that act as SET-reductants. The sigma-bond activation in anionic radicals served as basis for development of e-catalyzed alkenyl/alkynyl-migrations and allylations. We used ethereal solvents as radical chain reductants and even less activated aryl chlorides could be reduced via this e-catalyzed process.
We studied the electrochemical approach to initiate e-catalyzed transformations. Further, we investigated thermal homolysis of deprotonated pinacols and used non-thermal plasma for initiation of e-catalyzed reactions. We tackled the SET-reduction of acyl azoliums to give ketyl radicals. Via strategy, a synthesis of β-trifluoromethylated alkyl aryl ketones via cooperative NHC/photoredox catalysis was developed. We published the direct α-acylation of alkenes via NHC, sulfinate, and photoredox cooperative triple catalysis. In addition, the dearomative aroylfluorination of benzofurans and indoles was achieved with aroylfluorides using NHC/photoredox catalysis.
The acidity of radical anions has been in focus using theory. We also investigated heteroarene syntheses applying e-catalysis and hydrazones were found to be valuable radical acceptors. Often perfluoroalkyl iodides, that are SET-reduced by radical anions occurring as intermediates in e-catalyzed transformations, were used as C-radical precursors. We also established electron-catalyzed α-perfluoroalkyl-β-heteroarylation of various alkenes with perfluoroalkyl iodides using quinoxalin-2(1H)-ones as radical acceptors. For less reducing radical anions, I(III)-reagents with higher reduction potential were used as radical precursors. Thus, I(III)-chemistry was applied to the regio- and stereoselective perfluoroalkyltriflation of alkynes using phenyl(perfluoroalkyl)iodonium triflates as C-radical precursors. Moreover, a metal-free direct alkene-C-H cyanation was developed. Alkynyl-I(III)-species were used as C-radical trapping reagents of redox-catalyzed alkene amidoalkynylations. To this end, a novel amidyl radical precursor that allows generating an N-radical via SET-oxidation was developed. This N-radical precursor was used in an alkene amidofluorination and in a carboamination of unactivated alkenes.
We introduced alkenyl boron ate complexes as radical acceptors in electron-catalyzed radical-polar crossover reactions. This approach was extended towards the preparation of α-chiral ketones. Amidyl-radical induced radical polar cross/over in vinyl boronates were established. We used the B-ate chemistry in alkaloid synthesis and developed a protocol for the hydrodeboronation of alkyl B-ate complexes. The hydrodeboronation reaction was applied to a radical alkene hydromethylation. B-ate complexes were used in transition-metal free C-H a-arylation or a-alkylation reactions using a novel coupling strategy. We showed that 1,n-bisborylalkanes can be prepared via boron migration using diboron ate complexes. Along these lines, radical 1,2-boron migration is a key step in the 1,3-difunctionalization of allylboronic esters. In addition, catechol diborane was found to be an efficient alkyl radical borylation reagent. For example, mild electron-catalyzed alkene 1,2-perfluoroalkylborylation was realized. Meanwhile, we also found that alkyl iodides and aryl iodides can be converted to the corresponding boronic esters under very mild and practical conditions. Further, conversion of alcohols to their boronic esters (deoxygenative borylation) was achieved by using the same approach. In the B-ate field, we developed a transition-metal-free oxidative cross-coupling of tetraarylborates to biaryls using organic oxidants.
We introduced radical translocating arylating groups for remote C-H arylation of alcohols at unactivated sites and also applied that strategy to the functionalization of α‐C(sp3)‒H bonds in various amides. We further showed that ketenes react with arylsulfonamides to the corresponding amide enolates that upon SET-oxidation and subsequent radical aryl migration provide a-arylated amides. Finally, we entered the area of Fe-H-induced radical alkene hydration and found that nitroarenes can be used in place of dioxygen as radical oxygenation reagents.
