Yuhan Zhou

Ammonia formation by a thiolate-bridged diiron amide complex as a nitrogenase mimic

Although nitrogenase enzymes routinely convert molecular nitrogen into ammonia under ambient temperature and pressure, this reaction is currently carried out industrially using the Haber–Bosch process, which requires extreme temperatures and pressures to activate dinitrogen. Biological fixation occurs through dinitrogen and reduced NxHy species at multi-iron centres of compounds bearing sulfur ligands, but it is difficult to elucidate the mechanistic details and to obtain stable model intermediate complexes for further investigation. Metal-based synthetic models have been applied to reveal partial details, although most models involve a mononuclear system. Here, we report a diiron complex bridged by a bidentate thiolate ligand that can accommodate HN=NH. Following reductions and protonations, HN=NH is converted to NH3 through pivotal intermediate complexes bridged by N2H3– and NH2– species. Notably, the final ammonia release was effected with water as the proton source. Density functional theory calculations were carried out, and a pathway of biological nitrogen fixation is proposed. Although it is achieved routinely by nitrogenases, the conversion of molecular dinitrogen into ammonia under ambient conditions is proving difficult with synthetic systems. A thiolate-bridged diiron complex has now been developed that produces ammonia from coordinated N2H2 through a sequence of reduction and protonation reactions that may well mimic the biological nitrogen fixation.

Synthesis of trifluoromethyl ketones via tandem Claisen condensation and retro-Claisen C-C bond-cleavage reaction.

A highly efficient, operationally simple approach to trifluoromethyl ketones has been developed that builds on the use of a tandem process involving Claisen condensation and retro-Claisen C-C bond cleavage reaction. Enolizable alkyl phenyl ketones were found to react readily with ethyl trifuoroacetate under the promotion of NaH to afford trifluoroacetic ester/ketone exchange products, trifluoromethyl ketones, which were quite different from the general Claisen condensation products, β-diketones. This procedure uses readily available starting materials and can be extended to the preparation of perfluoroalkyl ketones in excellent yield.

Synthesis of 6-Trichloromethylphenanthridines by Transition Metal-Free Radical Cyclization of 2-Isocyanobiphenyls.

An efficient method for the synthesis of 6-trichloromethylphenanthridines by benzoyl peroxide promoted cyclization reaction of 2-isocyanobiphenyls with carbon tetrachloride is developed. A radical pathway is proposed and evidenced for the reaction mechanism. This reaction tolerates a wide range of functional groups and the resulting 6-trichloromethylphenanthridines can be utilized as a useful synthetic precursor for corresponding 6-substituted phenanthridines.

Mild and Highly Enantioselective Vinylogous Aldol Reaction of Brassard’s Diene with Aromatic Aldehydes by Combined Lewis Acid Catalyst

The combined Lewis acid catalytic system, generated from (R)-1,1-bi-2-naphthol [(R)-BINOL], Ti(O-i-Pr)(4), H(2)O, and lithium chloride, effectively catalyzed the enantioselective vinylogous aldol reaction of Brassards diene with aromatic aldehydes affording the (Z)-delta-hydroxyl-alpha,beta-unsaturated esters exclusively in good yields with excellent enantioselectivities (90-99% ee) under mild conditions. A Lewis acid-Lewis acid bifunctional working model was proposed for the catalytic process based on some control experiments.

Synthesis of gem-Difluoroallylboronates via FeCl2-Catalyzed Boration/β-Fluorine Elimination of Trifluoromethyl Alkenes

The first ferrous chloride catalyzed boration/β-fluorine elimination of trifluoromethyl alkenes is described. Thus, a full range of gem-difluoroallylboronates were obtained in high yield under mild conditions. As an important fluorinated building block, gem-difluoroallylboronate can be readily converted into diverse difluoro-substituted species.

Synthesis of (Z)-α-Trifluoromethyl Alkenyl Triflate: A Scaffold for Diverse Trifluoromethylated Species

An efficient method for the synthesis of (Z)-selective α-trifluoromethyl alkenyl triflates is described. As an important fluorinated building block, it is utilized successfully for the synthesis of various trifluoromethyl derivatives such as diarylethylenes, enynes, alkynes, and benzofurans.

Highly Enantio- and Diastereoselective Vinylogous Aldol Reaction by LiCl-Assisted BINOL–Titanium Species

The first highly enantio- and diastereoselective vinylogous aldol reaction between propionyl acetate-derived Brassards diene and aldehydes was accomplished by titanium-lithium combined Lewis acid, affording δ-hydroxy-γ-methyl-β-methoxy acrylates. This methodology was utilized in convenient and concise construction of the polypropionate moiety in cystothiazole A and melithiazole C.

Synthesis, structure and herbicidal activity of substituted phenyl pyrazole derivatives

To search for novel Protox inhibitors, a series of phenyl and 1,4-benzoxazin-5-yl pyrazole derivatives were synthesised from 3-(4-chloro-2-fluoro-5-methoxyphenyl)-1-methyl-5-trifluoromethyl-1H-pyrazole or its halogen substituted derivatives, via a serial of reactions that included nitration, reduction, acetylation, ring closure, methylation, etc. The single crystal of 2-(N-acetylacetamido)-6-chloro-3-[4-chloro-5-(trifluoromethyl)-1-methyl-1H-pyrazol-3-yl]-4-fluorophenyl acetate was prepared, and its structure was determined by X-ray analysis. The preliminary bioassay test shows that some of the compounds have high bioactivity. Especially, even at a low dosage of 150 g hm−2, 2-(N-acetylaceta-mido)-6-chloro-3-[4-chloro-5-(trifluoromethyl)-1-methyl-1H-pyrazol-3-yl]-4-fluorophenyl acetate exhibited high activity, the inhibiting rate for both of the weeds reached above 90%.

Iron-catalyzed boration of allylic alcohols with H3BO3 as an additive

ABSTRACT A method for the synthesis of allylboronates by iron-catalyzed boration of allylic alcohols with H3BO3 as an additive is developed. The introduction of H3BO3 promotes the cleavage of C‒O bond in allylic alcohols obviously. Functional groups, such as fluoro, chloro, bromo, alkyl, and alkoxy, are tolerated well. Thus, various allylboronates are obtained in acceptable yield. GRAPHICAL ABSTRACT

Base-Controlled Regiodivergent Azidation of Trifluoromethyl Alkenyl Triflates: Transition-Metal-Free Access to CF3-Containing Allyl Azides and Alkenyl Azides

A base-controlled regiodivergent azidation of trifluoromethyl alkenyl triflates providing either (E)-3-azido-1-aryl-4,4,4-trifluorobut-1-ene (CF3-containing allyl azides) or (Z)-1-azido-1-aryl-4,4,4-trifluorobut-1-ene (CF3-containing alkenyl azides) is described. Catalyzed by Et3N, the azidation of trifluoromethyl alkenyl triflates with TMSN3 gave CF3-containing allyl azides. On the other hand, using stoichiometric DBU, the regioisomeric azidation products, CF3-containing alkenyl azides, were obtained in good yield. A further transformation for CF3-containing amines, triazoles, and azirines highlights the practical applicability of this transition-metal-free protocol.