Recent advances in acyl radical enabled reactions between aldehydes and alkenes

Abstract

Radical-mediated functionalization of alkenes has been emerging as an elegant and straightforward protocol to increase molecule complexity. Moreover, the abstraction of a hydrogen atom from aldehydes to afford acyl radicals...

Iron-Catalyzed Dearomatization of Biaryl Ynones with Aldehydes via Double C–H Functionalization in Eco-Benign Solvents: Highly Atom-Economical Synthesis of Acylated Spiro[5.5]trienones

“…In the reactions of these aliphatic aldehydes, although replacing the solvent with acetonitrile and raising the reaction temperature to 100 °C improved the yield of the products ( 3as – 3aw ), it was found that it was difficult for the reaction to completely consume 1a even with a prolonged reaction time. Compared with aryl aldehydes, the formation of aliphatic acyl radicals via alkyl aldehyde C­(sp 2 )–H bond cleavage remains relatively rare and challenging . Additionally, the aliphatic acyl radicals generated by the oxidation of aliphatic aldehydes under heated conditions can undergo sequent decarbonylation to form alkyl radicals, a process by which a range of alkylation reactions have been well utilized. , These may be the important reasons for the difficulty and low yields of aliphatic aldehydes in the present dearomatization.…”

“…Compared with aryl aldehydes, the formation of aliphatic acyl radicals via alkyl aldehyde C(sp 2 )−H bond cleavage remains relatively rare and challenging. 18 Additionally, the aliphatic acyl radicals generated by the oxidation of aliphatic aldehydes under heated conditions can undergo sequent decarbonylation to form alkyl radicals, a process by which a range of alkylation reactions have been well utilized. 19,20 These may be the important reasons for the difficulty and low yields of aliphatic aldehydes in the present dearomatization.…”

“…This fact indicates that the oxygen in the newly formed carbonyl group should not come primarily from water. Furthermore, an 18 O-labeling experiment performed by adding 30 equiv of H 2 18O afforded the 18 O-labeled product, which was detected by HRMS with the relative intensity of 82.9% (Scheme 4c; for details, see the Supporting Information). 5e,11b Thus, it can be supposed that the oxygen atom of this carbonyl mainly come from TBHP.…”

“…Initially, a homolytic cleavage of TBHP produced HO• and t-BuO• radicals, which abstracted hydrogen from benzaldehyde (2a) to yield an aldehydic radical and t-BuOH. The benzoyl radical added to the triple bond of 1a to form the vinyl radical A, which underwent 6-exo-trig cyclization to afford the radical intermediate B and was converted to the desired product through one of three possible pathways: (a) combined with BuO 18 O• to form C and afforded 18 O-3aa and t-BuOH, (b) combined with H 18 O• to form D and afforded 18 O-3aa upon oxidation by TBHP, and (c) oxidized to carbocation E, which combined with 18 OH − to form D and afforded 18 O-3aa. It can be seen that while the reaction can proceed without metal salts through pathway b, the Fe ion promoted the formation of t-BuOO•, t-BuO•, and carbocation E and thus catalyzed the reaction via pathways a and b. Additionally, only t-BuOH and H 2 O were byproducts in the whole reaction process.…”

NHC and visible light-mediated photoredox co-catalyzed 1,4-sulfonylacylation of 1,3-enynes for tetrasubstituted allenyl ketones

“…1 b Through radical addition to the unsaturated bond to form a C–C bond, acyl radicals have been utilized in preparing diverse carbonyl compounds. 2 However, radical-coupling reactions between acyl and other carbon-centered radicals are rare. N-Heterocyclic carbene (NHC) catalysis has emerged as an attractive strategy in synthetic chemistry to access value-added organics via the formation of the key Breslow intermediate (BI).…”