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A Phosphine-Mediated Dearomative Skeletal Rearrangement of Dianiline Squaraine Dyes

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journal contribution
posted on 26.03.2021, 14:06 by Emily P. Bacher, Kevin J. Koh, Antonio J. Lepore, Allen G. Oliver, Olaf Wiest, Brandon L. Ashfeld
A phosphorus­(III)-mediated dearomatization of ortho-substituted dianiline squaraine dyes results in an unusual skeletal rearrangement to provide exotic, highly conjugated benzofuranone and oxindole scaffolds bearing a C3 side chain comprised of a linear conflagration of an enol, a phosphorus ylide, and 2,4-disubstituted aniline. Employing experimental and computational analysis, a mechanistic evaluation revealed a striking dependence on the acidity of the aniline ortho substituent. Notably, the rearrangement adducts underwent rapid and complete reversion to the parent squaraine in the presence of a Brønsted acid.