A cobalt covalent organic framework: a dual-functional atomic-level catalyst for visible-light-driven C–H annulation of amides with alkynes

Abstract

The merger of transition-metal catalysis and photoredox catalysis enables a balance between the elegant chemical transformation and the rational use of light energy. Previously, it was always accomplished with the...

A covalent organic framework-catalyzed visible-light-induced three-component cascade synthesis of trifluoroalkyl and trifluoroalkenyl quinoxalin-2(1H)-one derivatives

“…Then, they were used as heterogeneous photocatalysts in sequence for the visible-light-induced three-component reaction of quinoxalin-2(1 H )-one ( 1a ), phenyl propylene ( 2a ), and CF 3 SO 2 Na under the blue LED irradiation in dioxane at room temperature for 24 h. We observed that most of them were effective for the reaction, delivering the corresponding C3 trifluoroalkyl quinoxalin-2(1 H )-one ( 4aa ) selectively (Table 1, entries 1–5). Possibly due to the competitive BET surface area, 19 2D-COF-5 (constructed using [2,2′-bipyridine]-5,5′-dicarbaldehyde and 4,4′,4′′,4′′′-(1,9-dihydropyrene-1,3,6,8-tetrayl)tetraaniline) substantially enhanced the reaction efficiency. Further screening disclosed that 2D-COF-5 was indispensable for a high substrate conversion (entry 6), and the wavelength of visible light should be 456 nm for the best output of the desired product 4aa (Table S1, see details in the ESI†).…”

“…, oxidation, 13 reduction, 14 cyclization, 15 C–H functionalization, 16 E – Z isomerization, 17 cross-coupling, 18 and cascade C–H bond activation/cyclization. 19 Notably, the diversity of organic building blocks endows 2D-COFs with an unlimited tunability of their photocatalytic performance, providing massive potential to expand their applications to more sophisticated photocatalytic organic processes.…”

“…With the above considerations, and building on our previous studies on photoactive 2D-COF-initiated heterocycle synthesis and modification, 15 b ,16 c ,19 we would like to report a new photocatalytic application of 2D-COFs on the visible-light-induced three-component reactions of quinoxalin-2(1 H )-ones, unsaturated hydrocarbons and CF 3 SO 2 Na (Scheme 1c). With suitable photocatalytic properties and the easy recyclability of an imine-linked covalent organic framework (2D-COF-5), the cascade reaction occurred sustainably and elegantly, delivering a series of C3 trifluoroalkyl and trifluoroalkenyl quinoxalin-2(1 H )-ones efficiently.…”

“…Based on the above results and previous related studies, 7,8 a plausible reaction mechanism for this heterogeneous visiblelight-induced three-component system is outlined in Scheme 4. Firstly, with blue LED irradiation, a powerful oxygen activator reported by us recently, 19 i.e., photo-excited 2D-COF-5*, activates oxygen in the air to 1 O 2 via energy transfer (ET). Then, the singlet oxygen oxidizes CF 3 SO 2 Na to produce the CF 3 radical (I) with the loss of SO 2 .…”

Two-in-one metallaphotoredox cross-couplings enabled by a photoactive ligand

“…transcribed to other synthetically relevant transformations. In certain cases, some ligand-free inorganic metal salts [51][52][53][54][55][56][57][58] and metal-embedded organic frameworks [59][60][61][62][63][64][65][66][67] could achieve cross-couplings in the absence of external PCs, 68 although these systems remain underdeveloped and mostly limited to C-X bond formation.…”