离子液体介质中FeCl3•6H2O催化下芳香醛与5,5-二甲基-1,3-环己二酮的缩合反应

考察了在离子液体1-正丁基-3-甲基咪唑四氟硼酸盐([bmim][BF₄])介质中, 芳香醛与5,5-二甲基-1,3-环己二酮的缩合反应. 实验结果表明, 在催化量的FeCl₃•6H₂O存在下, 该反应可高产率地生成氧杂蒽二酮类化合物3; 而在TMSCl/FeCl₃•6H₂O复合催化体系的催化下, 则得到氧杂蒽二酮类化合物的开环衍生物4, 反应具有非常好的选择性. 该论文提供的方法操作简单、产率高、选择性好而且对环境友好. 在反应结束后, 所用催化剂及离子液体都很容易回收, 并能有效重复使用.     

Palladium‐Catalyzed 2‐Phenylethenylation of Codeine: 8‐[(1E)‐2‐Phenylethenyl]codeinone Dimethyl Ketal as the Unexpected ‘Masked’ Diene for the Preparation of 19‐Substituted Diels–Alder Adducts of Thebaine

In a search for starting materials for the preparation of 7,8‐fused morphine alkaloid derivatives, 8‐[(1E‐2‐phenylethenyl]codeinone dimethyl ketal ( 4 ) and 8‐[(1E‐2‐phenylethenyl]codeine ( 5 ) were prepared. These dienes were used as substrates in the Diels–Alder reactions. Compound 5 formed the ‘normal’ adduct 12 with N‐phenylmaleimide, while compound 4 behaved in reactions with dienophiles as the ‘masked’ diene 11 , a 8‐[(1E)‐2‐phenylethenyl]‐substituted thebaine, yielding the corresponding 19‐substituted 6,14‐endo‐etheno‐6,7,8,14‐tetrahydrothebaines. Specifically, reaction of 4 with methyl vinyl ketone gave rise to 19‐[(1E)‐phenylethenyl]thevinone ( 14 ) whose structure was elucidated by an X‐ray diffraction analysis. The thebaine derivative 11 was also prepared from 4 .     

A density functional study on a biomimetic non-heme iron catalyst: insights into alkane hydroxylation by a formally HO-FeV=O oxidant

The reactivity of [HO-(tpa)Fe(V)=O] (TPA=tris(2-pyridylmethyl)amine), derived from O-O bond heterolysis of its [H(2)O-(tpa)Fe(III)-OOH] precursor, was explored by means of hybrid density functional theory. The mechanism for alkane hydroxylation by the high-valent iron-oxo species invoked as an intermediate in Fe(tpa)/H(2)O(2) catalysis was investigated. Hydroxylation of methane and propane by HO-Fe(V)=O was studied by following the rebound mechanism associated with the heme center of cytochrome P450, and it is demonstrated that this species is capable of stereospecific alkane hydroxylation. The mechanism proposed for alkane hydroxylation by HO-Fe(V)=O accounts for the experimentally observed incorporation of solvent water into the products. An investigation of the possible hydroxylation of acetonitrile (i.e., the solvent used in the experiments) shows that the activation energy for hydrogen-atom abstraction by HO-Fe(V)=O is rather high and, in fact, rather similar to that of methane, despite the similarity of the H-CH(2)CN bond strength to that of the secondary C-H bond in propane. This result indicates that the kinetics of hydrogen-atom abstraction are strongly affected by the cyano group and rationalizes the lack of experimental evidence for solvent hydroxylation in competition with that of substrates such as cyclohexane.     

Use of allyl, 2-tetrahydrofuryl, and 2-tetrahydropyranyl ethers as useful C3-, C4-, and C5-carbon sources: palladium-catalyzed allylation of aldehydes

Palladium-diethylzinc or palladium-triethylborane catalytically promotes self-allylation of 2-(allyloxy)tetrahydrofurans, 2-(allyloxy)tetrahydropyrans, and their hydroxy derivatives on the rings (ribose, glucose, mannose, deoxyribose, deoxyglucose). All the reactions proceed at room temperature and provide polyhydroxyl products, sharing a structural motif of a homoallyl alcohol, in good to excellent yields with high levels of stereoselectivity. Useful C3-unit elongation, which makes the best use of an allyl ether as a protecting group and a nucleophilic allylation agent, is demonstrated. Mechanisms for the umpolung reaction (of an allyl ether into an allylic anion) and stereoselectivity associated with allylation of aldehydes are discussed.     

Aminomethylation of hindered 2-propargyl-1,3-diketones

2-Propargyl-substituted methoxy-1,3-diketones react with alkoxymethylamines or paraform and secondary amines in the presence of CuCl at the acetylene group to afford Mannich bases.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1293–1295, May, 1996.     

A Novel Environmentally Benign Method for the Selective Oxidation of Alcohols to Aldehydes and Ketones

In the presence of [Ru(terpyridine)(2,6‐pyridinedicarboxylate)], aliphatic and benzylic alcohols are oxidized to the corresponding aldehydes or ketones with high selectivity by using hydrogen peroxide as the oxidant. There is no need for the addition of co‐catalysts or organic solvents. By applying an optimized reaction protocol, high catalyst productivity (turnover number>10 000) and activity (turnover frequency up to 14 800 h^?1) has been achieved.     

Stereodivergent total asymmetric synthesis of polyhydroxylated pyrrolidines via tandem allylic epoxidation and intramolecular cyclization reactions

Epoxidation of the allylic alcohols 10 and 11 using the VO(acac)₂/t-BuOOH system followed by an intramolecular 5-exo cyclization of the resulting δ-epoxycarbamates 12, 13, 18, and 19 has been shown to provide a general and efficient solution for the asymmetric synthesis of polyhydroxy pyrrolidines. The requisite vicinal amino alcohol functionality was enantio-/regio-selectively installed by the Os-catalyzed asymmetric aminohydroxylation reaction of the designed achiral olefin 6.     

Synthesis of N-heterocyclic carbene precursors bearing biphenyl units and their use in ruthenium-catalyzed ring-opening metathesis polymerization

A range of new imidazolium and imidazolinium chlorides bearing biphenyl units on their nitrogen atoms was synthesized. They differed by the electron-withdrawing or -donating nature and the steric bulk of the substituents on their aromatic rings. These various N-heterocyclic carbene (NHC) precursors were combined with the [RuCl₂(p-cymene)]₂ dimer and potassium tert-butoxide to generate the corresponding ruthenium-arene complexes [RuCl₂(p-cymene)(NHC)] in situ. The catalytic activity of these species was investigated in the photoinduced ring-opening metathesis polymerization (ROMP) of cyclooctene. The results obtained confirmed the necessity of blocking the ortho-positions of the phenyl rings in the vicinity of the metal center in order to attain high catalytic efficiencies. They also showed that changing the steric and electronic properties of the substituents on the remote phenyl rings of the biphenyl units had no significant influence on the outcome of the polymerization.     

Ruthenium-catalyzed one-pot hydroformylation of alkenes using carbon dioxide as a reactant

A new hydroformylation of alkenes using carbon dioxide as a reactant is shown to take place in the presence of ruthenium cluster complexes and halide salts. Similar or even better yields of alcohols were formed as compared to the conventional hydroformylation with CO under the same reaction conditions. The reaction proceeded in three steps: CO₂ is first converted to CO; then it is used as a reagent for hydroformylation to give aldehyde; subsequently, it is hydrogenated to alcohol. ESI-mass spectrometric analyses of the reaction solutions indicated formation of four kinds of ruthenium anionic complexes including tetra-, tri-, and mononuclear species. On the basis of experimental findings, possible roles of these complexes are discussed.     

Novel metathesis catalysts based on ruthenium 1,3-dimesityl-3,4,5,6-tetrahydropyrimidin-2-ylidenes: synthesis, structure, immobilization, and catalytic activity

The synthesis of novel ruthenium-based metathesis catalysts containing the saturated 1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene ligand, that is, [RuCl2(NHC)[=CH-2-(2-PrO)-5-NO(2)-C6H3]] (1) and [Ru(CF3COO)2(NHC)[=CH-2-(2-PrO)-5-NO2-C6H3]] (2) (NHC=1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene) is described. Both catalysts are highly active in ring-closing metathesis (RCM) and ring-opening cross-metathesis (ROCM). Compound 1 shows moderate activity in enyne metathesis. Compound 2 is not applicable to enyne metathesis since it shows high activity in the cyclopolymerization of diethyl dipropargylmalonate (DEDPM). Poly(DEDPM) prepared by the action of 2 consists of 95% five-membered rings, that is, poly(cyclopent-1-enevinylene)s, and 5 % of six-membered rings, that is, poly(cyclohex-1-ene-3-methylidene)s. The polymerization proceeds in a nonliving manner and results in polyenes with broad polydispersities (1.9< or =PDI< or =2.3). Supported analogues of 2 were prepared by immobilization on hydroxymethyl-Merrifield resin and a monolithic support derived from ring-opening-metathesis polymerization (ROMP). Catalyst loadings of 1 and 2.5%, respectively, were obtained. Both supported versions of 2 showed excellent reactivity. With 0.24-2% of the supported catalysts, yields in RCM and ROCM were in the range of 76-100%. Leaching of ruthenium was low and resulted in Ru contaminations of the products of less than 0.000014% (0.14 ppm).