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Keteniminium Salts as Key Intermediates for the Efficient Synthesis of 3-Amino-Indoles and -Benzofurans

2020    Dagoneau, Dylan; Kolleth, Amandine; Quinodoz, Pierre; Tanriver, Gamze; Catak, Saron; Lumbroso, Alexandre; Sulzer-Mosse, Sarah; De Mesmaeker, Alain

Herein, we describe a high yielding approach towards the synthesis of 3-amino-indoles and -benzofurans through 6 pi-electrocyclization. This was made possible by taking advantage of the high reactivity of keteniminium salts, formed in-situ by treating with triflic anhydride and 2-fluoropyridine amides bearing at the alpha-position either an aniline or a phenoxy moiety. These mild conditions, on top of furnishing rapidly the 3-aminobenzoheteroles, allow the tolerance of various functional groups. Control experiments were carried out to highlight that the keteniminium is, indeed, in most cases, the reactive intermediate and conformational preferences of such species were investigated through a DFT study.