Oxidation of N‐Alkyl(iso)quinolinium Salts Over TEMPO@Metal‐Organic Framework Heterogeneous Photocatalyst^†

Abstract

Quinolones and isoquinolones are of particular importance to pharmaceutical industry due to their diverse biological activities. However, their synthetic protocols were limited by high toxicity, high energy consumption, poor functional group tolerance and noble metal catalyst. This study concerns the development of a series of TEMPO@PCN-222 (TEMPO: 2,2,6,6tetramethylpiperidinyl-1-oxy; PCN: porous coordination network) composite photocatalysts by coordinating different amount of 4-carboxy-TEMPO with the secondary building units of PCN-222. Upon visible-light irradiation, photogenerated holes in the highest occupied molecular orbital of PCN-222 can smoothly transfer to TEMPO, which can significantly boost the photosynthesis of bioactive (iso)quinolones from readily available N-alkyl(iso)quinolinium salts. TEMPO@PCN-222 exhibits an outstanding catalytic stability and substrate tolerance with a 1methyl-2-quinolinone yield of 86.7 %, over four times that with . This work provides a new route to construct composite photocatalysts from abundant starting materials for efficient photosynthesis of high value-added chemicals.

TEMPO-immobilized metal–organic frameworks for efficient oxidative coupling of 2-aminophenols and aldehydes to benzoxazoles

“…Consequently, over the past decade, various research groups have explored the immobilization of TEMPO-derived nitroxyl radical species onto MOFs. 32–43 Chemically stable Zr-based MOFs have emerged as notable candidates for TEMPO-decorated scaffolds. 33,35–38,41,42 Chmielewski et al initially investigated the catalytic potential of TEMPO-adducted Zr-based UiO-66 and -67, systematically controlling the incorporated TEMPO through a mixed linker strategy.…”

“…32–43 Chemically stable Zr-based MOFs have emerged as notable candidates for TEMPO-decorated scaffolds. 33,35–38,41,42 Chmielewski et al initially investigated the catalytic potential of TEMPO-adducted Zr-based UiO-66 and -67, systematically controlling the incorporated TEMPO through a mixed linker strategy. 33 However, the bulky catalyst group and narrow pore-sized frameworks led to catalysts containing a significant number of missing cluster defects, complicating the prediction of general structure–activity relationships.…”

“…Subsequent research extended the integration of TEMPO into diverse large pore-sized MOFs, including UiO-68, PCN-222, and PCN-226, for application as catalysts in organic reactions. 35,36,41,42 Notably, the prior work on TEMPO-MOF-catalyzed organic transformations is, to our knowledge, limited to one-component oxidation reactions of single-molecule reactants. Leveraging the advantages of homogeneous TEMPO as an efficient catalyst in multi-step or multicomponent reactions, we anticipated that MOF-TEMPO could facilitate a broader range of reactions.…”