Synthesis and structural characterization of three copper coordination polymers with pyridine derivatives from hydro(solvo)thermal in situ decarboxylation reactions of 2,5-dicarboxylpyridine

The hydro(solvo)thermal self-assembles of CuI, KI and 2,5-dicarboxylpyridine [2,5-(COOH)₂py] in different molar ratios in H₂O/alcohol solutions produced three Cu coordination polymers as 2-D [N-C₂H₅py][Cu₃I₄] 1, 1-D [N-CH₃py][Cu₂I₃] 2 as well as 1-D [Cu(2-COOpy)₂]H₂O 3 (N-C₂H₅py=N-ethylpyridine, N-CH₃py=N-methylpyridine, 2-COOpy=2-carboxylpyridine). N-C₂H₅py in 1 and N-CH₃py in 2 derived from the solvothermal in situ simultaneous decarboxylation and N-alkylation reactions of 2,5-(COOH)₂py. The semi-decarboxylation reaction of 2,5-(COOH)₂py into 2-COOpy occurred in the preparation of 3. X-ray single-crystal analysis revealed that CuI is transformed into a 2-D [Cu₃I₄]⁻ layer in compound 1 and a 1-D chain in compound 2, templated by [N-C₂H₅py]⁺ and [N-CH₃py]⁺, respectively. Compound 3 is a divalent Cu compound. The Cu(II) centers with a 4+2 geometry are coordinated by μ₃-mode 2-COOpy ligands. All of the title compounds were characterized by CHN analysis, IR spectrum analysis and TG analysis. Compounds 1 and 2 exhibit fluorescence properties with the maximum emissions at 581 nm for 1 and 537 nm for 2.     

Tandem SN2-Michael addition to vinylogous carbonates for the stereoselective construction of 2,3,3,5-tetrasubstituted tetrahydrofurans

A stereoselective method for the synthesis of substituted tetrahydrofuran derivatives employing a tandem alkylation-Michael addition sequence to vinylogous carbonates is developed. The method could be used to synthesize THFs bearing tertiary ethers. Further, the method is extended to the synthesis of adjacent bis-THFs.     

Fe(II)-catalyzed N-alkylation of sulfonamides with benzylic alcohols

The FeCl₂/K₂CO₃ catalyst system was developed successfully for the N-alkylation of sulfonamides with benzylic alcohols via borrowing hydrogen method. XPS analysis suggested a possible catalyst cycle between Fe(II) and Fe(0). Under the optimized condition, the scope of the protocol was demonstrated in 21 different alkylation reactions. High yields, in general >90%, are achieved in most cases.     

A simple route towards peptide analogues containing substituted (S)- or (R)-tryptophans

We investigated the Lewis acid-promoted Friedel-Crafts alkylation of indole and substituted indoles with dehydroalanine-containing dipeptides R-Xaa-Dha-OR¹. The reaction proceeded with modest to sufficient diastereoselectivity, and yields strongly varied depending on the Lewis acid selected. The substituent R¹ of the ester group revealed some impact on the preferential formation of (S)-Trp or (R)-Trp. We exploited the reaction to prepare different peptides containing substituted tryptophans. To test the efficacy of this method for preparing biologically relevant compounds, we synthesized two unprecedented analogues of endomorphin-1, the endogenous agonist of the μ-opioid receptor, having either (S)- or (R)-2-methyltryptophan in position 3.     

Enantioselective alkylation of lactams and lactones via lithium enolate formation using a chiral tetradentate lithium amide in the presence of lithium bromide

Enantioselective alkylation of lactams and lactones can be realized up to 98% ee by deprotonation with a chiral tetradentate lithium amide (4b) in the presence of lithium bromide, and subsequent alkylation with active alkylating agents in non-chelating solvents.     

Friedel–Crafts alkylation reactions in pyridinium-based ionic liquids

The Friedel–Crafts alkylations of benzene in pyridinium-based ionic liquids (ILs) were investigated. The effects of catalyst–IL composition, reactant composition, quantity of catalyst and reaction temperature on this reaction were studied. The reactions were found to proceed under mild conditions with conversion; a simple product isolation procedure was achieved. The ILs rendered this reaction green characteristics. The ILs could also be recycled and reused as opposed to traditional solvent–catalyst systems.     

SO42-/ZrO2-TiO2催化苯与1-十二烯烷基化合成十二烷基苯

利用沉淀-浸渍法制备了SO42-/ZrO2-TiO2固体酸催化剂,优化了SO42-/ZrO2-TiO2催化苯与1-十二烯烷基化合成十二烷基苯的工艺条件,并通过IR及GC/MS对产物的结构进行了表征.结果表明: SO42-/ZrO2-TiO2对苯与1-十二烯的烷基化反应具有良好的催化性能,其催化中心主要为B酸中心.0.12g催化剂/ mL1-十二烯、n(苯)/n(烯)=6:1、反应时间3 h等优化条件下1-十二烯转化率100%,LAB与2-LAB选择性分别达到90.3%和88.6%.使用后的催化剂可以通过H2SO4浸渍500 ℃焙烧再生.GC/MS分析表明产物主要包括2～6-LAB及少量二烷基苯.     

脱铝MCM-49分子筛的结构、酸性及苯与丙烯液相烷基化催化性能研究

采用硝酸回流和水蒸气两种处理方法对用动态水热法合成的纳米MCM-49分子筛进行脱铝改性. 用XRD、氮气吸附-脱附、NH3-TPD、FTIR和NMR等技术进行了表征, 并考察了脱铝前后MCM-49分子筛在苯与丙烯液相烷基化反应中的催化性能. 27Al核磁共振谱表明, 硝酸回流和水蒸气处理能有效地脱除MCM-49分子筛的部分骨架铝和非骨架铝. NH3-TPD和FTIR表征结果表明, 脱铝降低了MCM-49分子筛的Brönsted酸和Lewis酸的酸量. 硝酸脱铝未改变分子筛的酸强度分布, 而在600 ℃水蒸气脱铝则造成酸强度的降低. 实验条件下, MCM-49分子筛的丙烯转化率为99.5%, 异丙苯的选择性为73.6%. 脱铝改性降低了烷基化反应活性和异丙苯的选择性, 提高了收率. 与脱铝前MCM-49分子筛相比, 常温下经硝酸处理5 h的脱铝MCM-49分子筛在保持催化活性相当的情况下, 异丙苯收率提高了5.3%.     

Large scale enantiomeric synthesis, purification, and characterization of ω-unsaturated amino acids via a Gly-Ni(II)-BPB-complex

The enantiomeric syntheses of ω-unsaturated amino acids and β-substituted ω-unsaturated amino acids were accomplished by using Gly-Ni-2[N-(N′-benzylprolyl)amino]benzophenone (BPB) as a chiral auxiliary. The synthesis provides excellent yields and high diastereoselectivities. The product crystallization followed by isomer epimerization strategy makes the reaction practical and useful for large-scale preparations. Dialkylation of the Ni(II)-complex, which was designed for mechanistic considerations, revealed that high diastereoselectivity is obtained due to the thermodynamic conformational stability of the Ni(II)-complex. The assignment of absolute configuration was accomplished by NMR, which is supported by corresponding X-ray structure and optical rotation data. Both enantiomerically pure amino acids can be synthesized in this alkylation-hydrolysis two-step strategy in multi gram scales.     

Influence of the metal and chiral diamine on metal(II)salen catalysed, asymmetric synthesis of α-methyl α-amino acids

The influence of the metal ion and chiral diamine used to form a metal(salen) complex on the catalytic activity of the complex in the asymmetric benzylation of an alanine enolate was investigated. Only metal ions which could form square-planar complexes gave catalytically active complexes, and best results were obtained with metal ions from the first row of transition metals, particularly copper(II) and cobalt(II). Salen ligands derived from acyclic, chiral 1,2-diamines were found to generate poor catalysts, an effect which seems to correlate with the ability of the substituents within the diamine to adopt a conformation in which they are anti to one another. Complexes derived from a variety of 5- and 6-membered cyclic 1,2-diamines did form active catalysts, but the enantioselectivity was always far lower than that of the parent cyclohexane-1,2-diamine derived complex.