A new pyridine-2,6-bis(oxazoline) for efficient and flexible lanthanide-based catalysts of enantioselective reactions with 3-alkenoyl-2-oxazolidinones

A new pyridine-2,6-bis(oxazoline) (4) has been easily synthesised from the reaction of (1S,2S)-2-amino-1-phenylpropane-1,3-diol (1) and dimethyl pyridine-2,6-dicarboximidate (2), followed by TIPS (TIPS=triisopropylsilyl) protection of the 4'-CH2OH group. The catalysts derived from 4 and eight lanthanide(III) triflates have been tested over three reactions involving 3-acryloyl- and 3-crotonoyloxazolidinones (5 a,b): the Diels-Alder (DA) reaction with cyclopentadiene, the 1,3-dipolar cycloaddition with diphenyl nitrone and the Mukaiyama-Michael reaction with 2-trimethylsilyloxyfuran. Several reactions exhibit very good enantioselectivity (ee>90 %), and the opposite enantiomers can be easily obtained simply by changing the cation. This specific feature of the ligand can be appreciated in the DA reaction of 5 a, since the catalyst [Sc(III)4] gives the adduct (2'S)-9 a with 99 % ee, whereas the catalyst [Y(III)4] gives the opposite enantiomer with 95 % ee. A rationale of the enantioselectivity is proposed on the basis of the NMR spectra of La-based complexes involving 4 and 5 as ligands.     

Catalytic asymmetric oxidation of cyclic dithioacetals: highly diastereo- and enantioselective synthesis of the S-oxides by a chiral aluminum(salalen) complex

Aluminum(salalen) complex 1 [salalen = half-reduced salen, salen = N,N'-ethylenebis(salicylideneiminato)] was found to be a highly efficient catalyst for asymmetric oxidation of cyclic dithioacetals in the presence of 30% hydrogen peroxide as an oxidant. In the reaction of a series of 2-substituted 1,3-dithianes bearing alkyl, alkenyl, alkynyl, and aryl groups as the substituent, the trans-monoxides were obtained in high yields with 19:1 → >20:1 dr (diastereomeric ratio) and 98-99% ee (enamtiomeric excess). The reaction of nonsubstituted 1,3-dithiane also proceeded in a highly enantioselective manner to give the monoxide with a small formation of the trans-1,3-dioxide, an overoxidation product. Five-membered 1,3-dithiolanes and seven-membered 1,3-dithiepanes also underwent oxidation to give monoxides with high diastereo- and enantioselectivity. It was found that the equilibrium between the two chairlike conformers of dithianes has relevance to the observed diastereoselectivity in the first oxidation process, and the dioxide formation in the oxidation of 1,3-dithiane and its stereochemistry also can be explained by the conformational equilibrium of the product monoxide.     

Practical synthesis of optically active amino alcohols via asymmetric transfer hydrogenation of functionalized aromatic ketones

2-Substituted acetophenones such as 2-cyano-, 2-azido-, or 2-nitroacetophenones were effectively reduced with a mixture of HCOOH/N(C(2)H(5))(3) containing a chiral Ru(II) catalyst, RuCl[(S,S)-N-(p-toluenesulfonyl)-1,2-diphenylethylenediamine](p-cymene), giving the corresponding optically active alcohols, which can be converted to optically active amino alcohols with excellent ee's. Similarly, the reaction of 2-benzoylacetophenone with the same Ru catalyst gave a quantitative yield of the corresponding optically active 1,3-diol with 99% ee.     

Highly exo-selective and enantioselective cycloaddition reactions of nitrones catalyzed by a chiral binaphthyldiimine-Ni(II) complex

[reaction: see text] Significant levels of exo-selectivity (exo:endo = >99:1 to 86:14) and enantioselectivity (95-82% ee) were obtained in the 1,3-dipolar cycloadditions of a number of nitrones with 3-(2-alkenoyl)-2-thiazolidinethiones, using the chiral binaphthyldiimine-Ni(II) complex (5-20 mol %), which was easily prepared form N,N'-bis(3,5-dichrolo-2-hydroxybenzylidene)-1,1'-binaphthyl-2,2'-diamine and Ni(ClO4)2 x 6H2O in CHCl3 in the presence of 4 A molecular sieves, as a chiral Lewis acid catalyst.     

Efficient catalytic effects of Lewis acids in the 1,3-dipolar cycloaddition reactions of carbonyl ylides with imines

[reactions: see text] 1,3-Dipolar cycloaddition reactions between imines and carbonyl ylides generated by tandem intramolecular carbenoid-carbonyl cyclizations were found to be effectively catalyzed by Lewis acids (10 mol %). The Rh2(OAc)4-catalyzed reactions of o-(methoxycarbonyl)-alpha-diazoacetophenone with imines such as N-[2-(benzyloxy)benzylidene]aniline in the absence of Lewis acid gave no 1,3-dipolar cycloaddition products, but rather the dimeric product of the corresponding carbonyl ylide. In contrast, in the presence of Lewis acids such as Yb(OTf)3, the 1,3-dipolar cycloaddition reactions of the corresponding 1-methoxy-2-benzopyrylium-4-olate proceeded smoothly with several imines, giving in most cases exo-selectivity and no formation of the dimeric product. When Yb(OTf)3 was used as a Lewis acid catalyst, a fundamental catalytic effect was also observed in the cycloaddition reactions of imines with carbonyl ylides generated from 1-diazo-5-phenyl-2,5-pentanedione, 1-diazo-2,5-hexanedione and diazomethyl 2,3,4,5-tetrachloro-6-methoxycarbonylphenly ketone. This efficient catalytic effect can be satisfactorily explained in terms of energetics of the cycloaddition in the absence and the presence of Lewis acid by calculations using the ONIOM (B3LYP/6-31G(d):PM3) method.     

Knoevenagel reaction in [MMIm][MSO₄]: synthesis of coumarins

The ionic liquid 1,3-dimethylimidazolium methyl sulfate, [MMIm][MSO?], together with a small amount of water (the amount taken up by the ionic liquid upon exposure to air), acts efficiently as both solvent and catalyst of the Knoevenagel condensation reactions of malononitrile with 4-substituted benzaldehydes, without the need for any other solvent or promoter, affording yields of 92%-99% within 2-7 min at room temperature. When L-proline is used as an additional promoter to obtain coumarins from o-hydroxybenzaldehydes, the reaction also proceeds in high yields. Work-up is very simple and the ionic liquid can be reused several times. Some of the coumarins obtained are described for the first time.     

Unprecedented syndioselectivity and syndiotactic polyolefin melting temperature: polypropylene and poly(4-methyl-1-pentene) from a highly active, sterically expanded eta1-fluorenyl-eta1-amido zirconium complex

The structurally unique, sterically expanded eta1-fluorenyl-eta1-amido single-site precatalyst, Me2Si(eta1-N-tBu)(eta1-C29H36)ZrCl2.OEt2 (3), upon activation with methylaluminoxane (MAO), is remarkably active and constitutes the most syndioselective alpha-olefin polymerization catalyst system yet reported. 3/MAO affords as-prepared syndiotactic polypropylene with [rrrr] > 99% and unprecedented melting temperatures for the unannealed (165 degrees C) and annealed (174 degrees C) polymers. The activity of this system is 4 times that of the prototypical syndioselective catalyst Me2C(eta5-C5H4)(eta5-C13H8)ZrCl2/MAO. The high activity and syndioselectivity of 3/MAO can be extended to the production of syndiotactic poly(4-methyl-1-pentene) with a record melting temperature of 215 degrees C and [rrrr] = 97%.     

Brønsted acids as additives for the direct asymmetric aldol reaction catalyzed by l-prolinethioamides. direct evidence for enamine-iminium catalysis

The use of protonated l-prolinethioamide instead of the free base derivative 1 as the organocatalyst for the direct aldol addition has a profound and appreciable effect on both the yield and the stereochemical course of the reaction. 4-Nitrobenzaldehyde (2) reacts with acetone in the presence of the protonated catalyst 1.TFA, affording aldol product 3 with a yield up to 99% and an ee up to 98%. The catalyst loading can be lowered to 2.5 mol %. More than 20 different acids were investigated as an additive, and its role as cocatalyst has been discussed. Furthermore, reactions of l-prolinethioamide salts with acetone have been monitored using ESI-MS and 1H NMR techniques, giving insight into the mechanism of the direct aldol reaction. The presumed formation of the iminium salt 10 has been unambiguously confirmed.     

N-heterocyclic carbene-catalyzed Michael additions of 1,3-dicarbonyl compounds

A study of the organocatalytic activity of N‐heterocyclic carbenes (NHCs) in the Michael addition of 1,3‐dicarbonyl compounds has allowed us to identify 1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene (IPr) as an excellent catalyst for this transformation (up to 99 % yield with a 2.5 mol % catalyst loading), and the reaction was found to be of broad scope. Two early applications of this unprecedented catalytic activity of NHCs are described, that is, the domino carbocyclization reactions of simple cyclic 1,3‐dicarbonyl and malonic acid derivatives, which allow stereoselective access to bridged bicyclic compounds, and the stereoselective synthesis of cyclohexanols (or cyclohexene). Early mechanistic investigations are also reported.     

Synthesis of 4-Methyl-2-Isopropyl- 1,3 -Dioxolane by TiSiW12O40/ TiO2 as Catalyst

Acetals and ketals are a kind of the important compounds and used to protect carbonyl,middle material of the organic synthesis. What's more, they are a sort of the widely use flavor substance. 4-Methyl-2-isopropyl-1,3-dioxolane has fresh fruit odor and apple note. It is used to producing many sorts of essence. And the conventional method to synthesize 4-methyl-2-isopropyl-1,3-dioxolane makes use of sulfuric acid as catalyst in factories. But it causes many problems, such as the erosion of production equipment, difficulty after-treatment, low quality of the products, etc. HPA and its salts shows excellent catalytic activity to the esterification and have recently attracted much attention as catalysts for various industrial processes, because their acidic and redox properties can be controlled at atomic/molecular levels. Misono, Pope [1], and Wang [2]have reviewed the homogeneous catalysis and fine organic synthesis catalyzed by heteropoly compounds. However, there is no report on the synthesis of 4-methyl-2-isopropyl-1,3-dioxolane catalyzed by TiSiW12O40/TiO2. TiSiW12O40/TiO2 was prepared according to reference [3] and identified by means of IR and XRD. The reaction was carried out in a three-neck flask equipped with a stirrer, a reflux condenser, and a thermometer. A certain amounts of isobutyraldehyde,1,2-propanediol and the catalyst was heated to boiling and refluxed until no water flowed off. The purified product was analyzed by IR spectra and 1HNMR.In this paper, we report 4-methyl-2-isopropyl-1,3-dioxolane was synthesized from isobutyraldehyde and 1,2-propanediol in the presence of TiSiW12O40/TiO2. The factors influencing the yield of product and the optimum reaction conditions were discussed. The optimum conditions are molar ratio of isobutyraldehyde to 1,2-propanediol was 1:1.5, the quantity of catalyst was equal to 0.5% feed stock, and the reaction time was 1.0 h. TiSiW12O40/TiO2 was an excellent catalyst to synthesize 4-methyl-2-isopropyl-1,3-dioxolane and the yield can be up to 92.1%. IR spectra of 4-methyl-2-isopropyl- 1,3-dioxolane shows peaks at 1191,1100,1022,950 cm-1; 1HNMR (δH, ppm):4.65-4.67 (d, 1H, CH), 4.02-4.20 (m, 1H, CH), 3.81-3.92 (d, 1H, CH), 3.35-3.43 (t, 1H, CH),1.61～1.85 (m, 1H, CH), 1.14-1.29 (d, 3H, CH3), 0.96 (m, 6H, CH3); nD20=1.4135; b.p. 127-130 ℃.And we found that the catalyst can be utilized repeatedly, moreover, the catalytic activities of the catalyst are almost unchanged after it has been used five times. From the above results and discussion, we can see that the synthesis of 4-methyl-2-isopropyl-1,3-dioxolane catalyzed by TiSiW12O40/TiO2 instead of sulfuric acid has a great prospect of application.     

Accurate determinations of the extent to which the SE2' reactions of allyl-, allenyl- and propargylsilanes are stereospecifically anti

The allylsilanes, (R)-E- and (R)-Z-4-trimethylsilylpent-2-ene 16, were prepared in essentially an enantiomerically and geometrically pure state (er >99.95 : 0.05, E : Z and Z : E >99.95 : 0.05) by, successively, conjugate addition of lithium dimethylcuprate to N-[(E)-3'-trimethylsilylpropenoyl]-(7S)-10,10-dimethyl-4-aza-5-thiatricyclo[5.2.1.0(3,7)]decane 5,5-dioxide 13, to give N-[(E)-(3'R)-3'-trimethylsilylbutanoyl]-(7S)-10,10-dimethyl-4-aza-5-thiatricyclo[5.2.1.0(3,7)]decane 5,5-dioxide, removal of the chiral auxiliary with bromomagnesium benzyloxide, aldol reaction with acetaldehyde, and decarboxylative elimination, to give either the Z- or E-isomer. Both the E- and Z-allylsilanes 16 reacted with the adamantyl cation to give mixtures of E- and Z-4-adamantylpent-2-enes 17. The E-allylsilane gave the E- and Z-products in a ratio of 40 : 60, and the Z-allylsilane gave the E- and Z-products in a ratio of 99.8:0.02. The enantiomer ratio was >99:1 for the reaction of the E-allylsilane giving the Z-product, 90:10 for the E-allylsilane giving the E-product, and 95 : 5 for the Z-allylsilane giving the E-product, showing that the reactions were stereospecific to a high degree, but not always quite completely so. The allenylsilane, 2-trimethylsilylpenta-2,3-diene 29, was prepared enantiomerically highly enriched (er 99:1) by copper-catalysed reaction of methylmagnesium chloride with (S)-4-trimethylsilylbut-3-yn-2-yl camphor-10-sulfonate 28. The allenylsilane 29 reacted with the adamantyl cation to give (S)-4-adamantylpent-2-yne (S)-30 with the same level of enantiomeric purity, showing that the reaction was, as accurately as can be measured, completely stereospecific. The allenylsilane 29 also reacted with isobutanal in the presence of titanium tetrachloride to give 2,4-dimethylhept-5-yn-3-ol as a mixture of diastereoisomers, syn 31 and anti 32, in a ratio of 95:5, with the major diastereoisomer present as a mixture of enantiomers (4R,5R):(4S,5S) in a ratio of 99:1, showing that the reaction was, as accurately as can be measured, completely stereospecific in the anti sense. The corresponding propargylsilane, 4-trimethylsilylpent-2-yne 37, reacted with the adamantyl cation to give dienes assigned the structures 2,3-diadamantyl-1,3-pentadiene 42 and 2,4-diadamantyl-1,3-pentadiene 43, and reacted with isobutanal in the presence of titanium tetrachloride to give 2-(1-hydroxy-2-methylpropyl)-3-trimethylsilylpenta-1,3-dienes 45 and 2,4-dimethyl-5-trimethylsilylhept-5-en-3-one 46. The enantiomerically enriched propargylsilane (R)-1,3-bis(trimethylsilyl)but-1-yne (er >99.7:0.3) was prepared from the sultam 13, by removal of the chiral auxiliary with lithium ethoxide, reduction of the ethyl ester to give (R)-3-trimethylsilylbutanal 60, enol triflate formation, beta-elimination and C-silylation. The propargylsilane reacted with 2,4-dinitrobenzaldehyde in the presence of titanium tetrachloride to give the allenes, 1-(2,4-dinitrophenyl)-2-trimethylsilylpenta-2,3-dienols 63-66, as two diastereoisomers in a ratio of 2 : 1, each of which was a pair of enantiomers in a ratio of approximately 3:1, showing that there was considerable loss of stereospecificity, but that what there was was in the anti sense. A similar reaction with isobutanal gave a similar set of four allenes, 2-methyl-4-trimethylsilylhepta-4,5-dien-3-ol 73-76, but with a negligible degree of stereospecificity.     

Designing the "search pathway" in the development of a new class of highly efficient stereoselective hydrosilylation catalysts

The direct coupling of oxazolines and N-heterocyclic carbenes leads to chelating C,N ancillary ligands for asymmetric catalysis that combine both an "anchor" unit and a stereodirecting element. Reacting various N-substituted imidazoles with 2-bromo-4(S)-tert-butyl- and 2-bromo-4(S)-isopropyloxazoline gave the imidazolium precursors of the stereodirecting ancillary ligands. A library of ten different ligand precursors was obtained by using this simple procedure (65-97 % yield). These protioligands were metalated in a subsequent step by reaction with [{Rh(mu-OtBu)(nbd)}2] (nbd=norbornadiene), generated in situ from KOtBu and [{RhCl(nbd)}2] giving the corresponding N-heterocyclic carbene complexes [RhBr(nbd)(oxazolinyl-carbene)] 4 a-j in good yields. X-ray diffraction studies of two of the rhodium complexes, 4 d and 4 j, established a distorted square-pyramidal coordination geometry with the bromo ligand occupying the apical position. The rhodium-carbene bond length was found to be 2.070(4) A (4 d) and 2.012(3) A (4 j). Complexes 4 a-j were treated with AgBF4 in dichloromethane, giving the active cationic square-planar catalysts for the hydrosilylation of ketones. As a reference reaction for the catalyst optimisation, the hydrosilylation of acetophenone with diphenylsilane was studied and the system optimised with respect to the counterion (BF(4) (-)), solvent (THF) and the silane reducing agent (diphenylsilane). The reaction product (1-phenylethanol) was obtained with the highest enantiomeric excess (ee) by carrying out the reaction at -60 degrees C, whilst the enantioselectivity drops upon going both to lower and higher temperatures. The observation that the temperature dependence of the ee values goes through a maximum indicated a change in the rate-determining step as the temperature is varied. The determination of the initial reaction rate in the hydrosilylation of acetophenone upon varying the catalyst (4 d) and substrate concentrations at -55 degrees C established a rate law for the initial conversion which is first-order in both substrates as well as the catalyst (Vi = k[4][PhCOMe][Ph2SiH2]). The catalytic system derived from complex 4 d was found to afford high yields and good enantioselectivities in the reduction of various aryl alkyl ketones (acetophenone: 92 % isolated yield and 90 % ee, 2-naphtyl methyl ketone: 99 % yield, 91 % ee). The selectivity for the reduction of prochiral dialkyl ketones is comparable or even superior to the best previously reported for prochiral nonaromatic ketones; whereas cyclopropyl methyl ketone is hydrosilylated with an enantioselectivity of 81 % ee, the increase of the steric demand of one of the alkyl groups leads to improved ee's, reaching 95 % ee in the case of tert-butyl methyl ketone. Linear chain n-alkyl methyl ketones, which are particularly challenging substrates, are reduced in good asymmetric induction, such as 2-octanone (79 % ee) and even 2-butanone (65 % ee).     

A silica-supported, switchable, and recyclable hydroformylation-hydrogenation catalyst

A homogeneous hydroformylation catalyst, designed to produce selectively linear aldehydes, was covalently tethered to a polysilicate support. The immobilized transition-metal complex [Rh(A)CO]+(1+)), in which A is N-(3-trimethoxysilane-n-propyl)-4,5-bis(diphenylphosphino)phenoxazine, was prepared both via the sol-gel process and by covalent anchoring to silica. 1+ was characterized by means of (31)P and (29)Si MAS NMR, FT-IR, and X-ray photoelectron spectroscopy. Polysilicate immobilized Rh(A) performed as a selective hydroformylation catalyst showing an overall selectivity for the linear aldehyde of 94.6% (linear to branched aldehyde ratio of 65). In addition 1-nonanol, obtained via the hydrogenation of the corresponding aldehyde, was formed as an unexpected secondary product (3.6% at 20% conversion). Under standard hydroformylation conditions, 1+ and HRh(A)(CO)(2)(1) coexist on the support. This dual catalyst system performed as a hydroformylation/hydrogenation sequence catalyst (Z), giving selectively 1-nonanol from 1-octene; ultimately, 98% of 1-octene was converted to mainly 1-nonanal and 97% of the nonanal was hydrogenated to 1-nonanol. The addition of 1-propanol completely changes Z in a hydroformylation catalyst (X), which produces 1-nonanal with an overall selectivity of 93%, and completely suppresses the reduction reaction. If the atmosphere is changed from CO/H(2) to H(2) the catalyst system is switched to the hydrogenation mode (Y), which shows a clean and complete hydrogenation of 1-octene and 1-nonanal within 24 h. The immobilized catalyst can be recycled and the system can be switched reversibly between the three "catalyst modes" X, Y, and Z, completely retaining the catalyst performance in each mode.     

Construction of mononitrogen heterocycles with a combined system of 1-azaspiro[4.n]alkene and 3-benzazocine fragments through the intramolecular eight-membered Heck cyclization

Amides, obtained from 1-azaspiro[4.n]alkenes (n = 3, 4, 5) and 2-(6-bromo-1,3-benzo-dioxol-5-yl)acetyl chloride, upon heating with a Herrmann—Beller palladium catalyst undergo intramolecular cyclization by the Heck reaction to form pentacyclic compounds (up to 94% yield) including an 1-azaspiro[4.n]alkene (n = 4, 5) fragment and a new eight-membered 3-benzazocine ring. The structure of the thus obtained pentacycles with the 1-azaspiro[4.4]non-7-ene fragment is isomeric to the structure of the main core of alkaloid cephalotaxine. In the case of 1-azaspiro[4.5]dec-2-ene derivative, the reaction is accompanied by the reduction of bromo amide, with the yield of the cyclization product being 34%. The starting 1-azaspiro-[4.n]alkenes (n = 3, 4, 5) were synthesized by the reductive diallylboration of 3-chloropropion-itrile or the corresponding lactams (piperidin-2-one, (2S)-2-hydroxymethyl-and 5,5-di-methylpyrrolidin-2-one) with subsequent intramolecular metathesis upon the action of Grubbs catalyst.     

Diruthenium(II,III) bis(tetramethyl-1,3-benzenedipropionate) as a novel catalyst for tert-butyl hydroperoxide oxygenation

The reaction of Ru2(OAc)4Cl with 2.2 equiv of H2esp (esp = alpha,alpha,alpha',alpha'-tetramethyl-1,3-benzenedipropionate) resulted in a new compound, Ru2(esp)2Cl (1), that is soluble in organic media. 1 is an active catalyst for the oxygenation of organic sulfides by tert-butyl hydroperoxide (TBHP) in both an acetonitrile solution or neat (solvent-free) conditions. Solvent-free reactions display the quantitative utility of TBHP and hence excellent chemical selectivity for sulfoxide formation.     

Development of a Continuous‐Flow System for Asymmetric Hydrogenation Using Self‐Supported Chiral Catalysts

Well‐designed, self‐assembled, metal–organic frameworks were constructed by simple mixing of multitopic MonoPhos‐based ligands ( 3 ; MonoPhos=chiral, monodentate phosphoramidites based on the 1,1′‐bi‐2‐naphthol platform) and [Rh(cod)₂]BF₄ (cod=cycloocta‐1,5‐diene). This self‐supporting strategy allowed for simple and efficient catalyst immobilization without the use of extra added support, giving well‐characterized, insoluble (in toluene) polymeric materials ( 4 ). The resulting self‐supported catalysts ( 4 ) showed outstanding catalytic performance for the asymmetric hydrogenation of a number of α‐dehydroamino acids ( 5 ) and 2‐aryl enamides ( 7 ) with enantiomeric excess (ee) ranges of 94–98 % and 90–98 %, respectively. The linker moiety in 4 influenced the reactivity significantly, albeit with slight impact on the enantioselectivity. Acquisition of reaction profiles under steady‐state conditions showed 4 h and 4 i to have the highest reactivity (turnover frequency (TOF)=95 and 97 h^?1 at 2 atm, respectively), whereas appropriate substrate/catalyst matching was needed for optimum chiral induction. The former was recycled 10 times without loss in ee (95–96 %), although a drop in TOF of approximately 20 % per cycle was observed. The estimation of effective catalytic sites in self‐supported catalyst 4 e was also carried out by isolation and hydrogenation of catalyst–substrate complex, showing about 37 % of the Rh^I centers in the self‐supported catalyst 4 e are accessible to substrate 5 c in the catalysis. A continuous flow reaction system using an activated C/ 4 h mixture as stationary‐phase catalyst for the asymmetric hydrogenation of 5 b was developed and run continuously for a total of 144 h with >99 % conversion and 96–97 % enantioselectivity. The total Rh leaching in the product solution is 1.7 % of that in original catalyst 4 h .     

Chiral bis(2-oxazolinyl)xanthene (xabox)/transition-metal complexes catalyzed 1,3-dipolar cycloaddition reactions and Diels-Alder reactions

A series of chiral 4,5-bis(2-oxazolinyl)-(2,7-di-tert-butyl-9,9-dimethyl)-9H-xanthenes (xabox) and their transition-metal complexes were synthesized. The X-ray analysis of xabox-RhCl₃ complex shows a unique facial type structure. Xabox-Bn-Mn(II) and xabox-Bn-Mg(II) complexes were found to be efficient catalysts in nitrone 1,3-dipolar cycloaddition (1,3-D.C.) reaction resulting in good to excellent enantioselectivities ranging from 96:4 to >99:1of endo/exo ratio and 91-96% ee for the endo adduct. The correlation between enantiomeric excess of the ligand and the product in the nitrone 1,3-D.C. reaction shows a clear linear relationship, which suggests xabox-metal catalyst worked as a single molecular catalyst. In addition, xabox-i-Pr-Mn(II) complex was also found to be an active catalyst for Diels-Alder (D-A) reaction of acryloyloxazolidinone and cyclopentadiene affording the corresponding cycloadduct in quantitative yield along with 82% ee and 98:2 endo/exo ratio.     

Catalytic performance of [Bmim][Co(CO)4] functional ionic liquids for preparation of 1,3-propanediol by coupling of hydroesterification-hydrogenation from ethylene oxide

In this paper, synthesis of 1,3-propanediol (1,3-PDO) through coupling of hydroesterification-hydrogenation from ethylene oxide (EO) catalyzed by 1-butyl-3-methylimidazolium cobalt tetracarbonyl [Bmim][Co(CO)₄] functional ionic liquid which was prepared by metathesis reaction between [Bmim]Cl and KCo(CO)₄ has been studied. The structure of [Bmim][Co(CO)₄] was characterized by FT-IR and ¹H NMR. Using [Bmim][Co(CO)₄] as catalyst and [Bmim]PF₆ as solvent, 1,3-PDO was prepared for the first time by coupling of hydroesterifaction of EO and hydrogenation of methyl 3-hydroxypropionate (3-HPM). The yield of 3-HPM can reach 90.8%, while the yield of 1,3-PDO up to 82.9%. The catalyst can be separated from the product mixture by extraction with deionized water and recycled several times without significant loss of catalytic efficiency. A possible reaction mechanism has also been proposed.     

Substituted 2-methylene-1,3-oxazolidines, -1,3-thiazolidines, -1,3-benzothiazines, -1,3-oxazines, and substituted imidazopyrimidinediones from Cl(CH2)nNCO and Cl(CH2)nNCS and active methylene compounds

The reaction of omega-chloroalkyl isocyanates Cl(CH2)nNCO (n = 2 (2), 3 (4)) and isothiocyanate Cl(CH2)2NCS (3) with active methylene compounds CH2YY' 1 in the presence of Et3N or Na give 2-YY'-methylene-1,3-oxazolidines, (E,Z)-1,3-thiazolidines, and 1,3-oxazines from 2, 3, and 4, respectively. 2-(Chloromethyl)phenyl isocyanate 8 gives with 1 the corresponding benzo-oxazines. Ethyl 2-isothiocyanatobenzoate 10 gives the corresponding benzothiazolinone, whereas the analogous isocyanate 12 gives noncyclic enols. Ethoxycarbonyl isothiocyanate 14 gives an open-chain thioenol or an enol-thioamide. The cyanoamides CH2(CN)CONHR, R = H, Me, CHPh2, give with Et3N and 2 the bicyclic imidazopyrimidinediones 16, derived from two molecules of 2, but with their preformed Na salt they give the 1,3-oxazolidines. Reaction of cyanoacetamide with 3 in the presence of Na gave a tricyclic triaza(thia)indacene, derived from two molecules of 3. A reaction mechanism involving an initial attack of the anion 1- on the N=C=X (X = O, S) moiety gives an anion 18, which cyclizes intramolecularly and after tautomerization gives the mono-ring heterocycle. With the cyanoamides, the N- site of the ambident ion 18 attacks another molecule of 2 giving the anion 20, which by intramolecular attack on the CN, followed by expulsion of the Cl- gives the bicyclic 16 after tautomerization.     

室温离子液体中乙酸钠和氯苄催化合成乙酸苄酯

在多种1,3-二烷基咪唑和烷基吡啶室温离子液体中考察了较温和条件下乙酸 钠和氯化苄作用合成乙酸苄酯反应。在反应温度下（60 ℃）,熔融的三水合乙酸 钠与离子液体相混溶,氯苄同乙酸钠作用得到乙苄酯,它与四氟硼酸1-乙基-3-甲 基咪唑离子液体不溶而分层。反应结束后产物乙酸苄酯可直接倾析得到,乙酸苄酯 产率达到90%,纯度超过99%。此离子液体催化体系简化了产物分离,离子液体可以 重复使用。