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1.
Catalytic asymmetric aza Diels-Alder reactions of acylhydrazones with Danishefsky’s dienes have been developed. A chiral zirconium complex derived from zirconium propoxide and 3,3′,6,6′-I4BINOL was found to be effective in this reaction, and the desired optically active 2,3-dihydro-4-pyridone derivatives were obtained with high enantioselectivities. Asymmetric formal synthesis of a natural product, coniine, was conducted using this catalytic asymmetric reaction as a key step.  相似文献   

2.
Cationic palladium (Pd)- and platinum (Pt)-phosphinooxazolidine catalysts 13a-c, 15a-d, 17a-c, and 19a-c were prepared from phosphinooxazolidine ligands 1-3, MCl(2) (M = Pd and Pt), and counterions, and the activities of the catalysts in the asymmetric Diels-Alder (DA) reactions of cyclic or acyclic dienes with imide dienophiles were investigated. These catalysts demonstrated high levels of catalytic activity. The cationic Pd-POZ complex 13c provided particularly excellent enantioselectivity (98% ee) in the DA reactions of cyclopentadiene with acryloyl-, crotonyl-, and fumaroyl-1,3-oxazolidin-2-ones (20a-c).  相似文献   

3.
Chiral N-heterocyclic carbene (NHC) catalyzed redox reactions of racemic alpha-chloroaldehydes lead to the generation of chiral enolates suitable for highly enantioselective inverse-electron-demand 1-oxodiene Diels-Alder reactions. Significantly, these reactions proceed under mild, operationally friendly reaction conditions (EtOAc, room temperature, 2-8 h) using less than 1 mol % of a chiral N-mesityl triazolium salt as the precatalyst. A broad array of densely functionalized dihydropyran-2-ones bearing either aliphatic or aromatic substiutents are formed in excellent yields and exceptional enantioselectivities from readily available reactants. Stereochemical mismatching between the racemic starting materials and the chiral catalyst is avoided by rapid epimerization of the chloroaldehydes under the reaction conditions.  相似文献   

4.
Haifeng Du 《Tetrahedron》2005,61(40):9465-9477
This paper describes the successful development of a series of chiral zinc catalysts containing (R)-3,3′-Br2-BINOL ligand and various diimine activators for enantioselective HDA reaction of Danishefsky's diene with aldehydes through a combinatorial approach, affording the corresponding 2,3-dihydro-4H-pyran-4-one derivatives in excellent yields and enantioselectivities. The application of this type of catalysts was also extended to the diethylzinc addition to the benzaldehyde, affording the corresponding secondary alcohol with up to 94.5% ee under optimized conditions. On the basis of these facts, the integration of two distinct enantioselective reactions, HDA and diethylzinc addition reactions, has been realized in one-pot with the promotion of a single chiral zinc catalyst in a sequential manner. The impact of diimine additive on the catalytic system of HDA reaction was also investigated by probing the nonlinear effect of reaction system. The positive nonlinear effect exhibited in the catalytic system could be attributed to the poor solubility of the heterochiral zinc species. On the basis of various experimental findings disclosed in this research, a possible mechanism for the asymmetric induction in the 3,3′-Br2-BINOL/Zn/diimine catalyzed enantioselective HDA reaction of Danishefsky's diene with aldehydes was outlined.  相似文献   

5.
The discovery of a novel activation mode provided by organocatalysis is presented. It is demonstrated that the merger of optically active secondary amines and polyenals generates reactive trienamine intermediates, which readily participate in Diels-Alder reactions with different classes of dienophiles, hence, providing a facile entry to highly complex molecular frameworks with excellent stereocontrol. For the Diels-Alder reactions with 3-olefinic oxindoles, spirocyclic oxidoles are formed in high yields, and with enantioselectivities in the range of 94-98% ee. It is demonstrated, that some of these products can be transformed into the hexahydrofuro[2,3-b]indole fragment. The organocatalytic trienamine concept has been extended to also include Diels-Alder reactions of olefins substituted with cyanoacetates providing multifunctional cyclohexenes with three contiguous stereocenters in high yield and good stereocontrol. The novelty of this activation strategy lies within the perfect chirality relay over a distance of up to eight bonds. Moreover, we also present the first trienamine tandem reaction by combining trienamine catalysis with enamine activation. In addition to the experimental results, a detailed mechanistic survey is also provided including NMR spectroscopic studies and calculations of the reactive trienamine intermediates, rationalizing the origin of stereochemistry.  相似文献   

6.
Wang resin-bound intermediates derived from Fmoc-L-phenylalaninal and Fmoc-L-valinal, and a resin supported Horner-Wadsworth-Emmons reaction, were treated with cinnamaldehyde derivatives, acetic acid, and borohydride to give secondary amines which were subsequently benzoylated to afford various derivatives of 3. Heating 3 at 95 degrees C induced cycloaddition reactions and produced 4 as the major product. Compounds 3 which were derived from 4-methoxycinnamaldehyde were more reactive, but did not give 4 and 4-7g. The direct cleavage of 3b using TFA led to the isolation of cycloaddition-demethylation product 10. The derivative of 3, which contained an electron-withdrawing nitro group on the phenyl ring, produced a single diastereomer of 4. The Diels-Alder cycloaddition between two electron-deficient counterparts showed similar reactivity to that of the reactions which have a normal complementary electron-demand.  相似文献   

7.
Direct asymmetric aldol reactions of aldehydes with ketones in the presence of a catalytic amount of sulfonamide 4 and trifluoroacetic acid afforded the corresponding anti-aldol products in moderate to excellent yields with 85-93% ee.  相似文献   

8.
[reaction: see text] The first catalytic, asymmetric 2,3-trans-selective hetero Diels-Alder reaction has been developed. The reactions of aldehydes with Danishefsky's dienes proceeded smoothly to afford the pyranone derivatives in high yields with high trans-selectivities and enantioselectivities in the presence of a chiral zirconium complex, which was prepared from zirconium tert-butoxide and (R)-3,3'-diiodobinaphthol or its derivatives, primary alcohol, and a small amount of water. This reaction was applied to the concise synthesis of (+)-prelactone C.  相似文献   

9.
10.
The low-temperature periodical activation of the catalysts based on the metal complexes of nitrogen-containing carbon is observed in the course of isopropylbenzene oxidation. The concentration of the surface hydroperoxide groups responsible for the chain process affects both catalyst deactivation and reactivation. Possible reactions responsible for the deactivation and periodical activation of the catalyst are considered.  相似文献   

11.
Two- or three-component aza Diels-Alder reactions of Danishefsky's diene with imines or aldehydes and amines in water took place smoothly under neutral conditions in the presence of a catalytic amount of an alkaline salt such as sodium triflate to afford dihydro-4-pyridones in high yields.  相似文献   

12.
The studies performed with chiral oxazolines as vehicles for a number of C-C bond-forming reactions are traced back to the early 1970s. The main source of chirality in these studies was derived from chiral, nonracemic amino alcohols which, themselves, were prepared from amino acids. The formation of chiral oxazolines from these materials provided interesting and useful starting materials for these studies.The factors responsible for high optical yields during that era were attributed to rigidity or precomplexation of the reactants, thus providing a more well-defined topography during the reaction course. A number of C-C bond reaction types are described including alkylations, additions, and organometallic reactions. The ee's of many of the products arrived at are well above 90%. This level of ee was virtually unprecedented in the early to mid 1970s. In addition to the synthetic emphasis, several mechanistic questions, arising in other areas, were also undertaken due to the accessibility of the appropriate requisite chiral materials.  相似文献   

13.
A novel family of chiral imidazolium-based ionic liquids containing a chiral moiety and a free hydroxyl function has been designed and synthesized using isosorbide as a biorenewable substrate. These chiral ionic liquids were found to catalyze the aza Diels-Alder reaction to give good yields and moderate diastereoselectivities. Chiral ionic liquids are recycled while their efficiency is preserved.  相似文献   

14.
Sarakinos G  Corey EJ 《Organic letters》1999,1(11):1741-1744
[formula: see text] The enantiomerically pure hydroxy sulfones (+)- and (-)-2 have been prepared from 1,2-epoxycyclohexane by a simple and practical procedure. The acrylate esters of these alcohols undergo BCl3-catalyzed Diels-Alder reactions with a variety of dienes at -78 to -55 degrees C in CH2Cl2 or C7H8 with high dienophile face selectivity (Table 1). The chiral esters so formed are readily cleaved with recovery of the controllers (+)- or (-)-2. Esters of (+)- and (-)-2 can be converted to Z-potassium enolates and alkylated with high face selectivity.  相似文献   

15.
Markedly enhanced recyclability of osmium catalyst in asymmetric dihydroxylation has been achieved by using osmylated macroporous resins bearing both residual vinyl groups and quaternary ammonium moiety.  相似文献   

16.
Bis-trifluoromethanesulfonylamide (bis-triflylamide) itself works as an efficient chiral Brønsted acid catalyst for the hetero Diels-Alder reactions between Danishefsky’s diene and glyoxylate or phenylglyoxal presumably through double hydrogen bonding.  相似文献   

17.
Bis-sulfonamides are demonstrated to be promising candidates for the efficient activation of carbonyl compounds through hydrogen bonding. Exemplified by three carbonyl addition reactions: Mukaiyama-aldol, hetero Diels-Alder and Friedel-Crafts reactions we show that bis-triflamides or bis-nonaflamides of commercially available chiral diamines act as chiral Br?nsted-acid catalysts, leading to the optically active products in moderate to excellent yields and with enantioselectivities up to 73% ee.  相似文献   

18.
Ariel M. Sarotti 《Tetrahedron》2009,65(17):3502-3028
Chiral alcohols were designed and easily prepared from levoglucosenone, a biomass-derived valuable synthon. These alcohols were tested as chiral auxiliaries in asymmetric Diels-Alder reactions between the corresponding acrylates with acyclic and cyclic dienes. The regio, stereo, and facial selectivity varied from very good to excellent, depending upon the benzylic substitution of the auxiliary and the diene employed. As a consequence, after removal of the auxiliary, the resulting carboxylic acid derivatives were obtained in 72-99% ee.  相似文献   

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