Dearomative Cycloadditions Utilizing an Organic Photosensitizer: An Alternative to Iridium Catalysis

Abstract

A highly efficient, cheap, and organic alternative to the commonly used iridium photosensitizer (Ir[dF(CF 3)ppy] 2 (dtbpy))PF 6 ([Ir−F]) is presented for visible-light energy transfer catalysis. The organic dye 2CzPN surpasses [Ir−F] in selectivity while at the same time being easily accessible in one step. The catalyst is recyclable and, due to its uncharged nature, soluble in nonpolar solvents such as toluene. Furthermore, the scope of molecular scaffolds that are compatible substrates for visible-light catalyzed dearomative cycloadditions is expanded.

Recent advances in visible light-activated radical coupling reactions triggered by (i) ruthenium, (ii) iridium and (iii) organic photoredox agents

“…78 A key advantage of these cyanobenzene-derived photocatalysts over Ru and Ir photocatalysts is their high solubility in non-polar solvents. 79 For example, the catalyst 2CzIPN (72) has a much greater solubility in non-polar solvents than Ir[dF(CF 3 )ppy 2 ](dtbbpy)PF 6 , 13. This was demonstrated with 72 having a maximum solubility in toluene of 1.3 Â 10 À2 M while 13 had a maximum solubility of 7.0 Â 10 À5 M. It has been recently highlighted that the majority of iridium and ruthenium photocatalysts have low solubility in non-polar organic solvents.…”

“…Dearomative rearrangements of naphthols and indoles were achieved with an organic photocatalyst, 2CzIPN (72) (Scheme 210). 79 Under irradiation with blue light (455 nm), Scheme 206 Formation and reaction of a-aminoalkyl radicals.…”

Photochemical intermolecular dearomative cycloaddition of bicyclic azaarenes with alkenes

“…As such, the reaction has mostly been limited to electron-rich arenes or their prefunctionalized derivatives, and intramolecular variants (Fig. 1D), which require multi-step substrate synthesis and offer limited generality (19)(20)(21)(22)(23)(24)(25)(26)(27). Additionally, inferior selectivity has been observed in both the intra-and intermolecular DAC reactions (Fig.…”

Organic thermally activated delayed fluorescence (TADF) compounds used in photocatalysis

“…180) and indoles, and proceeds via an energy transfer mechanism. 365 TADF compounds 2CzPN, 3DPA2FBN and 3DPADIPN were all considered as PCs in the dearomatisation of an indole substrate, providing a reactant to product ratio of 13 : 1, 1.5 : 1 and 3 : 1, respectively, under the same reaction conditions. Despite producing the worst outcome of these three organic PCs, 2CzPN was chosen as the PC for the remainder of the study.…”