Catalytic Reductive Carbene Transfer Reactions

Computational Insights into the Photoinduced Dimeric Gold-Catalyzed Divergent Dechloroalkylation of gem-Dichloroalkanes with Alkenes

The employment of dinuclear Au(I) catalysts in photomediated modern organic transformations has attracted significant attention over the past decade, which commonly demonstrates unique catalytic performance compared with the corresponding mononuclear gold complexes. Nevertheless, detailed mechanisms of dinuclear gold catalysis remain ambiguous, and further mechanistic understanding is highly desirable. Herein, computational studies were carried out to gain mechanistic insights into the photoinduced dinuclear gold-catalyzed divergent dechloroalkylation of gem-dichloroalkanes. Computational results suggest that a proton transfer from the additive, Hantzsch ester (HE), to the base, guanidine, could lead to an ionic pair complex, which is ready to undergo excitation under blue light irradiation to result in the corresponding triplet excited state. Then, the excited complex might undergo oxidative quenching with the dinuclear gold photocatalyst [AuI-AuI]2+, via a single-electron-transfer (SET) step to afford an unusual [Au1/2-Au1/2]+ dinuclear species. The corresponding mononuclear gold catalyst, [AuI]+, however, is not ready to enable the analogous step to give a [Au0] species, which might account for the unique characteristics of dinuclear gold catalysis. Subsequently, the formed [Au1/2-Au1/2]+ intermediate could trigger a Cl-atom transfer from dichloromethane in an inner-sphere manner to furnish a critical chloromethyl radical. Next, the resulting chloromethyl radical could attack the alkenyl moiety of substrates to generate the corresponding alkyl radicals. Then, three possible mechanistic pathways were explored to rationalize the substrate-dependent divergent transformations in this protocol. The main factors responsible for the diversified transformations were discussed.

Light induced diversity-oriented synthesis (DOS) library of annulated indolizine fluorophores for imaging non-lysosomal lipid droplets (LDs)

We report the design, synthesis, and biological evaluation of a novel class of annulated indolizines as fluorescent probes. The compounds were generated through an eco-friendly, blue LED-induced domino reaction in ethyl acetate. A library of 24 coloured compounds exhibited tuneable emissions. One of the compounds (which we call DASS-fluor) proved to be an excellent polarity sensing probe. It is biocompatible, photostable, and detects specific types of lipid droplets (LDs in response to oleic acid, stress, and drug-induced autophagy in lungs and hepatic carcinoma cells). In comparison to Nile Red (a commercial probe), DASS-fluor can differentiate non-lysosomal LDs from lysosomal LDs and offers an advantage in precisely mapping drug-induced lipidosis caused by increased non-lysosomal LDs in cancerous cells. This unique probe could be a potential fluorescent marker for specific types of lipidosis induced by drugs.