Biomimetic Alkene Epoxidation and Alkane Hydroxylation with Sodium Periodate Catalyzed by Mn(III)-salen Supported on Amberlite IRA-200

Summary. The Mn(III)-salen, containing phosphonium groups at the 5,5′-positions of the salen ligand supported on Amberlite IRA-200 via electrostatic binding was used for the oxidation of alkenes and alkanes with sodium periodate at room temperature in the presence of imidazoles as axial ligands, and the effect of solvent, different axial ligands, and various oxygen donors was investigated. This heterogenized catalyst shows high catalytic activity in alkene epoxidation and alkane hydroxylation. It showed high selectivity in the epoxidation of stilbenes, α-pinene, and (R)-(+)-limonene, and exhibits a particular ability to epoxidize linear alkenes. The stability and reusability of this new heterogenized metallo-salen complex was also investigated. The catalyst was characterized by FTIR, UV-Vis, SEM, and thermal analysis.     

New Method for the Synthesis of 5‐Hydroxycamptothecin Derivatives

Abstract

An efficient hydroxylation at the 5‐position of the C ring of camptothecins was accomplished with the complex of CuI and organic amines as catalyst in the presence of oxygen at room temperature in dimethyl formate (DMF). To be successfully hydroxylated, the insoluble camptothecin analogue was transformed to the corresponding 20 carbonates.     

Study on the bioactivity changes of hydroxylated sulfonylureas derivatives: A possible metabolism

Some new sulfonylureas and their hydroxylation products had been synthesized from 2-amino-4-methylpyrimidine. Their bioactivities against E. coli AHAS II in vitro were tested and the results indicated that the hydroxylation decreased the inhibition activities of sulfonylureas significantly. Subsequently herbicidal tests against stem-growth of barnyard grass and root-growth of rape confirmed the above conclusion. The preliminary molecular docking studies were also carried out to investigate the binding modes of non-hydroxylated and hydroxylated sulfonylureas with AHAS.     

Copper-mediated regio- and stereoselective 12β-hydroxylation of steroids with molecular oxygen and an unexpected 12β-chlorination

It is shown, that copper(I) complexes of 17-(2-iminomethyl)pyridino steroids (17-IMPY steroids) can react with molecular oxygen followed by a regio- and stereoselective γ-hydroxylation in 12β-position. After decomplexation and hydrolysis of the IMPY group 12β-hydroxy-17-ketones are available in practical useful yields. IMPY compounds are simple to prepare by condensation of oxo compounds with (2-aminomethyl)pyridine. In the cases of 17-IMPY steroids the yields in the hydroxylation procedure of an unactivated CH₂ group are higher by starting with copper(II) complexes, reduction with benzoin/triethylamine in acetone and reaction with molecular oxygen in comparison to the direct reaction of copper(I) complexes with molecular oxygen in acetone. Employing the procedure in dichloromethane as solvent starting with copper(II) complexes surprisingly the 12β-chloro compound could be isolated next to the hydroxylation product. This regio- and stereoselective γ-chlorination takes place also in acetone, when triethylammonium chloride is added to the reaction mixture. Oxygen is necessary for this reaction. The mechanistic and stereochemical aspects of these new reactions are discussed. Comparison of the different yields of steroids with different A-ring [3-methoxy-estra-1,3,5(10)-triene and 3β-hydroxy-androst-5-ene] pointed out to a subtle influence of the molecular structure far from the reaction centre on these reactions. The successful hydroxylation of the IMPY derivative of 3β-hydroxy-androst-5-ene-17-one shows the tolerance of a homoallylic system against this oxidation procedure. By Oppenauer oxidation 12β-hydroxy-androst-4-ene-3,17-dione is available. The hydroxylation procedure opens a short way to 12β-hydroxy-17-oxo steroids, which are difficult to obtain by other routes.     

The catalysis of some novel polystyrene-supported porphyrinatomanganese(III) in hydroxylation of cyclohexane with molecular oxygen

Some novel polystyrene-supported porphyrinatomanganese(III) in which alkyl group is bonded to the surface of polystyrene, PS-[Mn(HPTPP)Cl](C_nH_2n+1) (n=2, 6, 8, 18), have been synthesized. Their catalytic activities to hydroxylate cyclohexane in PS-[Mn(HPTPP)Cl](C_nH_2n+1)–O₂–ascrobate system have been found to be higher compared with corresponding non-supported porphyrinatomanganese(III) and increase with the increase of the length of alkyl. These results are discussed in the point of view of metalloporphyrin microenvironment.     

镱钼钒磷四元杂多化合物催化苯酚羟化反应的研究

合成了具有Keggin结构镱钼钒磷杂多化合物 ,用IR、UV、XRD、ICP等手段对其结构进行了表征。并研究了该杂多化合物对苯酚过氧化氢羟化反应的催化活性。实验结果表明 :以甲醇为溶剂 ,用镱钼钒磷杂多化合物为催化剂 ,当n(phOH)∶n(H2 O2 ) =1∶2 ,反应体系的pH =5.0 ,反应时间 4h ,苯酚转化率为 4 1 66% ,对苯二酚产率可达到 4 0 .2 4 %。     

负载型铜系分子筛催化剂在苯酚羟基化反应中的应用

以介孔分子筛MCM-41、MCM-48和AIMCM-41以及微孔分子筛Naβ和MOR为载体,分别采用有机官能团化法和分步水热合成法制备了系列负载型催化剂,考察了其在苯酚羟基化反应中的活性;得到了不同载体类型、不同负载方法及不同助剂与反应活性的对应关系．结果表明：以微孔分子筛为载体的催化剂对副产物有明显的抑制作用．介孔分子筛AIMCM-41,MCM-41,MCM--48为载体时,催化剂在苯酚羟基化反应中的活性顺序为AIMCM-41〉MCM-48〉MCM-41,助剂镧和钴的引入可以有效抑制副产物的产生．     

活性炭载铁催化剂作用下几种典型芳烃一步氧化羟基化反应研究

以过氧化氢为氧化剂, 在乙腈介质中研究了几种典型芳烃的一步羟基化反应, 考察了底物取代基的供吸电子性质、 空间位阻等对羟基化反应的影响, 并推测了其反应机理.     

Oxidation of alkanes by Ph4PHSO5 catalyzed by manganese(III) porphyrins. A study of the factors determining alcohol and ketone formation

As reported in previous papers, the oxidation of ethylbenzene with Ph₄PHSO₅ catalyzed by Mn(TMP)Cl in the presence of nitrogen bases in 1,2-dichloroethane homogeneous solution affords fair yields (up to 80%) of oxygenated products. Acetophenone is the major product together with minor amounts of 1-phenylethanol ([ketone]/[alcohol]6). In this paper we report further observations concerning this system. In particular we find that a similar products distribution is observed when soluble Co(II) or Fe(II) species, i.e. acetylacetonate derivatives, are used instead of the manganese porphyrin. On the other hand for these compounds, which are catalysts of radical reactions, the product distribution is determined by a remarkably larger reactivity of the alcohol initially formed compared with that of the alkane (k_R–OH/k_R–H200). The product distribution for the Mn(TMP)Cl catalysis cannot be rationalized on the same basis. Direct experiments show that the reactivity of the two substrates is similar (k_R–OH/k_R–H2–6) thus suggesting that a mechanism different from the simple radical hydrogen atom abstraction is taking place. The dependence of the chemioselectivity of hydrocarbon oxidation on the nature of the manganese porphyrin employed and of a number of additives indicates that the product distribution is mainly determined by the relevance of the association of the alcohol intermediate to the catalyst prior to the second oxidation step leading to ketone. Two different rho Hammett's values are obtained for ethylbenzenes oxidation depending on the method employed for the measurement of reaction rates, i.e. by separate or by competitive experiments thus providing further mechanistic information on the association of the substrates to the oxo-species.     

Initial stages of H2O adsorption and hydroxylation of Fe-terminated α-Fe2O3(0 0 0 1) surface

The adsorption modes of H₂O on a Fe-terminated hematite(0 0 0 1) surface have been investigated by first principles Density Functional theory within a periodic slab model and the generalized gradient approximation. Molecular adsorption and dissociative adsorption in monolayer coverage, one H₂O per surface Fe, were both considered. Five plausible orientations were studied to determine the most favorable adsorption position. Molecular adsorption is shown to have a small effect on the underlying surface structure, while hydroxylation has a strong effect on the surface geometry. Electronic densities of state calculations reveal details of these different interactions. The heterolytic dissociation, which produces two types of surface hydroxyls, is the preferable adsorption mode, being slightly favored energetically over the molecular adsorption. Homolytic dissociative adsorption, forming a single hydroxyl on surface Fe, is energetically unfavored, even though strong binding interaction (∼3 eV) is found between the OH radical and surface. Dissociative adsorption on an oxidized ferryl site was also studied to investigate suggested local reactivity enhancement.