RESUMO
The reaction of common acyl-metal species (acyl anion) with aldehydes to furnish acyloins has received much less attention and specifically was restricted to using preformed stoichiometric acyl-metal reagents. Moreover, the (catalytic) enantioselective variants remain unexplored, and the asymmetric synthesis of chiral acyloins has met significant challenges in organic synthesis. Here, we uncover the highly enantioselective coupling of acid chlorides with α-bromobenzoates by nickel catalysis for producing enantioenriched protected α-hydroxy ketones (acyloins, >60 examples) with high enantioselectivities (up to 99% ee). The successful execution of this enantioselective coupling protocol enables the formation of a key ketyl radical from α-bromoalkyl benzoate in situ generated from corresponding aldehyde and acyl bromide, which finally is captured by chiral acyl-Ni species catalytically in situ formed from acyl chlorides, thus avoiding the use of preformed acyl-metal reagents. The synthetic utility of this chemistry is demonstrated in the downstream synthetic elaboration toward a diverse set of synthetically valuable chiral building blocks and biologically active compounds.
Assuntos
Cloretos , Níquel , Bromobenzoatos , Estereoisomerismo , Aldeídos/química , Metais/química , CatáliseRESUMO
A novel red-emitting fluorescent probe (DDNA) for cysteine has been rationally designed and synthesized, which exhibited a low limit of detection to Cys (0.26⯵M) as well as a favorable large stokes shift (λEm-λEx =â¯128â¯nm). This novel fluorophore (HDM), which features a large π-conjugation system and typical intramolecular charge transfer (ICT) process, has a long emission wavelength at 631â¯nm. Besides that, as a turn-on fluorescent probe, it shows high selectivity and sensitivity for Cys over other metal ions and amino acids including the similar structured homocysteine (Hcy) and glutathione (GSH). Finally, the probe DDNA was successfully applied to bioimage intracellular Cys in Hela cells with low cytotoxicity.