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991.
Treatment of N-tosylpyrroles or N-tosylindoles with α-unsubstituted α,β-unsaturated carboxylic acids or unsaturated carboxylic acids having an α electron-withdrawing substituent in the presence of TFAA and a Lewis acid catalyst resulted in the formation of fused cyclopentenones via a tandem acylation–Nazarov cyclization sequence, while either the acylation product obtained or no reaction occurred in the absence of the Lewis acid catalyst.  相似文献   
992.
The enantioselective reduction of prochiral ketones with NaBH4/Me2SO4/(S)-Me-CBS is described. Borane is generated in situ via the reaction of NaBH4 with Me2SO4 in tetrahydrofuran, which is as efficient as the commercial one. Such in situ–generated borane reagent was applied to reduce prochiral ketones in the presence of chiral oxazaborolidine catalyst directly. The corresponding chiral secondary alcohols were obtained with excellent enantiomeric excesses (93–99% ee) and good to excellent yield (80–99%).  相似文献   
993.
A new three-component cyclization method is described involving two starting materials, ethyl 4-chloroacetoacetate and aldehydes, catalyzed by piperidine, acid, and iodine. Ten corresponding polysubstituted phthalides are formed with good yields (44–78%). A mechanism of the reaction is also proposed.  相似文献   
994.
A parallel solid-phase synthesis of 2,4,5-trisubstituted thiophene-3-carbonitrile derivatives was developed. The polymer-supported synthetic route progressed using the sulfide linker via a traceless strategy. The initial synthesis utilized the Thorpe–Ziegler type cyclization of α-haloketone and polymer-supported 2,2-dicyanoethene-1,1-bis(thiolate), which was derived from the Merrifield resin. The resulting thiophene resin was introduced to one substitution by N-arylation. After oxidation of sulfides to sulfones in the thiophene resins for subsequent cleavage, nucleophilic desulfonative substitution with amines and thiols afforded the desired thiophene-3-carbonitrile derivatives in good overall yields.  相似文献   
995.
Novel fluorine-containing ultraviolet absorbers (FBPs) with low surface energy were successfully synthesized based on 2,4-dihydroxy benzophenone (BP-1), and their structures were characterized by 1H NMR, 13C NMR, FTIR, and HRMS. UV absorption of FBPs was studied in 10−4 M dichloromethane (CH2Cl2), which demonstrated the superior UV absorption capability of FBPs (ca. ?=1.7×104 to 2.2×104 at λmax) over the matrix (?=1.7×104 at λmax). Quantum chemistry calculation was performed to investigate the stable structure and UV electronic absorption bands of FBPs. The surface chemistry information of high-chlorinated polyethylene (HCPE) coating films embedded with ultraviolet absorbers (UVAs) was given by X-ray photoelectron spectroscopy (XPS) and contact angle measurement. The results show that the surface enrichment capability of FBPs is remarkably better than traditional UVAs (including BP-1, BP-3, BP-12) because of the low surface energy properties of FBPs.  相似文献   
996.
The dinuclear zinc–ProPhenol complex is applied as efficient catalyst in the highly stereoselective tandem Michael addition/acetalization reactions of cyclic 1,3-diketones and β,γ-unsaturated α-ketoesters. A variety of substrates are well-tolerated, and a broad range of synthetically and pharmaceutically useful chiral chromene derivatives are directly produced in good yields of up to 96% and good enantioselectivities of up to 96% ee.  相似文献   
997.
To discover novel nucleosides as potential antiviral agents, 2′-spirolactam and 2′-spiropyrrolidine-containing nucleoside analogs were envisioned. Efficient synthetic routes were developed with an epoxide opening as the key step to establish the quaternary center at the 2′ position, leading to the design and synthesis of uridine analogs 8 and 21, prodrugs 1316, and cytidine analog 11.  相似文献   
998.
2H-1,2,3-Triazoles (2) were synthesized by [3+2] cycloaddition of (Z)-2,3-diaryl substituted acrylonitriles (1) with sodium azide and ammonium chloride in DMF/water. This method represents a facile and efficient reaction procedure for the synthesis of 4,5-diaryl-2H-1,2,3-triazoles in modest to good yields.  相似文献   
999.
McbA was characterized in vitro as a novel amide synthetase in the marinacarbolines A–D biosynthetic pathway, catalyzing amide bond formation between 1-acetyl-3-carboxy-β-carboline (1a) and substituted-β-phenethylamines (1b, 2b, 3b) and tryptamine (4b) in an ATP-dependent manner. Enzyme kinetic analyses highlight β-phenethylamine as the most suitable amine donor. McbA showed broad substrate compatibility with substituted amines; 10 new β-carboline analogues were chemoenzymatically generated.  相似文献   
1000.
Polyoxometalates K7[α-PW11O39]·14H2O (PW11) modified mesoporous silica (MCM-48) with cubic structure, was prepared by impregnation and calcination methods. The modified mesoporous silica sorbent (PW11/MCM-48) was studied as a potential adsorbent for U(VI) from aqueous solutions. MCM-48 and PW11/MCM-48 were confirmed by X-ray diffraction and nitrogen physisorption techniques. The results indicate the original keggin structure of PW11 and mesoporous structure of MCM-48 are maintained after supporting PW11 on mesoporous silica MCM-48. The effects of contact time, solid-to-liquid ratio (m/V), solution pH and ionic strength on U(VI) sorption behaviors of the pure and modified mesoporous silicas were also studied. Typical sorption isotherms such as Langmuir and Freundlich isotherms were determined for sorption process. The results suggest that the sorption of U(VI) on MCM-48 or PW11/MCM-48 are strongly dependent on pH values but independent of ionic strength. The sorption capacity of PW11/MCM-48 for U(VI) is about ten times more than that of MCM-48.  相似文献   
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