A novel organocatalytic olefinic carbon–sulfur bond forming reaction was developed. Under the catalysis of 10 mol% stable N-heterocyclic carbene, thiols undergo direct nucleophilic substitution reaction with gem-difluoroalkenes to produce α-fluorovinyl thioethers in high yields with excellent Z-selectivity. In this process, bases are not necessary.

N-Heterocyclic carbenes (NHCs) have been employed as highly efficient organocatalysts for fluorinated silyl-Reformatsky reaction of carbonyl compounds. In the presence of 5–10 mol % NHC A, various aldehydes and 2,2,2–trifluoroacetophenone reacted with difluoro (trimethylsilyl) acetate to produce β–hydroxy gem–difluoro esters in 20–96% yields.N-heterocyclic carbene-catalyzed fluorinated silyl-Reformatsky reaction of aldehydes and difluoro (trimethylsilyl) acetate.Download high-res image (138KB)Download full-size image

Tetraphenylethylene (TPE) is known for its aggregation-induced emission enhancement (AIEE) effect due to the restriction of intramolecular rotation. Some halogen-substituted fluorophores show interesting luminescent phenomena via C–H⋯halogen interactions. By combining TPE units, a halogen with a difluoroboron β-diketonate fluorophore, three complexes, 2a, 2b and 2c, were designed and synthesized. All of them exhibited intramolecular charge transfer, high fluorescence quantum yields, AIEE characteristics and high-contrast mechanochromism. By either grinding-fuming or grinding–annealing cycles, the pristine state or the original emission color of the three complexes can be almost recovered reversibly. In particular, 2c exhibits spontaneous reversibility after grinding at room temperature. Owing to the effect of halogen (Cl, Br), 2b and 2c show polymorphism-dependent fluorescence (yellow plate-like crystals and green needlelike crystals) and higher contrast than 2a before/after grinding. The maximum fluorescence emission wavelength of 2b and 2c shifts bathochromically 70 nm and 59 nm after grinding, respectively. To reveal the mechanochromic mechanism, a series of tests including powder XRD, fluorescence lifetime, DSC, and solid state UV-visible absorbance were completed. The results indicate that mechanochromism of the complexes can be correlated with the transformation between the amorphous and the crystalline states and metastable state formation after grinding, rather than molecular planarization, excimer or exciplex formation. To the best of our knowledge, this is the first example of no alkyl- or alkoxy-substituted difluoroboron β-diketonate complexes that exhibit reversible mechanochromic luminescence.

N-heterocyclic carbenes (NHCs) have been utilised as highly efficient organocatalysts to catalyse Peterson olefination reaction of aldehydes with trimethylsilylketene ethyl trimethylsilyl acetal or fluoro(trimethylsilyl)ketene ethyl trimethylsilyl acetal to produce the corresponding functionalized olefines in 34–93% yields with excellent stereoselectivities.

A general method for the asymmetric desymmetrization of 1,3-diketone substrates via chiral N-heterocyclic carbene catalyzed intramolecular benzoin reactions was developed. Five- and six-membered cyclic ketones bearing two contiguous fully substituted stereocenters were generated with excellent diastereoselectivities and moderate to excellent enantioselectivities.

An efficient N-heterocyclic carbene (NHC)-catalyzed vinylogous Michael addition of deconjugated butenolides was developed. In the presence of 5 mol % of the NHC catalyst, both γ-alkyl- and aryl-substituted deconjugated butenolides undergo vinylogous Michael addition with various α, β-unsaturated ketones, esters, or nitriles to afford γ,γ-disubstituted butenolides containing adjacent quaternary and tertiary carbon centers in good to excellent yields with excellent diastereoselectivities. In this process, the free carbene is assumed to act as a strong Brønsted base to promote the conjugate addition.

A novel amide bond formation reaction was developed via N-heterocyclic carbene (NHC)-catalysed direct amidation of vinyl esters. In the presence of 5.0 mol % NHC catalyst, a variety of aromatic amines undergo acylation reaction with different vinyl esters to produce amides in 51% to quantitative yields.

N-Heterocyclic carbenes (NHCs) have been served as efficient catalysts for cyanomethylation of carbonyl compounds. In the presence of 5 mol % NHC, various aldehydes and 2,2,2-trifluoroacetophenone reacted with trimethylsilylacetonitrile (TMSAN) to give β-hydroxynitriles in moderate to high yields.

An organocatalytic protocol for the synthesis of dimethyl carbonate has been developed. Under the catalysis of 5 mol% N-heterocyclic carbenes, ethylene carbonate undergoes transesterification reaction with methanol under very mild reaction conditions, producing dimethyl carbonate with high efficiency. Furthermore, this N-heterocyclic carbene promoted transesterification can be scaled-up easily without lose of the conversion of dimethyl carbonate.

A novel organocatalytic olefinic carbon–sulfur bond forming reaction was developed. Under the catalysis of 10 mol% stable N-heterocyclic carbene, thiols undergo direct nucleophilic substitution reaction with gem-difluoroalkenes to produce α-fluorovinyl thioethers in high yields with excellent Z-selectivity. In this process, bases are not necessary.