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

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.

Palladium Catalyzed C3-(sp)-H Alkenylation of Pyrroles via a Benzothiazole Directing Group: A Direct Access to Organic Thermally Activated Delayed Fluorescence Materials.

A Pd (II)-catalyzed direct C3-(sp)-H alkenylation of heteroarenes using benzothiazole as a directing group was successfully achieved. A wide range of 2--alkylpyrroles undergo an oxidative coupling with a variety of acrylates to furnish highly regio- and chemoselective E-alkenylation products at the C3 position. An important intermediate complex has been isolated and characterized so as to have an insight into the mechanism.

The Reactivity of Acceptor-Acceptor Diazo Pyrazolones with Allyl Thioethers under Visible Light: Access to Homoallyl Sulfides, Spiropyrazolones - Pesticide Analogues and Photoflow Synthesis.

The novel reactivity of a less selective and more reactive acceptor-acceptor kind of diazo pyrazolone (DIPOL) has been explored under visible light for the first time. We have successfully demonstrated the reaction of DIPOL and different allyl thioethers under blue light to construct a wide variety of products including a pesticidal analogue exclusively in excellent chemoselectivity in good to excellent yields. Moreover, possible side products emanating from ketene were not observed.

Photosensitizer-Free Photoinduced Ground-State Triplet Carbene-Assisted Persistent Aryloxy Radical Generation via Hydrogen Atom Transfer.

The traditional intermolecular O-H insertion strategy is typically associated with the reactivity exhibited by the singlet spin state, or it can alter the spin state from triplet to singlet by hydrogen bonding. Herein, we report diazoarylidene succinimide that generates a persistent ground-state triplet carbene under visible light (Blue LED, 456 nm) without a photosensitizer. This triplet carbene undergoes an intramolecular O-H insertion via hydrogen atom transfer, forming a persistent aryloxy radical without altering its spin state and leading to biologically relevant 2-chromenes.

Umpolung Reactivity of Diazo Arylidene Succinimides: Distal C-H Functionalization of α-Thiocarbonyls from the Reactive Carbenoid Center.

Herein, for the first time we have explored the umpolung reactivity of the vinylogous carbon center of diazo arylidene succinimide (DAS) through rhodium catalysis to achieve [2,3]-Stevens rearrangement of α-thioether esters. The protocol has successfully demonstrated the distal C-H bond functionalization of the α-thioether esters. Alongside, the carbenoid reactivity of DAS has also been achieved with Doyle-Kirmse reaction of allyl/propargyl phenyl sulfides.