化学•材料最新文献

We have established an efficient ruthenium(II) and iodine anion cocatalyzed dihalogenation and cascade cyclization of internal alkyne-tethered cyclohexadienones, which stereoselectively afforded numerous dihalogenation products with a bioactive hydrobenzofuran skeleton in high yields under mild conditions. In this transformation, the reaction pathway was determined by the concentration of electrophilic iodine reagent, which also provided a strategy for control of the reaction selectivity. Furthermore, this method features the use of 1,2-dihaloroethane as the halogen source via iodine anion catalyst.

A novel copper-catalyzed cyclization/chalcogenation of o-alkynylphenols with epoxides and elemental S₈/Se was developed for the synthesis of a 3-chalcogen-benzofuran architecture in a domino process with no intermediate isolation or purification. Various sensitive functional groups were compatible at room temperature and furnished chalcogenation derivatives in moderate to good yields.

Enamines are difficult to prepare on the bench due to their instability, which results in side reactions, decompositions, poor yields, etc. Herein, we developed a simple and effective method for making bench-stable enamines using a very low amount of nickel catalyst loading. The deuterium exchange, competitive reaction, and radical clock experiment have all been found to favor the ionic mechanism of this alkene isomerization. Scale-up and [3 + 2] annulation reaction of enamines with activated cyclopropane to deliver cyclopentane derivatives have shown the value of this method in organic synthesis.

The Gewald reaction is a well-established one-pot method to access 2-aminothiophenes from carbonyl compounds, activated acetonitriles, and elemental sulfur. To elucidate the reaction's poorly understood mechanism, with regard to the decomposition of sulfur and polysulfide intermediates, we have performed a comprehensive computational study using density functional theory (DFT) calculations at the M06-2X (or ωB97X-D)/aug-cc-pV(T + d)Z/SMD(C₂H₅OH) level of theory. The results show that the reaction is initiated by a Knoevenagel-Cope condensation, followed by opening of the elemental sulfur, leading to polysulfide formation. The polysulfide intermediates can interconvert and decompose using various mechanisms including unimolecular cyclization, nucleophilic degradation, and scrambling. Protonation of the polysulfides changes their electrophilic behavior and provides a kinetically favorable pathway for their decomposition. This protonation-induced intermolecular degradation is feasible for polysulfides of all lengths, but unimolecular decomposition is kinetically favored for long polysulfides (≥6 sulfur atoms). None of the pathways provide any thermodynamic benefit due to the lack of resonance-stabilized leaving group, and a complex equilibrium of polysulfides of all lengths is expected in solution. Cyclization of the monosulfide with aromatization to the thiophene product is the only driving force behind the reaction, funneling all of the various intermediates into the observed product in a thermodynamically controlled process.

At elevated temperatures, a strained, cyclic meta-quaterphenylene acetylene undergoes an intramolecular cyclization reaction to form benz[e]indeno[1,2,3-hi]acephenanthrylene. This reaction represents an example of a Diels-Alder reaction at the 2-, 1-, 1'-, and 2'-positions of a biphenyl derivative, a region analogous to the bay regions of perylene and other periacenes. The reaction proceeds cleanly with high conversion. Kinetics studies of a methylated derivative reveal that the ΔG^‡ for the reaction is ∼40-41 kcal/mol, and computational models predict a similar value of G_rel for the transition state of a concerted [4 + 2]-cycloaddition.

A BF₃·OEt₂-catalyzed cascade cyclization reaction of vinyloxirane with coumarin is described, affording the benzocoumarin derivatives with moderate to excellent yields (72-92%). The reaction demonstrates exceptional substrate tolerance and has been extensively explored for its potential in drug development, including scale-up experiments, functional group transformations, and screening of the products for anticancer activity. Moreover, the reaction mechanism has been rigorously validated through intermediate trapping and control experiments. Additionally, this reaction represents the uncommon nonmetal catalyzed intermolecular cyclization of vinyloxiranes.

In this report, we demonstrate olefin transposition/isomerization reactions catalyzed by a series of N,N,N-pincer (1,3-bis(2-pyridylimino)isoindoline) Ru-hydride complexes. The protocol proceeds at room temperature for most substrates, achieving excellent yields, regioselectivity, and diastereoselectivity in short reaction times. The air-stable Ru-chloride derivatives of these complexes exhibit comparable reactivity enabling benchtop setup and synthetic versatility. Furthermore, we demonstrate the potential for one-pot cascade sequences of the products derived from the transposition reactions.

Darunavir is a potent HIV protease inhibitor that has been established as an effective tool in the fight against the progression of HIV/AIDS in the global community. The successful application of this drug has spurred the development of derivatives wherein strategic regions (e.g., P1, P1', P2, and P2') of the darunavir framework have been structurally modified. An alternate route for the synthesis of darunavir and three related P1 and P1' derivatives has been developed. This synthetic pathway involves the use of a Crimmins titanium tetrachloride-mediated oxazolidine-2-thione-guided asymmetric glycolate aldol addition reaction. The resultant aldol adduct introduces the P1 fragment of darunavir via an aldehyde. Transamidation with a selected amine (isobutylamine or 2-ethyl-1-butylamine) to cleave the auxiliary yields an amide wherein the P1' component is introduced. From this stage, the amide is reduced to the corresponding β-amino alcohol and the substrate is then bis-nosylated to introduce the requisite p-nitrobenzenesulfonamide component and activate the secondary alcohol for nucleophilic substitution. Treatment with sodium azide yielded the desired azides, and the deprotection of the p-methoxyphenoxy group is achieved with the use of ceric ammonium nitrate. Finally, hydrogenation to reduce both the aniline and azide functionalities with concurrent acylation yields darunavir and its derivatives.

A novel method for synthesizing substituted 4-chloroquinolines has been devised, utilizing a cascade reaction of N-aryl enaminones promoted by bis(trichloromethyl) carbonate (BTC) and triphenylphosphine oxide (TPPO). This approach features accessible starting materials, a broad substrate range, extensive functional group compatibility, gentle reaction conditions, and straightforward operation. Its versatility is evidenced by its facile scalability and suitability for late-stage derivatization. A plausible mechanism involving α-carbonylation, 6π-azaelectrocyclization, and dehydroxychlorination sequence is proposed.

The effect of Zn on Cd accumulation in rice varies under flooding and drainage conditions, and the underlying mechanism during uptake and transport from the soil to grains remains unclear. Isotope fractionation and gene expression were investigated using pot experiments under distinct water regimes and with Zn addition to gain a deeper understanding of the molecular effects of Zn on Cd uptake and transport in rice. The higher OsHMA2 expression but constitutively lower expression of zinc-regulated, iron-regulated transporter-like protein (ZIP) family genes in roots under the drainage regime than the flooding regime caused the enrichment of nonheavy Zn isotopes in the shoots relative to roots but minimally affected Cd isotopic fractionation. Drainage regime seem to exert a striking effect on the root-to-shoot translocation of Zn rather than Cd, and increased Zn transport via OsHMA2. The changes in expression patterns in response to Zn addition were similar to those observed upon switching from the flooding to drainage regime, except for OsNRAMP1 and OsNRAMP5. However, soil solution-to-rice plants and root-to-shoot fractionation toward light Zn isotopes with Zn addition (Δ⁶⁶Zn_{rice plant-soil solution} = -0.49 to -0.40‰, Δ⁶⁶Zn_shoot-root = -0.36 to -0.27‰) indicated that Zn transport occurred via nonspecific uptake pathways and OsHMA2, respectively. Accordingly, the less pronounced and minimally varied Cd isotope fractionation suggested that OsNRAMP5 and OsHMA2 are crucial for Cd uptake and root-to-shoot transport, respectively, facilitating Cd accumulation in grains. This study demonstrated that a high Zn supply promotes Cd uptake and root-to-shoot transport in rice by sharing distinct pathways, and by utilizing a non-Zn-sensitive pathway with a high affinity for Cd.