Epoxide as precatalyst for metal-free catalytic transesterification

Transesterification of methyl esters was accelerated by an in situ-generated metal-free catalyst comprising a quaternary alkylammonium salt and an epoxide. The combination of a quaternary alkylammonium acetate and glycidol is optimal, and various esters were synthesized from methyl esters with alcohols in good to excellent yield. Analysis of the catalyst solution revealed that basic species are generated by the ring-opening reaction of epoxide.     

Highly active double metal cyanide complexes： Effect of central metal and ligand on reaction of epoxide/CO2

Various novel double metal cyanide (DMC) catalysts were successfully prepared by modifying the central metal (M) and one of cyanide ion (CN-) in Zna[M(CN)b]c complex. Such modifications have significant impact on the catalytic efficiency as well as the polymer selectivity for the reaction of PO/CO2. Zn–Ni(Ⅱ) DMC is a potential catalyst for alternating copolymerization of PO/CO2, and DMC catalysts based on Zn3[Co(CN)5X]2 (X = Br-and N3-) exhibit moderate efficiency for the production of polycarbonates. This research presents the preliminary exploration of novel DMC complex via chemical modification of its central metal and ligand.     

UMCM-1-NH_2的后合成修饰及在制备β-氨基醇反应中的应用

采用后合成修饰(PSM)技术将水杨醛锚装到UMCM-1-NH_2上,得到席夫碱功能化的多孔金属-有机骨架化合物UMCM-1-NH-Sal,在该化合物孔道内的席夫碱N、O原子上螯合铜离子得到UMCM-1-NH-Sal-Cu催化剂,并用核磁共振氢谱(1H NMR)、X射线衍射(PXRD)、热重分析(TG)、N_2吸附-脱附等手段对催化剂进行了表征,将其用于催化有机胺和环氧化物的开环反应制备β-氨基醇,结果表明该催化剂具有良好的催化效果.     

环氧水解酶在不对称合成中的应用

环氧水解酶是一种普遍存在于生物体内的酶,它能选择性水解环氧生成相应的手性二醇。这种酶在催化反应中通常显示出十分高的对映立体选择性,生成高光学活性的环氧和二醇。近年来国际上采用微生物来源的环氧水解酶对环氧底物进行不对称水解,然后再通过酸处理未开环的环氧化物“一锅法”高产率、高选择性的生成单一构型的手性二醇。这一新发展为这种酶在精细合成工业上的运用开辟了广阔的前景。     

Chemo-enzymatic enantio-convergent asymmetric synthesis of (R)-(+)-Marmin

Asymmetric biohydrolysis of trisubstituted terpenoid oxiranes (rac-1a-rac-3a) was accomplished by employing the epoxide hydrolase activity Rhodococcus and Streptomyces spp. Depending on the biocatalyst, the biohydrolysis proceeded in an enantio-convergent fashion and gave the corresponding vic-diols in up to 97% ee at conversions beyond the 50%-threshold. In order to avoid a depletion of the ee of product by further oxidative metabolism, bioconversions had to be conducted in an inert atmosphere with exclusion of molecular oxygen. The synthetic applicability of this method was demonstrated by the asymmetric total synthesis of the monoterpenoid coumarin (R)-(+)-Marmin in 95% ee.     

Autoxidation of isotachysterol

Isotachysterol, the acid-catalyzed isomerization product of vitamin D₃, produces seven previously unknown oxygenation products in a self-initiated autoxidation reaction under atmospheric oxygen in the dark at ambient temperature. They are (5R)-5,10-epoxy-9,10-secocholesta-6,8(14)-dien-3β-ol (6a), (5S)-5,10-epoxy-9,10-secocholesta-6,8(14)-dien-3β-ol (6b), (10R)-9,10-secocholesta-5,7,14-trien-3β,10-diol (7a), (10S)-9,10-secocholesta-5,7,14-trien-3β,10-diol (7b), (7R,10R)-7,10-epoxy-9,10-secocholesta-5,8(14)-dien-3β-ol (8), 5,10-epidioxyisotachysterol (9) and 3,10-epoxy-5-oxo-5,10-seco-9,10-secocholesta-6,8(14)-dien-10-ol (10). The formation of these products is explained in terms of free radical peroxidation chemistry.     

Revisiting the Corey-Chaykovsky reaction: the solvent effect and the formation of β-hydroxy methylthioethers

The classical Corey-Chaykovsky (CC) reaction of ketones in ethereal solvents (i.e., THF or Et₂O) resulted in the production of a significant amount of β-hydroxy methylthioether 2 along with normal epoxide product 1. Some interesting and synthetically useful transformations of the CC reaction product of cyclopropyl ketones were also described.     

Improved Ritter reaction with CF3-containing oxirane for an access to central units of protease inhibitors

The influence of fluorinated alcohols on the BF₃·Et₂O-promoted Ritter type reaction has been investigated. Trifluoroethanol/BF₃·Et₂O system allowed access to the central unit of protease inhibitors by the ring opening of fluorinated epoxide 2 with various nitriles.