利用甘露醇骨架和Pauson-Khand反应合成光学纯的C2轴对称性多环酮类结构

以D-甘露醇转化得到的骨架为支架经Pauson-Khand反应成功实现了高度区域和立体选择性地合成具有C2对称性的多官能团的多环手性化合物1,并采用核磁共振和X单晶衍射等分析方法对化合物1的结构进行了讨论.     

C2型轴对称手性双噁唑啉的合成及其应用研究

本文综述了手性双恶唑啉的合成及其金属配合物作为手性催化剂在催化不对称反应中的应用研究进展。     

Efficient C2-Symmetric Chiral Schiff Bases for Lanthanide-catalyzed Asymmetric Hydrogenation of Acetophenone

The finding of new chiral metal catalysts for enantioselective reactions has been the subject of many investigations in recent years1,2. Metal-catalyzed, especially transition metal-catalyzed asymmetric hydrogenation of prochiral ketones was an efficient …     

Desymmetrization of C2-Symmetric Bis(Boronic Esters) by Zweifel Olefinations

anti-Configured 1,3-dimethyl deoxypropionate motifs are important sub structures in natural products. Herein, we describe a bidirectional approach for the rapid construction of natural products featuring such motifs by using C₂-symmetrical 1,3-bis(boronic esters). As for its application in convergent syntheses it was important to establish a selective mono-Zweifel olefination we describe the scope and limitations by using different 1,3-bis(boronic esters) and nucleophiles. This protocol takes advantage of the combination of the Hoppe–Matteson–Zweifel chemistry, which was elegantly put into practice by Aggarwal et al. In order to show its applicability the total syntheses of two natural products, serricornin and (+)-invictolide, were performed.     

An Approach to the Core Structure of CP-225,917

The complex natural product CP-225, 917 (1), which is an inhibitor of Ras fanesyl tranferase,[1～3] has at tracted much attention of several groups for its total synthesis. Our own approach is based on siloxy Cope rearrangement, which could be accomplished thermally in very good yield (99%) to from 10 to 11,[4] a model compound lacking the side arms of the natural product. Its synthetic route from 6 is shown.     

An Efficient Approach to 2-CF3-Indoles Based on ortho-Nitrobenzaldehydes

The catalytic olefination reaction of 2-nitrobenzaldehydes with CF₃CCl₃ afforded stereoselectively trifluoromethylated ortho-nitrostyrenes in up to 88% yield. The reaction of these alkenes with pyrrolidine permits preparation of α-CF₃-β-(2-nitroaryl) enamines. Subsequent one pot reduction of nitro-group by Fe-AcOH-H₂O system initiated intramolecular cyclization to afford 2-CF₃-indoles. Target products can be prepared in up to 85% yields. Broad synthetic scope of the reaction was shown as well as some followed up transformations of 2- CF₃-indole.     

An Efficient Approach to Patchouli Alcohol Analogues

A short approach to the tricyclo [5.3.1.0^3,8] undecane derivatives 1, 10, 11 and 12 and to the tricyclo [4.3.1.0^3,7] decane derivative 2 , starting from industrially available intermediates, is described. Of the compounds 1 , 10 , 11 , and 12 , which possess the ring system of patchouli alcohol, 12 also exhibits a woody, patchouli-like note. The ¹H-NMR.-spectra of 1 , 2 and 8 – 12 are discussed.     

An Efficient Approach to the 2-Nonulosonic Acid Skeleton Through a Hetero-Diels-Alder Reaction

Abstract

The hetero-Diels-Alder reaction of 1,3-diene-polyols with glyoxylates is an expeditious way to build up the skeleton of ulosonic acids. This paper reports an efficient means to improve the yields and the stereoselectivity associated with the hetero-cycloaddition of the activated 1,3-diene, 2S,3S-4E-1-O-Benzyl-2,3-O-isopropylidene-6-ter-butyldimethylsilyloxyhepta-4,6-diene-1,2,3-triol (3) with the dienophile ethyl glyoxylate. The effects of temperature, catalyst, and solvent on the outcome of the Diels-Alder reaction were investigated. The cycloaddition can proceed smoothly even at ?78°C and the complex bis [3-(heptafluorobutyryl)camphorato]oxovanadium (8) was found to be a very efficient catalyst for the cycloaddition reaction. The satisfactory selectivity (endo/exo: 97:3 and re/si: 82:18) observed in this catalytic reaction shows that there is a match effect between the substrate and catalyst.     

由4-甲氧基-2-溴代丁烯内酯合成螺环-环丙烷类化合物的研究

以4-甲氧基-2-溴代丁烯内酯为合成子,在温和条件下与不同的亲核试剂通过串联的双Michael加成及分子内的亲核取代反应,得到螺环-环丙烷类化合物8a～8d.通过元素分析,IR,¹HNMR,¹³CNMR和MS对化合物进行了结构表征,其中化合物8d经单晶X射线衍射测定,确定了其立体化学结构.     

An Efficient Approach to 6, 7-Disubstituted-1H-quinoxalin-2-ones

A novel approach to the synthesis of 6, 7-disubstituted-1H-quinoxalin-2-ones is described.The title compounds were regioselectively prepared by starting from substituted phenylamines andchloroacetyl chloride through the efficient sequence of acylation, nitration, reduction, intramolecularalkylation, and oxidation. 6, 7 -Disubstituted-1H-quinoxalin-2-ones, regioselective, substituted phenylamine.     

Synthesis of Novel Chiral C2-Symmetric Bisoxazoline Ligands Containing 2,5-Di( m -substituted)phenyl-1,3,4-oxadiazole

Abstract

Seven novel chiral C₂-symmetric substituted bisoxazoline ligands containing 2,5-di(m-substituted)phenyl-1,3,4-oxadiazole have been synthesized from 2,5-di-(m-carboxylphenyl)-1,3,4-oxadiazole and aminoalcohol by NaOH or Et₃N cyclization method via halogenated amide intermediate.     

C2-Symmetric enantiopure ethanotethered bis(alpha,beta-butenolides) as templates for asymmetric synthesis. Application to the synthesis of (+)-grandisol

Starting from D-mannitol, we have prepared several C(2)-symmetric ethanotethered bis(alpha,beta-butenolides) and studied their [2+2] photocycloaddition reaction with ethylene. The protective groups of the central diol unit have a noticeable influence on the facial selectivity of the cycloaddition, the bis(trimethylsilyloxy) derivatives showing the highest diastereoselectivity. A theoretical conformational analysis of the substrates in the ground state is in good agreement with the diastereofacial selectivity experimentally observed. The bis(photocycloadducts) have been converted into the enantiopure cyclobutanes formally derived from the photoreaction of ethylene with gamma-hydroxymethyl-alpha,beta-butenolide, in which only a moderate facial selectivity had been previously found. As an application of these studies, we have developed a highly efficient and stereoselective synthesis of (+)-grandisol.     

Bidirectional asymmetric allylboration. A convenient asymmetric synthesis of C(2)-symmetric 3-methylenepentane-1,5-diols and rapid access to C(2)-symmetric spiroketals

The double allylboration of aldehydes using 1, 3-bis(diisopinocampheylboryl)-2-methylenepropanes (R,R)-3 and (S, S)-3 under Brown's salt-free conditions provides C(2)-symmetric 3-methylenepentane-1,5-diols 1 in excellent enantiomeric excess. The absolute stereochemistry of the products was confirmed by a single-crystal X-ray study of bis-Mosher ester 6g. Desymmetrization and further functionalization of diol 1a were achieved by treatment of the bis-BOC carbonate 13 with IBr in toluene at -80 degrees C to give cyclic iodocarbonate 14 as a single diastereomer. This methodology is also applicable in natural product synthesis; enantiomerically pure spiroketals 1,7-dioxaspiro[5.5]undecanes 18 and 25, the latter representing an expedient synthesis of the AB ring system of the spongistatins 20, were easily accessed from simple starting materials in excellent yields and selectivities.     

Efficient synthesis of the C(1)-C(9) fragment of amphidinolides C, C2, and F

The synthesis of the C(1)-C(9) fragment of amphidinolides C, C2, and F was achieved by using a vinyloguous Mukaiyama aldol reaction on a chiral aldehyde with a silyloxyfuran and by using a C-glycosylation of a lactol derivative with an acetyl oxazolidinethione. From the available chiral acetonide-glyceraldehyde, all the stereogenic centers were perfectly induced along the synthesis. The C(1)-C(9) fragment was synthesized as a vinyl stannane at C(9) in 10 steps, with 16% yield.     

C(2)-Symmetric bis-sulfoxide: A novel chiral auxiliary for asymmetric desymmetrization of cyclic meso-1,2-diols

A new heterocyclic compound, C(2)-symmetric bis-sulfoxide 1, has been found to be an efficient chiral auxiliary for asymmetric desymmetrization of cyclic meso-1,2-diols via diastereoselective acetal fission. Both (R,R)- and (S,S)-1 are readily synthesized with high optical purity via asymmetric oxidation of 1, 5-benzodithiepan-3-one (2). After acetalization of meso-1,2-diols 6a-e and a mono-TMS ether 6f with this chiral auxiliary 1, the resulting acetals 7a-f were subjected to base-promoted acetal fission upon treatment with potassium hexamethyldisilazide (KHMDS) followed by acetylation or benzylation to give the desymmetrized diol derivatives 8a-f with high diastereoselectivity. The chiral auxiliary 1 is readily removed by acid-promoted hydrolysis and can be recovered without a loss in enantiomeric excess.     

C2-Symmetric diphenylphosphoramide and diphenylthiophosphoramide derived from (1R,2R)-1,2-diaminocyclohexane as ligands for the titanium(IV) alkoxide-promoted addition of diethylzinc to aldehydes

Chiral C₂-symmetric diphenylphosphoramide 4 and diphenylthiophosphoramide 5 were prepared from the reaction of diphenylphosphinic chloride and diphenylthiophosphinic chloride with (1R,2R)-(−)-1,2-diaminocyclohexane in the presence of diisopropylethylamine in high yields. They were used as chiral ligands in the catalytic asymmetric addition reaction of diethylzinc to aldehydes in the presence of titanium(IV) isopropoxide to give the corresponding sec-alcohols in 70–83% ee with an (R)-configuration and in 40–50% ee with an (S)-configuration, respectively.     

An Efficient Approach to the Synthesis of Lacto-N-Triosylceramide and Related Substances

Abstract

Hexatriosyl fluorides 3 and 4 were prepared from the known trisaccharides 8 and 13, respectively. These compounds were reacted with the sphingosine derivative 2 to afford coupled products 22 and 25 which, in turn, were converted into the protected glycosphingolipids 23 and 26 after reduction and acylation. Compound 2 was found to be a better substrate than the protected ceramide 1, which had been used previously. Compound 23 was transformed into the lacto-N-triosylceramide 24.     

An Alternative Approach to the Synthesis of Parvistone C

A stereoselective total synthesis of parvistone C, an oxygenated natural styryllactone, has been accomplished in excellent overall yield by employing asymmetric aldol reaction, asymmetric epoxidation and regioselective epoxide ring opening as the key steps. Our synthetic strategy is very simple, concise and no use of protecting groups.     

Synthesis of Novel C2—Symmetric Chiral Polyamide Macrocycles Containing Pyridyl Side—arm

Three novcl C2-symmetic macrocycles containing pyridyl units have been prepared by the cyclic condensation of chiral diamide intermediates with 2,6-pyridinedicarbonyl dichloride in highly diluted solution at room temperature.     

Into the Next Dimension: Nanometer-Sized, Oligonuclear Coordination Compounds with C(3)-Symmetric Ligands

Nanometer-sized cavities are present in oligonuclear coordination compounds formed in molecular self-assembly processes from C(3)-symmetric ligands and appropriate metal complex fragments. The structures obtained can be described as basic polyhedra such as tetrahedron, hexahedron, or octahedron (see picture).