New reductive rearrangement of N-arylindoles triggered by the Grubbs–Stoltz reagent Et₃SiH/KO^tBu

Abstract

N-Arylindoles are transformed into dihydroacridines in a new type of rearrangement, through heating with triethylsilane and potassium tert-butoxide.

Benzylic C−H Functionalisation by [Et3SiH+KOtBu] leads to Radical Rearrangements in o‐tolyl Aryl Ethers, Amines and Sulfides

“…This preference for N‐linked substrates is borne out by very recent reductive rearrangements of N‐aryl indoles in the presence of the same reagents, i. e . Et 3 SiH and KO t Bu …”

“…In 2013, Grubbs et al . reported that heating Et 3 SiH with KO t Bu afforded a novel reagent which has since been shown to carry out a wide range of chemical transformations . (Schemes and ).…”

“…As an indication of the range of mechanisms under consideration, both radical and non‐radical mechanisms have been proposed for the silylation reactions of indoles 1 . Our recent efforts have reported novel reactions that provide new information on the diverse pathways open to this reagent …”

Electron injection for aromatic metamorphosis of indole

“…Performing the reaction at −30°C allowed ( E )‐ 4 to isomerize into ( Z )‐ 4 before work‐up. According to the recent report by Tuttle and Murphy, [ 27 ] the radical anion of 3 can fragment before the second electron injection to afford the corresponding distal radical anion, that is, styryl radical/lithium diarylamide connected species. Although I cannot rule out the possibility of Tuttle/Murphy's process operating, I am inclined to prefer the fragmentation from dianion 6 , on the basis of the facile ring‐opening even at −78°C, the exclusive formation of ( E )‐ 4 as the kinetic product, and the necessity of an excess amount of lithium powder, together with the literature.…”

Et3SiH + KOtBu provide multiple reactive intermediates that compete in the reactions and rearrangements of benzylnitriles and indolenines

“…A novel reducing system, consisting of the reagent-pair, triethylsilane and potassium tert-butoxide was reported by Stoltz, Grubbs et al in 2013. 1 The combination of the two reagents has since been investigated by a number of research groups [2][3][4][5][6][7][8][9][10][11][12][13][14][15] and provides a range of distinctive reaction types, arising through an unprecedented menu of reactive intermediates formed in the reaction, including triethylsilyl radicals 1, silanates 2 as hydrogen atom donors to both closed shell molecules and to radicals, and as potential hydride ion donors, and tert-butoxytriethylsilyl radical anions 3 as a very powerful electron donor. Exposing substrates simultaneously to multiple reactive intermediates is not routinely encountered in organic chemistry, other than in modelling of prebiotic conditions, 16 and so the variety of reactive intermediates produced by this reagent pair provides opportunities to witness unusual outcomes.…”