Visible-light-driven spirocyclization of epoxides via dual titanocene and photoredox catalysis

Abstract

We describe the synergistic utilization of titanocene/photoredox dual catalysis driven by visible light for radical opening/spirocyclization of easily accessible epoxyalkynes.

Shining Light on TiIV Complexes: Exceptional Tools for Metallaphotoredox Catalysis

“…In an analogous example, [ 69 ] Shi and co‐workers expanded the use of the photoredox‐active species to the organic chromophore 4CzIPN ( E 00,S ≈ 2.67 eV; E * ox,S ≈ ‐1.18 V vs. SCE in CH 3 CN [ 70 ] ). Its relatively and inexpensive easy preparation represent desirable requisites for its employment as photocatalysts.…”

Radical‐Mediated Non‐Dearomative Strategies in Construction of Spiro Compounds

“…Like many photoredox reactions, it begins with visible light excitation of Ir(dMeppy) 3 Interesting example of dual catalytic system composed of titanocene and 2,4,5,6-tetra(9H-carbazol-9-yl) isophthalonitrile (4CzIPN) as the photosensitizer for the construction of hydroxy-spiro derivatives 149/151 has been recently published by the Shi group. [61] Described protocol rely on the radical opening/ spirocyclization of easily accessible epoxyalkynes 148/ 150 through the synergistic cooperation of catalysts. It is worth to mention that reaction additionally needs Hantzsch ester (HE) as an electron donor to facilitate reaction.…”

“…Interesting example of dual catalytic system composed of titanocene and 2,4,5,6‐tetra(9 H ‐carbazol‐9‐yl)isophthalonitrile (4CzIPN) as the photosensitizer for the construction of hydroxy‐spiro derivatives 149 / 151 has been recently published by the Shi group [61] . Described protocol rely on the radical opening/spirocyclization of easily accessible epoxyalkynes 148 / 150 through the synergistic cooperation of catalysts.…”

Cp2TiIIICl Catalysis in a New Light

“…[24] Recently, a novel photogeneration of Cp 2 Ti III Cl with the aid of a photocatalyst was reported by the Gansäuer group and Shi group (Scheme 1, b). [25,26] This approach is highly attractive because such an environmentally benign process uses organic electron donors instead of super-stoichiometric metallic reductants. However, it can be surprising at first glance because Cp 2 TiCl 2 is well-known for its intrinsic instability under visible light and decomposes with losing a cyclopentadienyl ligand.…”