Synthesis of chromenes with isoprenoid side chains and their selective ozonolysis

The reactions of trimethylhydroquinone with isoprenoid allylic alcohols catalyzed by a Pentasil type zeolite in the H-form gave trimethyl-1,4-benzoquinones with the corresponding isoprenoid group, which were subsequently transformed into the target ³-chromenes on treatment with pyridine. Partial ozonolysis of chromenes proceeded selectively at the -bond of the side chain, resulting in the corresponding chromenes with an -carbonyl group.     

Direct palladium/carboxylic acid-catalyzed allylation of anilines with allylic alcohols in water

The direct activation of C-O bonds in allylic alcohols in water as a suspension medium by palladium complexes has been accelerated by carrying out the reactions in the presence of a carboxylic acid. The palladium-catalyzed allylation of anilines using allylic alcohols directly gave allylic anilines in good yields.     

FT-infrared band analysis and temperature programmed dessorption for the Y,L and ferrierite zeolites

With the aim to qualifying and quantifying the acidity of the Y, L and ferrierite zeolites, an infrared band analysis of pyridine adsorption and programmed temperature dessorption measurements were carried out to a set of nine samples of the Y, L and ferrierite zeolites. The infrared spectra before and after the pyridine adsorption process had revealed that the ferrierite zeolite shows, almost in the totality, Br?nsted acid sites. The Y and L zeolites present, also, significative concentrations of Br?nsted and Lewis acid sites. These facts allow to conclude that zeolite ferrierite is the strongest acid zeolite among these three types.     

Study of methanol and isobutanol coupling over acid catalysts

The coupling of methanol and isobutanol was carried out over selected acid catalysts. An amorphous silica-alumina, a zeolite and aluminas were tested as catalysts of the coupling. The correlation between the catalysts acidity and their activity and selectivity was studied. The catalytic tests were carried out in a fixed-bed flow microreactor working on line with a gas-chromatograph. The acidic properties of the catalysts were followed by IR studies of pyridine adsorption. The results obtained proved that the strength and the concentration of acid sites on the catalysts surface effected the alcohols conversion to ethers. It was found that the undesirable dehydration of isobutanol to isobutene was catalyzed by stronger acid sites than those required for the etherification reaction. This revised version was published online in June 2006 with corrections to the Cover Date.     

Palladium-catalyzed deracemization of allylic carbonates in water with formation of allylic alcohols: hydrogen carbonate ion as nucleophile in the palladium-catalyzed allylic substitution and kinetic resolution

The palladium-catalyzed deracemization of racemic cyclic and acyclic allylic methyl carbonates in water in the presence of N,N'-(1R,2R)-1,2-cyclohexanediylbis[2-(diphenylphophino)benzamide] proceeds with high enantioselectivities to give the corresponding allylic alcohols in high yields. This deracemization involves a palladium-catalyzed allylic substitution with the in-situ-formed hydrogen carbonate ion and an irreversible decomposition of the intermediate allylic hydrogen carbonates, with formation of the corresponding allylic alcohols. The palladium-catalyzed reaction of racemic cyclic allylic acetates with potassium hydrogen carbonate in water in the presence of the chiral bisphosphane proceeds with a highly selective kinetic resolution to give the corresponding allylic alcohols and allylic acetates.     

Catalytic asymmetric generation of (Z)-disubstituted allylic alcohols

A one-pot method for the direct preparation of enantioenriched (Z)-disubstituted allylic alcohols is introduced. Hydroboration of 1-halo-1-alkynes with dicyclohexylborane, reaction with t-BuLi, and transmetalation with dialkylzinc reagents generate (Z)-disubstituted vinylzinc intermediates. In situ reaction of these reagents with aldehydes in the presence of a catalyst derived from (-)-MIB generates (Z)-disubstituted allylic alcohols. It was found that the resulting allylic alcohols were racemic, most likely due to a rapid addition reaction promoted by LiX (X = Br and Cl). To suppress the LiX-promoted reaction, a series of inhibitors were screened. It was found that 20-30 mol % tetraethylethylenediamine inhibited LiCl without inhibiting the chiral zinc-based Lewis acid. In this fashion, (Z)-disubstituted allylic alcohols were obtained with up to 98% ee. The asymmetric (Z)-vinylation could be coupled with tandem diastereoselective epoxidation reactions to provide epoxy alcohols and allylic epoxy alcohols with up to three contiguous stereogenic centers, enabling the rapid construction of complex building blocks with high levels of enantio- and diastereoselectivity.     

H-MCM-22沸石分子筛中Brnsted/Lewis酸协同效应的~1H 和~(27)Al双量子魔角旋转固体核磁共振研究

采用各种固体核磁共振 (NMR) 技术详细研究了 H-MCM-22 分子筛中 Brnsted/Lewis 酸的协同效应. 二维 1H 双量子魔角旋转 (DQ-MAS) NMR 结果表明, 在脱铝 H-MCM-22 分子筛中 Brnsted 酸位 (骨架桥式羟基) 和 Lewis 酸位 (非骨架铝羟基) 之间是空间邻近的, 暗示着可能存在 B/L 酸协同效应. 二维 27Al DQ-MAS NMR 结果揭示了各种铝物种之间的空间邻近性, 表明 B/L 酸协同效应优先发生在 H-MCM-22 分子筛超笼中的骨架 T6 位铝和非骨架铝物种之间. 2-13C-丙酮探针分子实验发现, 因 B/L 酸协同效应而导致脱铝 H-MCM-22 分子筛酸性明显增强, 氘代吡啶探针分子实验也证实在 H-MCM-22 分子筛的超笼中发生了 B/L 酸协同效应. 上述结果将有助于我们理解在脱铝 H-MCM-22 分子筛上发生的多相催化机理.     

原位FTIR及探针反应法研究Pt与L沸石的相互作用

本文报道了一种适合催化研究的金属原位IR池,Pt分散在NH~4L沸石上呈缺电子性,在异丙醇分解反应中不显示脱氢活性,但通过加氢抗结炭作用保护着沸石上的酸位,从而增强了NH~4L沸石的酸性催化作用,负载在碱性KL沸石上的Pt呈富电子性,在反应中极易被噻吩中毒(Pt/KL+NH~4L)混合样品在预处理和反应的过程中Pt从KL 向NH~4L沸石上迁移,导致其催化性能相似于Pt/NH~4L,实验证明:Pt与L 沸石载体之间存在着明显的相互作用,由于Pt易给出电子而不易接受电子,因此与酸位的相互作用强于与碱位的相互作用.     

Direct palladium/carboxylic acid-catalyzed C-allylation of cyclic 1,3-diones with allylic alcohols in water

The direct activation of C-O bonds in allylic alcohols in water as a suspension medium by palladium complexes has been accelerated by carrying out the reactions in the presence of a carboxylic acid. The palladium-catalyzed allylation of cyclic 1,3-diones using allylic alcohols directly gave the corresponding C-allylated products in good yields.     

ZSM-5型分子筛的表面酸性与催化活性

合成了一批不同硅铝比的HZSM－5沸石分子筛，并用CO62 ,Fe^3 离子对其进行改性，测定了它们在醛氨缩合反应合成吡啶中的活性和选择性。对照它们的NH3－TPD，吡啶吸附红外光谱，研究了催化剂的表面酸性与醛氨缩合催化活性的关系。研究表明，硅铝比较小时，HZSM－5的酸中心较多，但过多的酸中心会引发其它的裂解反应和缩合反应，从而降低催化剂的活性和选择性；当硅铝比为120左右时，催化活性达到最大，吡啶碱产率达60％；若继续增大硅铝比，则无足够的酸中心进行反应，用Co^2 ,Fe^3 离子对HZSM进行改性，其B酸中心变化不明显，L酸中心减少，对氨气的吸附能力有所下降，从而保证了适当的酸中心暴露，有利于反应，采用CoZSM-5催化剂，吡啶碱产率可达78％。     

Preparation of stereodefined homoallylic amines from the reductive cross-coupling of allylic alcohols with imines

Regio-, diastereo-, and enantioselective coupling reactions between imines and allylic alcohols have been developed. These coupling reactions deliver complex homoallylic amine products through a convergent C-C bond forming process that does not proceed through intermediate allylic organometallic reagents. In general, convergent coupling, by exposure of an allylic alkoxide to a preformed Ti-imine complex, occurs with allylic transposition in a predictable and stereocontrolled manner. While simple diastereoselection in these reactions is high, delivering anti-products with ≥20:1 selectivity, the organometallic transformation described is compatible with a diverse range of functionality and substrates (including aliphatic and aromatic imines, allylic silanes, trisubstituted alkenes, vinyl- and aryl halides, trifluoromethyl groups, thioethers, and aromatic heterocycles). Alkene geometry of the products is a complex function of the allylic alcohol structure and is consistent with a mechanistic proposal based on syn-carbometalation followed by syn-elimination by way of a boat-like transition state geometry. Single asymmetric coupling reactions provide a means to translate the stereochemical information of the allylic alcohol to the homoallylic amine or to control diastereoselection in the coupling reactions of achiral allylic alcohols with chiral imines. Double asymmetric coupling reactions are also described that afford a unique means to control stereoselection in these complex convergent coupling processes. Finally, empirical models are proposed that are consistent with the observed stereochemical course of these coupling reactions en route to chiral homoallylic amines possessing di- or trisubstituted alkenes and anti- or syn- relative stereochemistry at the allylic and homoallylic positions.     

Dual Platinum and Pyrrolidine Catalysis in the Direct Alkylation of Allylic Alcohols: Selective Synthesis of Monoallylation Products

A dual platinum‐ and pyrrolidine‐catalyzed direct allylic alkylation of allylic alcohols with various active methylene compounds to produce products with high monoallylation selectivity was developed. The use of pyrrolidine and acetic acid was essential, not only for preventing undesirable side reactions, but also for obtaining high monoallylation selectivity.     

A novel acid-catalyzed C5-alkylation of oxindoles using alcohols

A novel C5-alkylation of oxindoles using alcohols as alkylating agents under acid catalysis is described for the first time. The reactions of various benzylic, allylic and propargylic alcohols are studied to obtain the corresponding 5-substituted oxindoles in good yields.     

介孔ZSM-5沸石微球催化剂上萘的苄基化反应

以有机硅烷化的二氧化硅为硅源,制备了由纳米粒子聚集而成的、具有晶间和晶内介孔的微球状ZSM-5(MMZ-5)沸石.通过吡啶(Py)和2,6-二叔丁基吡啶(DTBPy)在介孔沸石表面吸附的原位红外测试,对其酸性进行了表征.与微孔ZSM-5沸石相比,MMZ-5沸石上的Lewis酸位和总酸位增加,特别是探针大分子DTBPy(动力学直径约为1.05 nm)可及的Br?nsted酸位显著提高.萘在MMZ-5沸石上的苄基化催化结果表明,反应发生在拥有大量活性位的沸石外表面,大的沸石外表面为该催化反应提供了作用空间,从而提高了沸石活性位的有效利用率,使MMZ-5沸石上萘的苄基化反应活性显著提高,能够生成大分子产物一苄基萘和二苄基萘;其中,一苄基萘的选择性约为79%,且随着反应时间的延长,MMZ-5沸石大的晶内介孔(3-5 nm)为反应提供了有效反应空间,促进一苄基萘向二苄基萘转化.异构体α-一苄基萘和β-一苄基萘的摩尔比值约为83:17,该值不随着温度和转化率的变化而改变.     

亚硝胺在沸石上催化分解的研究

采用气相色谱 质谱（GC MSD）、程序升温表面反应（TPSR）和红外光谱（IR）技术研究吡咯烷亚硝胺（NPYR）和二甲基亚硝胺（NDMA）等亚硝胺在NaY、HY、NaZSM 5、HZSM 5等沸石上的催化分解,并剖析其产物分布,发现亚硝胺在Na＋型沸石上的裂解产物近似于热裂解,而在H＋型沸石上则发生了质子参与的催化裂解反应.     

Palladium-catalyzed reactions of hypophosphorous compounds with allenes, dienes, and allylic electrophiles: methodology for the synthesis of allylic h-phosphinates

Hypophosphorous compounds (MOP(O)H(2), M = H, R(3)NH) effectively participate in metal-catalyzed C-P bond-forming reactions with allenes, dienes, and activated allylic electrophiles under mild conditions. The catalytic system Pd(2)dba(3)/xantphos is crucial to avoid or minimize the competitive reductive transfer-hydrogenation pathway available to hypophosphorous acid derivatives. Further investigation into the allylation mechanism provided access to the analogy allylic acetate-allylic phosphinate, which then led to the development of a Pd-catalyzed rearrangement of preformed allylic phosphinates esters and, ultimately, to a catalytic dehydrative allylation of hypophosphorous acid with allylic alcohols. The reactions disclosed herein constitute efficient synthetic approaches, not only to prepare allylic H-phosphinic acids but also their esters via one-pot tandem processes. In addition, the potential of H-phosphinates as useful synthons for the preparation of other organophosphorus compounds is demonstrated.     

Cs/ZSM-35 分子筛催化甲缩醛和乙酸甲酯发生一步法羟醛缩合反应

丙烯酸及其酯是重要的化工原料, 广泛应用于涂料、粘结剂、纤维等领域, 目前工业上常采用丙烯两段氧化法进行制备. 然而该方法以石油基原料丙烯为源头, 采用 V/Mo/Bi 等金属催化剂, 不符合可持续发展理念, 且存在环境污染及氧气下产物易过度氧化等问题. 因此, 如何高效、安全、大规模工业化制备丙烯酸及其酯是研究者追求的目标. 以乙酸甲酯(MAc) 和甲醛为原料, 通过羟醛缩合一步制备丙烯酸及其酯是一条完全不同于丙烯氧化法的合成路径, 原料均可由煤基甲醇得到, 符合我国"富煤、贫油、少气"的基本能源结构, 且该方法碳原子利用率为 100%, 副产物仅为水, 属于绿色环保合成路径.羟醛缩合是典型的碳链增长反应, 可在酸性催化剂、碱性催化剂、以及酸碱双功能催化剂存在下发生. 碱性催化剂一般为负载型碱金属氧化物, 例如以 SiO2为载体的负载型 Na, K, Cs 氧化物催化剂等, 但都存在活性组分流失的问题, 进而导致催化剂的失活, 难以实现工业化. 酸碱双功能催化剂是目前研究的热点, 由于具有酸催化剂的高选择性和碱催化剂的高活性, 其反应性能要远优于单一酸性催化剂和单一碱性催化剂, 广大研究者对此进行了深入广泛的研究, 目前基本处于实验室阶段. 相对而言, 目前酸性催化剂上通过羟醛缩合反应制备丙烯酸及其酯的研究工作较少, 特别是以固体酸为催化剂进行乙酸甲酯和甲醛气固相反应研究非常少见.我们以甲缩醛为甲醛源, 创新性地采用固体硅铝分子筛为酸性催化剂, 催化甲缩醛 (DMM) 和 MAc 发生羟醛缩合反应来制备丙烯酸. 硅铝分子筛具有较高的活性, 可高效地催化羟醛缩合反应, 且由于分子筛催化剂具有很好的再生性能, 即使催化剂寿命较短, 也可采用流化床或移动床等反应器进行工业化, 因此存在良好的工业化前景. 为了进一步深入研究酸性位和碱性位各自对 DMM 和 MAc 羟醛缩合反应的影响, 本文以 HZSM-35 分子筛为载体, 采用浸渍法制备不同碱金属铯氧化物含量的催化剂, 利用氮气吸附/脱附方法和化学程序升温 (NH3-TPD) 方法对其孔结构和酸性质进行表征, 并进一步考察催化剂的性能. 结果表明, 微孔体积随着碱金属 Cs 负载量的增加而逐渐减小, 当 Cs 负载量增加至 10 wt% 时, 样品微孔体积从初始 0.105 cm3/g 降至 0.063 cm3/g. NH3-TPD 结果显示, 当 Cs 负载量为 1 wt%, 酸性催化剂载体上的强酸和弱酸活性位被大量碱性氧化物占据; 当负载量超过 5 wt% 时, 所有的酸性位均被覆盖. 随后考察负载不同碱金属含量分子筛的羟醛缩合反应性能, 发现碱金属氧化物的引入不利于羟醛缩合反应的进行, 这主要是由于作为甲醛源的 DMM 只有在酸中心上才能进行分解产生甲醛, 促使羟醛缩合反应顺利进行. 当采用 DMM 为甲醛源时, 体系中必须有酸性位存在. 同时得知, 分子筛 HZSM-35 中强酸和弱酸均是羟醛缩合反应的有效酸性位, 但强酸同时催化原料发生类甲醇制烯烃过程, 致使大量烃类副产物生成, 产生较重的积炭物种. 羟醛缩合反应在含有大量弱酸催化剂上 (如γ-Al2O3) 也可顺利进行, 且具有较高的活性和稳定性.     

From Biomass‐Derived Furans to Aromatics with Ethanol over Zeolite

We report a novel catalytic conversion of biomass‐derived furans and alcohols to aromatics over zeolite catalysts. Aromatics are formed via Diels–Alder cycloaddition with ethylene, which is produced in situ from ethanol dehydration. The use of liquid ethanol instead of gaseous ethylene, as the source of dienophile in this one‐pot synthesis, makes the aromatics production much simpler and renewable, circumventing the use of ethylene at high pressure. More importantly, both our experiments and theoretical studies demonstrate that the use of ethanol instead of ethylene, results in significantly higher rates and higher selectivity to aromatics, due to lower activation barriers over the solid acid sites. Synchrotron‐diffraction experiments and proton‐affinity calculations clearly suggest that a preferred protonation of ethanol over the furan is a key step facilitating the Diels–Alder and dehydration reactions in the acid sites of the zeolite.     

介孔ZSM-5沸石微球催化剂上萘的苄基化反应

以有机硅烷化的二氧化硅为硅源,制备了由纳米粒子聚集而成的、具有晶间和晶内介孔的微球状ZSM-5（MMZ-5）沸石. 通过吡啶（Py）和2,6-二叔丁基吡啶（DTBPy）在介孔沸石表面吸附的原位红外测试,对其酸性进行了表征. 与微孔ZSM-5 沸石相比,MMZ-5 沸石上的Lewis 酸位和总酸位增加,特别是探针大分子DTBPy（动力学直径约为1.05 nm）可及的Brönsted 酸位显著提高. 萘在MMZ-5沸石上的苄基化催化结果表明,反应发生在拥有大量活性位的沸石外表面,大的沸石外表面为该催化反应提供了作用空间,从而提高了沸石活性位的有效利用率,使MMZ-5 沸石上萘的苄基化反应活性显著提高,能够生成大分子产物一苄基萘和二苄基萘;其中,一苄基萘的选择性约为79%,且随着反应时间的延长,MMZ-5 沸石大的晶内介孔（3-5 nm）为反应提供了有效反应空间,促进一苄基萘向二苄基萘转化. 异构体α-一苄基萘和β-一苄基萘的摩尔比值约为83：17,该值不随着温度和转化率的变化而改变.     

Effect of thermal treatment conditions on the acid properties of zeolite Beta

The acid properties of zeolite Beta were studied by IR spectroscopy with the use of adsorbed NH₃ and CO probe molecules. It was found that the strength of the Brønsted acid sites (BASs) of zeolite Beta was the same as that of zeolite ZSM-5. Approximately a third of the total amount of BASs participated in the formation of hydrogen bonds at interdomain boundaries; thus, they were inaccessible to molecules larger than the ammonia molecule. The qualitative and quantitative compositions of acid sites in zeolite Beta can be regulated by changing the conditions of calcination of the initial zeolite form (temperature and/or gas atmosphere). Calcination under vacuum conditions afforded the highest acidity of the zeolite with respect to all types of acid sites. Calcination in a flow of air resulted in the lowest acidity of the sample, especially, with respect to the concentration of strong Lewis acid sites, because of the formation of an alumina phase. Calcination in an atmosphere of helium resulted in a decrease (as compared with a vacuum) in the rate of removal of the organic template decomposition products of the initial zeolite form from the channel volume. The resulting ethylene was mainly adsorbed at strong Lewis sites and converted into undesorbed condensation products.