Rh(III)-catalyzed annulated coupling of sulfoxonium ylides and iodonium ylides: a rapid access to isocoumarins

Direct synthesis of isocoumarin skeletons has been realized through Rh(III)-Catalyzed [3 + 3] annulation of sulfoxonium ylides and iodonium carbenes. The synthetic protocol constructed efficiently with the broad functional group...

Rhodium(III)-Catalyzed Cascade C−H Functionalization/Annulation of Sulfoximines with Iodonium Ylides for the Synthesis of Cyclohexanone-1,2-benzothiazines

A highly efficient Rh(III)-catalyzed cascade C−H activation/annulation of sulfoximines with iodonium ylides under metal-oxidant-free conditions has been reported. The fused cyclohexanone-1,2-benzothiazine scaffold is readily achieved with a one-pot process in...

Synthesis and Properties of ortho-t-BuSO2C6H4-Substituted Iodonium Ylides

Iodonium ylides have recently attracted much attention on account of their synthetic applications. However, only a limited number of reports concerning the properties and reactivity of iodonium ylides exist, which is partly due to their instability. In this study, we synthesized several iodonium ylides that bear both an electron-withdrawing group and an aromatic ring with an ortho-t-BuSO2 group. Based on the crystal structures of the synthesized iodonium ylides in combination with natural-bond-orbital (NBO) calculations, we estimated the strength of the intra- and intermolecular halogen-bonding interactions. In addition, we investigated the reactivity of the iodonium ylides under photoirradiation.

[Co(TPP)]–Catalyzed Carbene Transfer from Acceptor–Acceptor Iodonium Ylides via N-enolate Carbene Radicals

Square-planar cobalt(II)-systems have emerged as powerful carbene transfer catalysts for the synthesis of numerous (hetero)cyclic compounds via cobalt(III)-carbene radical intermediates. Spectroscopic detection and characterization of reactive carbene radical intermediates is limited to a few scattered experiments, centering around mono-substituted carbenes. Here, we reveal the unique formation of disubstituted cobalt(III)-carbene radicals derived from a cobalt(II)-porphyrin complex and acceptor–acceptor λ3-iodaneylidenes (iodonium ylides) as carbene precursors and their catalytic application. Particularly noteworthy is the fact that iodonium ylides generate novel bis-carbenoid species via reversible ligand modification of the paramagnetic [Co(TPP)]-catalyst. Two interconnected catalytic cycles are involved in the overall mechanism, with a mono-carbene radical and an unprecedented N-enolate-carbene radical intermediate at the heart of each respective cycle. Notably, N-enolate formation is not a deactivation pathway, and both the N-enolate and carbene radical moieties can be transferred to styrene. The findings are supported by extensive experimental and computational studies.

[Co(TPP)]–Catalyzed Carbene Transfer from Acceptor–Acceptor Iodonium Ylides via N-enolate Carbene Radicals

<b>Abstract: </b>Square-planar cobalt(II)-systems have emerged as powerful carbene transfer catalysts for the synthesis of a variety of (hetero)cyclic compounds via redox non-innocent Co(III)-carbene radical intermediates. Spectroscopic detection and characterization of these reactive carbene radical intermediates has thus far been limited to a few scattered experiments, in part due to the fact that most studies have focused on mono-substituted carbene precursors. In this work, we demonstrate the unique formation of disubstituted cobalt(III)-carbene radicals in reactions between a cobalt(II)-porphyrin com-plex with acceptor-acceptor iodaneylidenes (iodonium ylides) as the carbene precursors. We report detailed spectroscopic characterization of the resulting reactive carbene radical species, and their application in styrene cyclopropanation. In particular, we demonstrate that iodonium ylides generate novel bis-carbenoid species leading to reversible substrate-promoted ligand modification of the commercially available [Co(TPP)]-catalyst. Two interconnected catalytic cycles are involved in the overall catalytic reaction with a mono-terminal carbene radical and an unprecedented N-enolate-carbene radical intermediate as the respective key species for the mono- and bis-carbene cycles. Notably, N-enolate formation is not a catalyst deactivation pathway, and both the N-enolate and the carbene radical moieties can be transferred as carbene units to styrene. The studies provide a detailed picture of the new [Co(TPP)]-catalyzed carbene transfer reactions from iodonium ylides. The findings are supported by detailed and unequivocal characterization of the reactive N-enolate & carbene radical intermediates and their deactivation products (EPR, UV-Vis, HR-MS, NMR, in-situ ATR-FT-IR, SC-XRD), Hammett analysis, mechanistic control experiments, DFT reaction pathway profiling and NEVPT2-CASSCF electronic structure calculations.<br>