A Phosphine-Mediated Dearomative Skeletal Rearrangement of Dianiline Squaraine Dyes

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 Bronsted acid.

Automated summary

A phosphorus(III)-mediated dearomatization of ortho-substituted dianiline squaraine dyes led to the formation of exotic benzofuranone and oxindole scaffolds with a linear side chain comprised of an enol, a phosphorus ylide, and 2,4-disubstituted aniline. Mechanistic evaluation revealed a significant dependence on the acidity of the aniline ortho substituent, with the rearrangement adducts reverting back to the parent squaraine in the presence of a Bronsted acid.