分子筛催化苯甲醛与醇缩合反应的研究

1　引言分子筛作为催化剂由于其特殊的酸性和择形性在精细有机合成中获得了广泛的应用[1],在缩醛化反应中也表现出了良好的催化性能,如Joshi[2]等用HY和HZSM5分子筛作催化剂,将苯甲醛与甲醇缩合,获得了83%的苯甲缩甲醛,并考察了不同种类的醛在HZSM5分子筛上的择形性。王存...     

Acetalization of Carbonyl Compounds as Pentaerythritol Diacetals and Diketals in the Presence of Cellulose Sulfuric Acid as an Efficient,Biodegradable and Reusable Catalyst

This paper reports a practical and green method for the acetalization of carbonyl compounds as pentaerythritol diacetals and diketals derivatives using cellulose sulfuric acid as a biodegradable and reusable solid acid catalyst under thermal solvent‐free conditions.     

Phosphorylated Polyacrylonitrile Fibers as an Efficient and Greener Acetalization Catalyst

A novel solid acid catalyst (PAN_EAPF) is developed by immobilization of phosphoric acid on polyacrylonitrile fiber through covalent bonding. Various characterization techniques such as elemental analysis (EA), X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), etc. are utilized to confirm the successful grafting and the stability of the fiber catalysts during application. PAN_EAPF shows high catalytic activity in the acetalization of aldehydes owing to the high utilization efficiency of its functionalized acid sites. In addition, the strong polarity micro‐environment in the surface layers of PAN_EAPF make it highly suitable for catalytic application in both water and alcohol. Furthermore, the fiber catalyst can be applied to the acetalization of aldehydes in a continuous‐flow process at room temperature, and shows excellent reactivity and superior recyclability (over 20 times). The many advantages of PAN_EAPF such as simple preparation, convenient regulation of acid amount, high durability, and eco‐friendly process make it very attractive for fixed‐bed reactors in the chemical industry.     

A symmetry-based approach to the heterobicyclic core of the zaragozic acids—model studies in the C2-symmetric series

A conceptually novel access to models for the title structures has been achieved by rapid enantioselective construction of polyhydroxy diketones in a two-directional or convergent fashion and group-selective intramolecular acetalization.     

Studies on the Selective Reduction of the Amide Link of Acyclic and Macrocyclic Amidoketals: Unexpected Cleavage and trans‐Acetalization with Red‐Al®

Selective reduction of the amide moiety of acyclic and macrocyclic amidoketals was studied in presence of various reagents (BH₃ · Me₂S, iBuAlH₂, Red‐Al^®, LiAlH₄). The best results were obtained with lithium aluminium hydride in the presence of triethylamine traces, whereas borane dimethyl sulfide gave rise to a partial ketal reduction of the acyclic compound and Red‐Al^® to a cleavage of the macrocyclic molecule accompanied by an unexpected trans‐acetalization.     

大茴香醛改性海藻酸钠凝胶的制备及释药性能

在酸催化下使海藻酸钠与对甲氧基苯甲醛(又名大茴香醛)发生缩醛化反应,使其疏水改性,并将其制备成凝胶。利用红外(FTIR)、荧光、透射电镜(TEM)、扫描电镜(SEM)、紫外、热重分析(TGA)对产物进行了表征。结果表明,大茴香醛成功地与海藻酸钠发生了反应。该凝胶可以作为药物载体对牛血清白蛋白进行包埋释放,结果发现,改性后的产物其载药率和缓释性能比未改性的海藻酸钠有了一定的提高。     

SO_4~(2-)/SnO_2/SBA-15固体酸催化剂的制备及其在环酮缩合反应中的应用

采用等体积浸渍法制备了不同负载量的固体酸催化剂SO42-/SnO2/SBA-15,利用X射线粉末衍射、N2吸附-脱附和透射电镜等手段对样品进行了表征,并考察了催化剂对4-叔丁基环己酮与乙二醇缩合反应的催化性能.结果表明,SO42-/SnO2催化剂负载于SBA-15后其催化性能明显改善.研究了SO42-/20%SnO2/SBA-15催化剂上部分酮类化合物与乙二醇及1,2-丙二醇的缩合反应,并考察了反应时间和催化剂用量等因素对反应性能的影响.在适宜的温和条件下,一些环酮类底物如环己酮、4-甲基环己酮和4-叔丁基环己酮等均可反应得到相应的缩醛化产物,且催化剂至少可循环使用4次.     

Enantioselective Acetalization by Dynamic Kinetic Resolution for the Synthesis of γ‐Alkoxybutenolides by Thiourea/Quaternary Ammonium Salt Catalysts: Application to Strigolactones

Although acetalization is a fundamental transformation in organic synthesis, intermolecular asymmetric acetalization remains an unsolved problem. In this study, a thiourea‐ammonium hybrid catalyst was shown to promote the O‐alkylation of enols with a racemic γ‐chlorobutenolide through dynamic kinetic resolution to give chiral acetals with good enantioselectivity. The catalyst simultaneously activates both the nucleophile and electrophile in a multifunctional manner. This method was applied to the asymmetric synthesis of several strigolactones. DFT calculations suggest that hydrogen‐bonding interactions between the chlorine atom of the γ‐chlorobutenolide and the tosylamide hydrogen atom of the catalyst, as well as other types of noncovalent catalyst–substrate interactions, are crucial for achieving high stereoselectivity.     

Enantioselective Acetalization by Dynamic Kinetic Resolution for the Synthesis of γ-Alkoxybutenolides by Thiourea/Quaternary Ammonium Salt Catalysts: Application to Strigolactones

Although acetalization is a fundamental transformation in organic synthesis, intermolecular asymmetric acetalization remains an unsolved problem. In this study, a thiourea-ammonium hybrid catalyst was shown to promote the O-alkylation of enols with a racemic γ-chlorobutenolide through dynamic kinetic resolution to give chiral acetals with good enantioselectivity. The catalyst simultaneously activates both the nucleophile and electrophile in a multifunctional manner. This method was applied to the asymmetric synthesis of several strigolactones. DFT calculations suggest that hydrogen-bonding interactions between the chlorine atom of the γ-chlorobutenolide and the tosylamide hydrogen atom of the catalyst, as well as other types of noncovalent catalyst–substrate interactions, are crucial for achieving high stereoselectivity.     

Facile Method for Stereoselective Synthesis of New Chiral (1R,4aR,8aR)‐1,3,4,4a,5,7,8,8a‐Octahydro‐2‐methylene‐naphthalene‐6‐one‐1‐propanenitrile,an Important Precursor of Solanapyrones

A novel and facile strategy for stereoselective synthesis of new chiral (1R,4aR,8aR)‐1,3,4,4a,5,7,8,8a‐octahydro‐2‐methylenenaphthalene‐6‐one‐1‐propanenitrile (8) by one‐pot stereoselective hydrogenation/acetalization and Beckmann fragmentation is described. Chiral octalone 8, an important precursor of solanapyrone, was obtained in good yield.