Substituted pyrrolidine derivatives are obtained via regio- and chemoselective 5-exo-dig radical cyclization of unactivated 1,6-enynes with chalcogens under metal- and oxidant-free conditions.
A new synthetic protocol has been developed for the synthesis of N‐formamide derivatives using ethers as a C1 synthon under metal‐free reaction conditions. The reaction is proposed to proceed through C−H functionalization, C−O cleavage, and C−N bond formation. This protocol is applicable to a variety of primary amines resulting in N‐formamides in moderate to good yields. 1,4‐dioxane was chosen as best C1 synthon after screening with various ethers. Mechanistic studies disclosed that the reaction proceeds through a radical pathway. While using α‐amino ketones a α‐alkylation product was formed rather than formylation. By replacing dioxane with Tetramethylethylenediamine (TMEDA) under standard conditions also gave the N‐formamide derivatives in moderate yields.magnified image
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.
Oximes have been identified as reusable templates for the synthesis of ureas and carbamates by anin situgeneration of carbamoyl oximes under metal-free conditions.
The FeCl3-promoted ring size-controlled oxidative activation of o-alkynylanilines opens up a complementary appealing protocol for poly-N-heterocycle synthesis.
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