C–C bond-forming reactions of ground-state aryl halides under reductive activation

Evidence of single electron transfer from the enolate anion of an N,N′-dialkyldiketopiperazine additive in BHAS coupling reactions

“…[17][18][19] One of the most successful additives is the N,N'-dipropyldiketo-piperazine (DKP) additive 7, which was very effective in promoting C-C bond formation both in transition metal-free aryl-aryl couplings and in SRN1 reactions. 18,20,21 It has been proposed that the DKP additive 7, in the presence of KO t Bu, forms an electron-rich enolate anion 8, which donates an electron to the haloarene 1 in the initiation step of the BHAS reaction pathway and, in doing so, forms the captodatively stabilised radical 9 (Scheme 1B). 18 The aim of this project was to look for evidence that the enolate anion of DKP 8 donates an electron to the haloarene, such as 1, to form the captodative radical 9, under the transition metal-free reaction conditions.…”

Room-Temperature and Transition-Metal-Free Intramolecular α-Arylation of Ketones: A Mild Access to Tetracyclic Indoles and 7-Azaindoles

“…The key step in the sequential synthesis of tetracyclic indoles and 7-azaindoles involves an intramolecular α-arylation of indole-derived methyl ketones, 3a – o . The dark reaction of indole 3a (Z = W = CH, R 1 = CF 3 , R 2 = H) with KO t Bu (5 equiv) in DMSO gave the cyclization product 4a in 85% yield (entry 1) . The yield of 4a did not increase in the presence of pinacolone enolate ion or Fe 2+ salts .…”

“…The dark reaction of indole 3a (Z = W = CH, R 1 = CF 3 , R 2 = H) with KO t Bu (5 equiv) in DMSO gave the cyclization product 4a in 85% yield (entry 1). 16 The yield of 4a did not increase in the presence of pinacolone enolate ion or Fe 2+ salts. 17 Lower conversion and reduced yield of cyclized product 4a was found when the reaction was performed over a shorter time or with a lower amount of base (entries 2 and 3).…”

DMSO/t-BuONa/O2-Mediated Aerobic Dehydrogenation of Saturated N-Heterocycles

“…As a consequence, DMSO can be partly deprotonated by sodium tert -butoxide to give dimsyl carbanions . The dimsyl anions have been proposed to serve as electron donors in thermal single electron transfer (SET) reactions with such electron acceptors as iodobenzene (half-wave reduction potential −1.81 V, SCE); therefore, they may be oxidized by the molecular oxygen (half-wave reduction potential −0.75 V, SCE) to give dimsyl radicals. This kind of mechanism was also proposed by Haland and Hawkins with their coauthors.…”