Novel Oxidative Ugi Reaction for the Synthesis of Highly Active, Visible‐Light, Imide‐Acridinium Organophotocatalysts

Abstract

A newly designed class of acridinium-based organophotocatalysts bearing an imide group at the C9-position is presented. To achieve these unprecedented structures, a synthetic strategy based on a novel straightforward oxidative Ugi-type reaction at the benzylic position of C9-unsubstituted acridanes was developed. The introduction of the imide-unit affords a notable photocatalytic activity enhancement, allowing efficient transformations in different oxidative and reductive visible-light catalytic reactions.

Mesityl or Imide Acridinium Photocatalysts: Accessible Versus Inaccessible Charge‐Transfer States in Photoredox Catalysis

“…In addition, the reduction potential of the excited state of the new catalysts 2 was estimated by combining cyclicvoltammetry and spectroscopic data. [6] Despite the lower reduction potential of 2 a and 2 b ground states compared to 1 a and 1 b, the two imide-based catalysts showed a comparable excited state reduction potential with 1 a and, to our delight, higher than the 9-mesityl derivative 1 b (see Table 1).…”

“…[1,4,5] Aiming at overcoming some of these restraints, we recently developed a new class of C9-imide acridiniumbased photoredox catalysts 2 (Figure 1, top). [6] In this manner, a vast library of imide-acridinium derivatives with comparable or even improved properties than 1 b was achieved. The N-methyl and N-phenyl cyclohexyl derivatives (2 a and 2 b) showed the highest efficiency as photoredox catalysts in all the reactions we tested, showing in all the cases better results than employing 1 b (Figure 1, bottom).…”

Design and application of aminoacridinium organophotoredox catalysts

“…Furthermore, an elegant strategy consisting of an oxidative Ugi-type reaction for the synthesis of a novel class of imideacridinium salts has been developed by Mancheño and Alemán (Scheme 4). 18 Starting from N-substituted acridanes, a coppercatalysed oxidation takes place at the C9 position to give a cationic intermediate that reacts with the isocyanide. After addition of the in situ formed benzoate, the intermediate is concomitantly rearranged in an Ugi-type fashion to produce the C9-substituted imide-acridanes 10.…”

Emerging Organic Photoredox Catalysts for Organic Transformations

“…Novel imide‐acridinium‐based PCs bearing an imide group as the C9‐substituent were synthesized by Alemán, Mancheño, and co‐workers through oxidative Ugi‐type reaction of C9‐unsubstituted acridanes with isocyanide and benzoyl peroxide, followed by aromatization (Scheme a) . Compared to 98 , the optimized 107 and 108 turned out to be both more powerful oxidant and reductant in their excited state, so outperformed 98 in dehydrogenative lactonization of 2‐phenyl‐benzoic acid and reduction of bromo‐ketone derivatives, respectively.…”