The biological properties of trifluoromethyl compounds have led to their ubiquity in pharmaceuticals, yet their chemical properties have made their preparation a substantial challenge, necessitating innovative chemical solutions. We report the serendipitous discovery of a borane-catalyzed formal C(sp3)-CF3 reductive elimination from Au(III) that accesses these compounds by a distinct mechanism proceeding via fluoride abstraction, migratory insertion, and C-F reductive elimination to achieve a net C-C bond construction. The parent bis(trifluoromethyl)Au(III) complexes tolerate a surprising breadth of synthetic protocols, enabling the synthesis of complex organic derivatives without cleavage of the Au-C bond. This feature, combined with the “fluoride-rebound” mechanism, was translated into a protocol for the synthesis of 18F-radiolabeled aliphatic CF3-containing compounds, enabling the preparation of potential tracers for use in positron emission tomography.
Reversible photocontrol of glycosides and glycoconjugates structures is a very attractive approach to modulate, in a spatiotemporal way, the various properties and biological activities of carbohydrates. We have synthesized three new azobenzene‐derived glycomacrolactones from thioglycopyranosides. The synthesized cyclic glycoazobenzenes can be reversibly photoisomerized between E and Z isomers with high fatigue resistance. A 1H NMR spectroscopic study shows that E → Z isomerization of glycomacrocycles induces large conformational change of the macrocyclic structures, without changing sugar 4C1 chair conformation. The Z‐glycoazobenzenes can be thermally converted back to the E‐isomers. Interestingly, these 16 to 17‐membered Z‐glycomacrolactones display higher thermal stability than the reported macrocyclic azobenzenes, the half‐life varying from 37 to 72 days. The excellent photoswitching property and bistability of the synthesized glycoazobenzenes open a new opportunity for the convergent synthesis of diastereomers of glycomacrocycles. Furthermore, chiroptical properties have been observed for both E and Z glycomacrolactones. The geometry of different isomers of macrocycles has been optimized with DFT calculations. Theoretical CD spectra obtained by TD‐DFT suggest that the E and Z glycomacrocycles adopt preferentially (P) helical structure for the azobenzene moiety.
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