Intramolecular Rhodium Catalyzed Sigmatropic Rearrangement of Diazo-Derived Oxo-nium and Sulfonium Ylides: A Versatile Approach for the Synthesis of Functionalized Chromenes and Thiochromenes

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 and thioallyl-substituted DAS deriva-tives were strategically designed and synthesized to explore their reactivity in these rearrangements. The transformations are proposed to proceed via oxonium or sulfur ylide intermediates, followed by [1,2]- or [1,4]-sigmatropic shifts, leading to chromene and thiochromene frameworks. This strategy employs mild reaction conditions and represents the first applica-tion of sigmatropic rearrangement for the construction of bioactive chromene and thiochromene scaffolds.