Oxonium/Sulfonium Ylide Rearrangements to Access Chromenes and Thiochromenes: Concerted or Stepwise Pathway?

Rhodium-catalyzed regio-divergent intramolecular rearrangements of diazo arylidene succinimide (DAS) derivatives have been achieved at room temperature to access bioactive chromene and thiochromene frameworks. Allyloxy and thioallyl-substituted DAS derivatives were strategically designed and synthesized to explore their reactivity for the facile rearrangements. These transformations are proposed to proceed via oxonium as well as sulfonium ylide intermediates and the subsequent homolytic cleavage-radical recombination, followed by [1,2]- and [1,4]-shifts.

Abstract

Dirhodium(II)-catalyzed regio-divergent intramolecular rearrangement of oxonium and sulfonium ylides, generated from diazo arylidene succinimides (DAS), has been achieved at room temperature. Allyloxy-substituted DAS derivatives were strategically designed and synthesized to explore their reactivity under metal catalysis. The transformation is proposed to proceed via oxonium ylide intermediate, followed by [1,2]- and [1,4]-shifts, leading to the chromene framework. This strategy was further extended to _{thioallyl-substituted DASs} to access thiochromenes under mild reaction conditions. For the first time, intramolecular rearrangement has been explored on DAS derivatives to synthesize bioactive chromene and thiochromene scaffolds.

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