Robust Cobalt(II)Porphyrin Catalyzed Stereo-Divergent Coupling of Phosphorous Ylides

Abstract

High catalytic efficiency is a fundamental prerequisite for the industrial adoption of catalytic transformations. However, reactions achieving turnover numbers (TONs) exceeding 10,000 remain rare in photocatalytic areas, which is primarily attributed to insufficient photostability and light-absorption capacity of photocatalysts. Metalloporphyrins, featured by extended π-conjugation systems, exhibit distinct advantages including high molar extinction coefficients, long-lived triplet excited states, and exceptional photostability, alongside distinctive Soret and Q absorption bands. Motivated by these advantageous properties, we herein report a photoinduced cobalt(II) porphyrin-catalyzed aerobic oxidative coupling of phosphorus ylides to synthesize 1,4-enediones. This photocatalytic system is distinguished by an exceptionally low catalyst loading (2.5 × 10^–3 mol%) and achieves a high turnover number (TON) of up to 19,800. Furthermore, capitalizing on the distinct light absorption of cobalt porphyrin across its Soret and Q bands (corresponding to blue and green light regions), a wavelength-regulated stereoselective synthesis of either (Z)- or (E)-1,4-enediones was realized. Besides, benefiting from the strong absorption at the Soret band of cobalt porphyrin, the reaction for (Z)-1,4-enediones proceeds rapidly within 0.5 h under blue LED irradiation, affording a turnover frequency (TOF) of up to 39,600 h^–1. The protocol also demonstrates broad substrate scope, accommodating diverse heterocycles including indoles, thiophenes, and thiazoles. Mechanistic studies implicate the involvement of singlet oxygen (¹O₂) and superoxide anion (O₂•^–), supporting a sequential pathway involving initial oxidation of the phosphorus ylide to a 2-oxo-2-arylacetaldehyde intermediate, followed by a Wittig reaction to yield the (E)-alkene. Subsequent blue LED-induced isomerization then furnishes the (Z)-configured isomers. This study underscores the significant potential of metalloporphyrins as highly robust and efficient photocatalysts for advanced organic synthesis.

Keywords

Cobalt porphyrin / Phosphorous ylide / Wavelength controlled stereoselectivity / 1,4-Enedione / Photocatalysis / Aerobic oxidation / Stereoselective / Singlet oxygen / High TON/TOF value

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2025 SIOC, CAS, Shanghai, & WILEY-VCH GmbH