Photochemistry is a tremendous research field offering many synthetic possibilities to chemists. Breakthroughs in this area have been notably driven by the implementation of new classes of photocatalysts. Within this context, Bodipy (Boron-dipyrromethene) dyes possess attractive chemical and physical features such as their modularity, strong absorption under visible light irradiation, good thermal and photochemical stabilities, and high fluorescence quantum yields. As such, this class of compounds has found widespread applications in functionalized materials, biology, medicine, or organic chemistry. From an organic-synthetic point of view, excited states of Bodipy dyes have been harnessed in electron and energy transfer reactions. This minireview collates the relevant literature on the applications of these catalysts in synthetic photochemistry and provides some perspectives of this research area.
The combination of oxidative dearomatization and trienamine/enamine activation in a single vessel is described. Under these conditions, a three-bond forming process generates functionalized tricyclic architectures with up to six contiguous stereocenters with excellent stereoselectivities from readily available planar substrates.
An unprecedented organocatalytic asymmetric desymmetrization of para-quinamines leading to functionalized hydroindoles, a common motif in many alkaloids, has been reported. The ability of diarylprolinol silyl ethers to promote iminium and enamine activation of α,β-unsaturated aldehydes in one catalytic cycle is the centerpiece of the strategy involving a challenging aza-Michael/intramolecular cyclization cascade reaction. A range of prochiral para-quinamines and α,β-unsaturated aldehydes were investigated to afford 16 examples of hydroindoles possessing four contiguous stereocenters including one quaternary carbon. The hydroindole structures include multiple orthogonal functionalities, which underwent various transformations.
Game, set, and match: The first regio‐ and enantioselective version of the title reaction is described. The chiral catalyst prepared in situ from CrCl3 and a non‐C2‐symmetric bis(oxazoline) ligand 1 affords the valuable chiral β‐allenols regioselectively in good yields with excellent ee values. R=aryl, alkyl.
We report herein a new catalytic strategy towards asymmetric photooxygenation of β‐dicarbonyl compounds. Our method is based on the synthesis of a bifunctional photosensitizer composed of a quinine organocatalyst grafted to an iodo‐BODIPY framework capable of generating singlet oxygen. The quinine moiety serves both to interact with the substrate for promoting photooxygenation and to deactivate singlet oxygen in the absence of substrate. The bifunctional photosensitizer prepared was subsequently applied in the asymmetric oxygenation of a series of β‐dicarbonyl compounds under green light irradiation. Control experiments and kinetic analyses were carried out to shed the light on the mechanism.
The electrochemical reduction of sensitive sulfonamides is described. The addition of a benzoyl group on the nitrogen atom facilitates the reductive cleavage of sulfonamides preventing β-fragmentation and epimerization. This strategy was successfully applied to the cyclopropylamine and to α-amino stannanes.
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