Catalytic Asymmetric Conjugate Addition of 2-Methyl-3,5-dinitrobenzoates to Unsaturated Ketones.

Asymmetric catalytic vinylogous Michael addition of 2-methyl-3,5-dinitrobenzoates to unsaturated ketones catalyzed by chiral rhodium catalysts has been established. This strategy allowed the synthesis of a variety of optically pure compounds containing imidazole and 3,5-dinitrobenzene skeletons in 64-98% yields with 88-98% ee. The developed reaction not only represents highly asymmetric catalytic enantioselective vinylogous Michael addition employing 2-methyl-3,5-dinitrobenzoates as a building block but also enriches the chemistry of catalytic asymmetric vinylogous Michael addition of 2-methyl-3,5-dinitrobenzoates. Furthermore, the protocol showed obvious advantages in reaction activity and enantioselectivity. When the chiral rhodium catalyst was reduced to 0.06 mol %, the gram-level reaction was still achieved to provide the desired product with 95% ee.

The organocatalytic synthesis of perfluorophenylsulfides via the thiolation of trimethyl(perfluorophenyl)silanes and thiosulfonates.

The organic superbase t-Bu-P4-catalyzed direct thiolation of trimethyl(perfluorophenyl)silanes and thiosulfonates was developed. Yields of perfluorophenylsulfides of up to 97% under catalysis of 5 mol% t-Bu-P4 were achieved. This method was shown to provide an efficient way to construct the perfluorophenyl-sulfur bond under mild metal-free reaction conditions.

An N-heterocyclic carbene-catalyzed switchable reaction of 9-(trimethylsilyl)fluorene and aldehydes: chemoselective synthesis of dibenzofulvenes and fluorenyl alcohols.

An N-heterocyclic carbene-catalyzed synthesis of dibenzofulvenes and fluorenyl alcohols was developed. In the presence of 10 mol% NHC (1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) and 4 Å molecular sieves, 9-(trimethylsilyl)fluorene undergoes an olefination reaction with aldehydes to produce dibenzofulvenes in 43-99% yields. However, on reducing the NHC loading to 1 mol% and with the addition of water, 9-(trimethylsilyl)fluorene selectively undergoes nucleophilic addition with aldehydes to afford fluorenyl alcohols in 40-95% yields.

Direct Assembly of Polysubstituted Naphthalenes via a Tandem Reaction of Benzynes and α-Cyano-ß-methylenones.

A mild and transition-metal-free benzannulation reaction for the construction of the naphthalene skeleton has been described. Benzynes react with α-cyano-ß-alkylenones through a tandem nucleophilic addition/cyclization/aromatization process to afford polysubstituted naphthalenes in 50-94% yields.

N-Heterocyclic carbene-catalyzed diastereoselective synthesis of sulfenylated indanes via sulfa-Michael-Michael (aldol) cascade reactions.

N-Heterocyclic carbene (NHC)-catalyzed diastereoselective synthesis of multisubstituted sulfenylated indanes has been developed. In the presence of 1 mol% NHC, various thiols underwent the sulfa-Michael-Michael cascade reaction with benzenedi(enones) efficiently to form the carbon-sulfur bond and construct sulfenylated indanes in good to excellent yields with high diastereoselectivity. In addition, the NHC-catalyzed sulfa-Michael-aldol cascade reaction between o-formyl chalcone and thiols has also been demonstrated to afford sulfenylated indanes with a free hydroxyl group in moderate yields and good diastereoselectivity.

N-Heterocyclic carbene-catalyzed stereoselective construction of olefinic carbon-sulfur bonds via cross-coupling reaction of gem-difluoroalkenes and thiols.

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.

Asymmetric Desymmetrization of 1,3-Diketones via Intramolecular Benzoin Reaction.

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.

N-Heterocyclic Carbene-Catalyzed Diastereoselective Vinylogous Michael Addition Reaction of γ-Substituted Deconjugated Butenolides.

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, ß-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.

Diastereoselective synthesis of N-aryl tetrahydroquinolines and N-aryl indolines by the tandem reaction of arynes.

A tandem reaction of arynes with α- or ß-amino ketones has been revealed. Arynes react with ß-amino ketones through a cascade insertion-cyclization process to afford N-aryl tetrahydroquinolines in good yield with excellent anti-selectivity. Meanwhile, the coupling of arynes with α-amino ketones produces multisubstituted indolines in high yield with syn-selectivity. A quaternary carbon center can be constructed in this process, and the reaction can be easily scaled up.

NHCs catalyzed hydrophosphonylation of α-ketoesters and α-trifluoromethyl ketones.

N-Heterocyclic carbenes catalyzed hydrophosphonylation reaction of α-ketoesters and α-trifluoromethyl ketones was developed. Under the catalysis of 10 mol% IPr, α-ketoesters or α-trifluoromethyl ketones reacted with dialkyl phosphites to provide quaternary α-hydroxyphosphonates in good to excellent yield.

Anxiety and Depression Among Imaging Doctors in Post-COVID-19 Period.

To investigate the mental state of medical imaging staff in Shandong Province, China, who have been on the forefront of the COVID-19 epidemic during its late stage in China. Questionnaires designed to assess anxiety and depression were administered on-location, and 5331 complete results were collected. SPSS software was used for statistical descriptions and analysis. Rates of anxiety disorders and depression among medical imaging workers in Shandong Province, China, were 6.1% and 6.5%, respectively, higher than those of anxiety and depression in Chinese residents before the epidemic. The outbreak in Xinjiang, China; virus mutation in Japan; and spread of the epidemic due to occupational errors were the primary reported causes of anxiety and depression among image workers. Medical imaging workers showed evidence of psychological abnormalities during the late stage of the epidemic in China.

Synthesis of Benzo[ b]fluoranthenes and Spiroacridines from Fluorene-Derived Alkenes and N-Arylimines via a Tandem Reaction with Benzynes.

Two tandem processes involving the cycloaddition of benzynes have been developed for the synthesis of polyaromatic hydrocarbons. Benzynes react with fluorene-derived alkenes through a tandem Diels-Alder reaction/dehydrogenation process to afford benzo[ b]fluoranthenes in 35-87% yields. In addition, an unprecedented [2 + 2] cycloaddition/ring-opening sequence of benzynes and fluorene-derived N-arylimines provides facile access to spiroacridines in 38-79% yields.

N-Heterocyclic carbene-catalyzed sulfa-Michael addition of enals.

An efficient N-heterocyclic carbene (NHC) catalyzed sulfa-Michael addition (SMA) between enals and thiols has been developed. Under the catalysis of 10 mol% stable free carbene IPr and with 20 mol% hexafluoroisopropanol (HFIP) as an additive, enals react with a variety of thiols to afford the SMA adducts in 54-98% yields. In this process, the free carbene preferentially interacts with thiols through hydrogen-bonding and no NHC-catalyzed extended Umpolung transformations were observed.

N-Heterocyclic carbene-catalyzed formal cross-coupling reaction of α-haloenals with thiols: organocatalytic construction of sp2 carbon-sulfur bonds.

A novel N-heterocyclic carbene (NHC)-catalyzed formal cross-coupling reaction between α-haloenals and thiols was developed. In the presence of 5 mol% NHC precursors and 1.6 equiv. potassium carbonate, various thiols coupled with α-haloenals to produce α-thioenals in 53% to 91% yield and excellent Z-selectivity.