Visible light sensitization of benzoyl azides: cascade cyclization toward oxindoles via a non-nitrene pathway

Abstract

Visible light sensitization of benzoyl azides was examined in reaction with N-phenylmethacrylamides to afford biologically important oxindoles and spirooxindoles via a cascade cyclization under mild reaction conditions. Mechanistic studies suggested a non-nitrene pathway, where triplet benzoyl azides act as the reactive intermediate.

Sulfonylative and Azidosulfonylative Cyclizations by Visible‐Light‐Photosensitization of Sulfonyl Azides in THF

“…Prior reports of photocatalytic reactions of organic azides invoke the formation of reactive intermediates such as nitrogen‐centered radicals,,, azide radicals,,, and nitrenes –,. We therefore hoped that cyclohexa‐2,5‐dienone‐tethered alkyne 1 a , which contains several unsaturated functional groups, would react productively with para ‐toluenesulfonyl azide ( 2 a ) under photocatalytic conditions (Table ).…”

“…The recent, dramatic increase in the use of visible light photocatalysis in synthesis has led to its application in reactions of organic azides, resulting in several interesting new processes . Aryl,–, alkyl, alkenyl, and acyl, azides, as well as azidoformates have been employed in reductions, radical additions to nitriles, nitrene insertions,, rearrangements, aziridinations,, enantioselective enolate aminations, and cascade cyclizations . Azidoiodanes have also been used in radical azidations ,,…”

Visible Light Mediated Synthesis of Oxindoles

“…In this context, in 2017, Chang and co‐workers synthesized 3‐amidooxindoles 6 in moderate to excellent yields by utilizing benzoyl azides 5 as an amine source and N ‐phenylmethacrylamides 2 as a substrate under photocatalytic condition (Scheme 2). [11] The reaction demonstrated ample substrate scope and good functional group tolerance with respect to both benzoyl azides and N ‐phenylmethacrylamides. Besides, the cyclic α , β ‐unsaturated amides 2 were also found compatible under the given reaction conditions, affording the spirooxindoles 7 with single distereomers in moderate to good yields.…”

Photodecomposition of 1H‐Pyrrole Carbonyl Azides: Direct Observation of Singlet 1H‐Pyrrole Carbonyl Nitrenes and Triplet 1H‐3‐Pyrrylnitrene

“…[1] For examples, benzoyl azide PhC(O)N 3 has been broadly used for the synthesis of biologically active hetero-aromatic amides, oxindoles, and spirooxindoles through direct and atom-economic C-H amidation of heteroarenes [2] and cascade cyclization with N-phenylmethacrylamides. [3] Alkoxycarbonyl azides ROC(O)N 3 are useful reagents for the synthesis of reactive aziridines and oxazolidinones through photo-induced spinselective C-H amination [4] and transition-metal catalyzed nitrogen transfer reactions. [5] Similar to other covalent azides such as HN 3 , [6] acyl azides RC(O)N 3 are thermally unstable and may decompose explosively upon either heating or irradiation.…”