AlPO-Catalysed asymmetric Diels-Alder reactions of cyclopentadiene with chiral acrylates

Reactions of cyclopentadiene with several chiral acrylates are studied and compared with the same reactions catalysed by Zn(II)-exchanged K10 montmorillonite. In general, amorphous AlPO₄ is a more efficient catalyst than the clay. In particular, the reaction of cyclopentadiene with (−)-8-phenylmenthyl acrylate leads to 74% diastereomeric excess (d.e.) in methylene chloride at low temperatures. This result constitutes the highest asymmetric induction described to date for a solid-catalysed asymmetric Diels-Alder reaction. When the reactions are carried out in the absence of a solvent a noticeable decrease in selectivity is observed, probably due to an extensive competition of the non-catalysed reaction.     

High asymmetric induction in diels-alder additions of cyclopentadiene to acrylates derived from isoborneol

Starting from (R)-(+)- and from (S)-(?)-camphor the chiral alcohols $\text{1}$, $\text{2}$ and $\text{3}$ have been prepared; their acrylates II underwent TiCl₂(OR)₂-promoted Diels-Alder additions to cyclopentadiene giving efficiently in a predictable manner either the (2R)- or the (2S)-adducts III with up to virtually quantitative asymmetric induction.     

手性胶束的不对称诱导作用不对称苯偶姻缩合反应

胶束体系是模拟酶的简单模型之一。手性胶束对反应有手性诱导作用。在表面活性剂(1R，2S)-(-)-N-十二烷基-N-甲基麻黄素溴化物和(1R，2S)-(-)-N-十六烷基-N-甲基麻黄素溴化物形成的胶束体系中进行的苯偶姻缩合反应，生成了光学活性的α-羟基酮。     

Chiral phosphinothiourea-catalyzed asymmetric Morita-Baylis-Hillman reactions of acrylates with aromatic aldehydes

A series of chiral bifunctional phosphinothioureas were synthesized and applied to the enantioselective Morita-Baylis-Hillman reaction of aromatic aldehydes with acrylates. In the presence of 8 mol % of organocatalyst 2e, the Baylis-Hillman adducts were obtained in good enantioselectivities and up to 96% yield under mild reaction conditions.     

Preparation,structure and asymmetric diels-alder reactions of 10-arylsulfonylisobornyl acrylates

The crystalline chiral auxiliaries 4 and 5 were readily prepared from camphorsulfonic acid. Their acrylates underwent the diels-alder reactions 6 → 7 with modest asymmetric induction consistent with an X-ray study of $\text{6a}$.     

Amplification of asymmetric induction in sequential reactions of bis-diazoacetates catalyzed by chiral dirhodium(II) carboxamidates

[reaction: see text] Two sequential intramolecular carbon-hydrogen insertion or cyclopropanation reactions of bis-diazoacetates using chiral dirhodium(II) carboxamidate catalysts are reported. The initial metal carbene transformation forms an excess of one enantiomer that with the second transformation further enhances stereocontrol (kinetic amplification). Diastereoselectivity and enantioselectivity for product formation are controlled by the catalyst.     

Asymmetric induction in thia-Diels-Alder reactions of chiral polyfluoroalkylthionocarboxylates

A series of chiral S- or O-alkyl thionoesters have been synthesized by treatment of trifluorothioacetyl- or 2,2,3,3-tetrafluorothiopropionyl chloride with corresponding thiols or alcohols. The thia-Diels-Alder reaction of the thionoesters with symmetrical 1,3-dienes proceeds with diastereoselectivity up to 60%. Structures of cycloaddition products and corresponding transition states have been studied at the DFT level of approximation. The experimentally observed diastereomeric excess has been referred to differences in activation energies of transition states, preceding formation of the diastereomeric cycloaducts.     

A sulfur-containing diselenide as an efficient chiral reagent in asymmetric selenocyclization reactions

Treatment of the di-2-[(1S)-1-(methylthio)ethyl]phenyl diselenide with bromine and silver triflate afforded the corresponding selenyl triflate which was used in situ as a strongly electrophilic selenium reagent to effect the asymmetric synthesis of oxygen- or nitrogen-containing heterocycles. Cyclic ethers, lactones, lactams or N-protected pyrrolidines have been prepared in good yield with complete regioselectivity and high diastereoselectivity.     

Oxazolidinones as chiral auxiliaries in asymmetric aldol reactions applied to total synthesis

Asymmetric aldol reactions of oxazolidinones as chiral auxiliaries have been achieved and attracted significant consideration as one of the most powerful synthetic tools for the carbon–carbon bond-forming reactions. The methodology has been highly successful in the stereoselective construction of a number of natural products, antibiotics, and other medicinally important compounds. The present review is focused on the utility and versatility of oxazolidinones (Evans chiral auxiliaries) in the asymmetric aldol condensations for the total synthesis of natural products and complex targets.     

Modular chiral thiazolidine catalysts in asymmetric aryl transfer reactions

Modular chiral thiazolidine derivatives were synthesized in a single step from inexpensive and commercially available starting materials. These ligands catalyzed enantioselective arylation of different aldehydes using aryl boronic acids as a source of transferable aryl groups. The products were obtained in excellent yields and good enantioselectivities.     

A practical new chiral controller for asymmetric Diels-Alder and alkylation reactions

[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.     

Synthesis of chiral sulfonylmethyl isocyanides,and comparison of their propensities in asymmetric induction reactions with acetophenones1

Seven chiral analogues of tosylmethyl isocyanide (TosMIC) were synthesized in order to investigate and compare their ability to achieve asymmetric induction in base mediated reactions with acetophenone and trifluoroacetophenone. Acid hydrolysis of the intermediate 2-oxazolines (10 and 11) gave optically active α-hydroxy aldehydes (12 and 13).     

A novel (S)-proline-modified task-specific chiral ionic liquid—an amphiphilic recoverable catalyst for direct asymmetric aldol reactions in water

A novel chiral (S)-proline-modified task-specific ionic liquid has been designed and synthesized as an efficient recoverable organocatalyst for the direct asymmetric aldol reaction between cycloalkanones and aromatic aldehydes in the presence of water. The catalyst retains its activity and selectivity over at least five reaction cycles.     

Development of catalytic asymmetric reactions via chiral palladium enolates

This article describes the generation of chiral palladium enolates and their application to several kinds of catalytic asymmetric reactions. Two methods to generate chiral enolates were developed using novel cationic palladium complexes 1 and 2 . In these processes, water or a hydroxo ligand on palladium metal plays an important role as a nucleophile to promote the transmetallation or as a Brønsted base to abstract an acidic α‐proton of the carbonyl group. These enolates showed sufficient reactivity with various electrophiles. Using a chiral Pd enolate as a key intermediate, highly enantioselective reactions such as catalytic aldol reactions, Mannich‐type reactions, Michael reactions, and fluorination reactions were developed. The unique structures of the palladium enolate complexes were elucidated and reaction mechanisms are proposed. © 2004 The Japan Chemical Journal Forum and Wiley Periodicals, Inc. Chem Rec 4: 231–242; 2004: Published online in Wiley InterScience ( www.interscience.wiley.com ) DOI 10.1002/tcr.20017     

手性金属催化剂在不对称环丙烷化反应中的应用进展

手性金属催化剂在不对称环丙烷化反应中的应用一直是不对称合成领域的一个热点。对三十多年来的这一领域的手性金属催化剂的发展作了详细的归纳和评述。     

Second generation levoglucosenone-derived chiral auxiliaries. Scope and application in asymmetric Diels-Alder reactions

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.     

Combinatorial approach to the asymmetric hydrogenation of β-acylamino acrylates: use of mixtures of chiral monodentate P-ligands

The previously proposed concept of using mixtures of two different chiral monodentate P-ligands has been extended to the asymmetric Rh-catalyzed hydrogenation of β-acylamino acrylates with formation of chiral β-amino acid derivatives. Mixtures of BINOL-derived phosphites and phosphonites are particularly effective (ee=94-99% for five different substrates).     

Recent advances in asymmetric reactions catalyzed by chiral phosphoric acids

The very recent advances in chiral phosphoric acids (CPAs) catalyzed asymmetric reactions are discussed.