Palladium-catalyzed asymmetric carbene coupling en route to inherently chiral heptagon-containing polyarenes.

Developing facile and direct synthesis routes for enantioselective construction of cyclic π-conjugated molecules is crucial. However, originate chirality from the distorted structure around heptagon-containing polyarenes is largely overlooked, the enantioselective construction of all-carbon heptagon-containing polyarenes remains a challenge. Herein, we present a highly enantioselective synthesis route for fabricating all carbon heptagon-containing polyarenes via palladium-catalyzed carbene-based cross-coupling of benzyl bromides and N-arylsulfonylhydrazones. A wide range of nonplanar, saddle-shaped tribenzocycloheptene derivatives are efficiently prepared in high yields with excellent enantioselectivities using this approach. In addition, stereochemical stability experiments show that these saddle-shaped tribenzocycloheptene derivatives have high inversion barriers.

Tunably strained metallacycles enable modular differentiation of aza-arene C-H bonds.

The precise activation of C-H bonds will eventually provide chemists with transformative methods to access complex molecular architectures. Current approaches to selective C-H activation relying on directing groups are effective for the generation of five-membered, six-membered and even larger ring metallacycles but show narrow applicability to generate three- and four-membered rings bearing high ring strain. Furthermore, the identification of distinct small intermediates remains unsolved. Here, we developed a strategy to control the size of strained metallacycles in the rhodium-catalysed C-H activation of aza-arenes and applied this discovery to tunably incorporate the alkynes into their azine and benzene skeletons. By merging the rhodium catalyst with a bipyridine-type ligand, a three-membered metallacycle was obtained in the catalytic cycle, while utilizing an NHC ligand favours the generation of the four-membered metallacycle. The generality of this method was demonstrated with a range of aza-arenes, such as quinoline, benzo[f]quinolone, phenanthridine, 4,7-phenanthroline, 1,7-phenanthroline and acridine. Mechanistic studies revealed the origin of the ligand-controlled regiodivergence in the strained metallacycles.

A novel lipid droplets-targeting ratiometric fluorescence probe for hypochlorous acid in living cells.

Lipid droplets were found to be involved in many organism activities. Here, a lipid droplets-targeted near-infrared fluorescence probe (named XHZ) for ratiometric detection of endogenous hypochlorous acid/hypochlorite (HClO/ClO-) in living cells was developed, which was constructed by a coumarin moiety and a malononitrile derivative. XHZ could detect HClO/ClO- with high selectivity and sensitivity in a ratiometric manner based on FRET (Förster Resonance Energy Transfer) mechanism. The two well-resolved emission (470/672 nm) bands could ensure accurate detection of HClO/ClO- in vitro as well as in vivo. XHZ was successfully used for ratiometric fluorescence imaging of exogenous and endogenous HClO/ClO- in RAW264.7 cells. A good linear relationship between the fluorescence intensity ratios of the two emissions and HClO/ClO- concentrations from 0 to 40 µM was obtained. Importantly, XHZ could localize mainly in lipid droplets of RAW264.7 cells. To the best of our knowledge, XHZ is the first lipid droplets-targeted ratiometric fluorescence probe for HClO/ClO-.

A mitochondria-targeted fluorescence probe for ratiometric detection of endogenous hypochlorite in the living cells.

A mitochondria-targeted fluorescence probe (CPBT) for ratiometric detection of endogenous hypochlorite in the living cells was developed. CPBT could detect hypochlorite with high selectivity and sensitivity in a ratiometric manner based on FRET mechanism. In absence of hypochlorite, when CPBT was excited with absorption maximum wavelength of the donor moiety, it showed the emission of acceptor moiety because of FRET process. However, in the presence of hypochlorite, the reaction of CC double bond with hypochlorite interrupted the conjugation system resulting in the inhibition of FRET process and the emission of the donor moiety. The two well-resolved emission bands can ensure accurate detection of hypochlorite. A good linear relationship between the fluorescence intensity ratios of the two emissions and the ClO- concentrations in the range from 41.8 nM (detection limit) to 12.5 µM was established. Importantly, CPBT could localize mainly in the mitochondria of RAW264.7 cells. CPBT was successfully used to fluorescence ratiometric imaging of endogenous hypochlorite in RAW264.7 cells.