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. 2021 Sep 17;86(18):13025-13040.
doi: 10.1021/acs.joc.1c01764. Epub 2021 Sep 9.

Synthesis of Bench-Stable N- Quaternized Ketene N, O-Acetals and Preliminary Evaluation as Reagents in Organic Synthesis

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Synthesis of Bench-Stable N- Quaternized Ketene N, O-Acetals and Preliminary Evaluation as Reagents in Organic Synthesis

Danielle L McConnell et al. J Org Chem. .

Abstract

N-Quaternized ketene N,O-acetals are typically an unstable, transient class of compounds most commonly observed as reactive intermediates. In this report, we describe a general synthetic approach to a variety of bench-stable N-quaternized ketene N,O-acetals via treatment of pyridine or aniline bases with acetylenic ethers and an appropriate Brønsted or Lewis acid (triflic acid, triflimide, or scandium(III) triflate). The resulting pyridinium and anilinium salts can be used as reagents or synthetic intermediates in multiple reaction types. For example, N-(1-ethoxyvinyl)pyridinium or anilinium salts can thermally release highly reactive O-ethyl ketenium ions for use in acid catalyst-free electrophilic aromatic substitutions. N-(1-Ethoxyvinyl)-2-halopyridinium salts can be employed in peptide couplings as a derivative of Mukaiyama reagents or react with amines in nucleophilic aromatic substitutions under mild conditions. These preliminary reactions illustrate the broad potential of these currently understudied compounds in organic synthesis.

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