Light-mediated sulfonyl-iodination of ynamides and internal alkynes.

We synthesized tetrasubstituted olefins regioselectively and stereoselectively from ynamides and internal alkynes with sulfonyl iodides under blue LEDs in few minutes. The key features are being metal-free, easy to handle, simple, broad in scope, and environmentally friendly. Furthermore, a gram-scale experiment was conducted, and the synthesized corresponding sulfonyl-iodinated products were smoothly altered into various other products.

Time and Atom Economical Regio- and Chemoselective Radical Cyclization of Unactivated 1,6-Enynes Under Metal- and Oxidant-Free Conditions.

We developed time-atom economic regio- and chemoselective sulfonyl radical triggered 5-exo-dig cyclization of unactivated 1,6-enynes with sulfonyl halides under metal, additive-free reaction conditions to achieve highly substituted five-membered heterocyclic compounds. This transformation creates three new bonds, such as C-SO2 , C-C, and active C-I/Br bonds. Importantly, one-pot protocols produce desired products directly from sodium sulfinates and have an additional advantage such as minimising chemical waste, saving time, and simplifying practical aspects compared to existing protocols.

Photoinduced ynamide structural reshuffling and functionalization.

The radical chemistry of ynamides has recently drawn the attention of synthetic organic chemists to the construction of various N-heterocyclic compounds. Nevertheless, the ynamide-radical chemistry remains a long-standing challenge for chemists due to its high reactivity, undesirable byproducts, severe inherent regio- and chemoselective problems. Importantly, the ynamide C(sp)-N bond fission remains an unsolved challenge. In this paper, we observe Photoinduced radical trigger regio- and chemoselective ynamide bond fission, structural reshuffling and functionalization of 2-alkynyl-ynamides to prepare synthetically inaccessible/challenging chalcogen-substituted indole derivatives with excellent step/atom economy. The key breakthroughs of this work includes, ynamide bond cleavage, divergent radical precursors, broad scope, easy to handle, larger-scale reactions, generation of multiple bonds (N-C(sp2), C(sp2)-C(sp2), C(sp2)-SO2R/C-SR, and C-I/C-Se/C-H) in a few minutes without photocatalysts, metals, oxidants, additives. Control experiments and 13C-labeling experiments supporting the conclusion that sulfone radicals contribute to ynamide structural reshuffling processes via a radical pathway.

Unusual C3-acetylation of quinoxalin-2(1H)-one via oxidative C-C and C-O bond cleavages of PEG-400.

Aerobic oxidative tandem conversion of PEG-400 to acetyl radical via C-C and C-O bond cleavages followed by silver-catalyzed menisci-type addition to the C3 position of quinoxalin-2(1H)-one is described. This reaction involves the in situ formation of the acetyl radical from PEG-400 via a sequence of acetaldehyde, 2-oxopropanal and, 2-oxopropanoic acid formation and successive oxidative cleavage to form the acetyl radical. This protocol uses cheap, readily available and environmentally-friendly PEG-400 as the acetyl source and solvent. The in situ generated acetyl radicals from PEG-400 have been coupled to a broad range of electron-deficient quinoxalin-2(1H)-one compounds in a menisci-type reaction.

Regio- and chemoselective synthesis of nitrogen-containing heterocycles via the oxidative cascade cyclization of unactivated 1,n-enynes.

The development of a method for performing radical initiated intramolecular cascade cyclization of 1,n-enynes provided a competent protocol for producing structurally diverse complex heterocycles. Herein, we demonstrate I2/TBHP promoted, solvent controlled, regio- and chemoselective 5-exo-trig or 6-endo-trig radical cyclization of electronically unbiased 1,n-enynes to synthesize nitrogen-containing heterocycles. These metal-free protocols confer access to synthetically robust piperidine motif-bearing iodinated-homoallylic alcohol and pyrrolidine fused cyclopropane rings. The key factor in these methods is operational simplicity, and the environmentally friendly reaction system works under exceedingly mild conditions. Furthermore, the source of hydroxyl groups in the tertiary alcohols is indirectly confirmed with H218O labeled studies. Based on mechanistic studies, all of these cyclizations were initiated through single electron oxidation. The products with active C-I bonds present opportunities for further transformations.

FeCl3-Promoted ring size-dictating diversity-oriented synthesis (DOS) of N-heterocycles using in situ-generated cyclic imines and enamines.

The FeCl3-promoted ring size-controlled oxidative activation of o-alkynylanilines opens up a complementary appealing protocol for poly-N-heterocycle synthesis. When electron-poor π-alkyne iron species combine with cyclic enamines obtained from cyclohexanone and ß-tetralone, they undergo a regioselective 6-exo-dig cyclization to afford the corresponding dibenzo[b,j][1,10]phenanthrolines and 12-benzoylated dihydrobenzo[a]acridine skeletons. Later, these acridine motifs become completely unsaturated due to dehydrogenative aromatization via the aza-allyl oxidation intermediate. We obtained all quaternary carbon centre pseudoindoxyls through the Mannich-type alkylation of 2,3-dihydro-1H-inden-1-one with cyclic ketimines generated from the in situ intramolecular nucleophilic cyclization of o-alkynylanilines.