Highly Enantioselective Microbial Hydrolysis of cis‐2‐Arylcyclopropanecarbonitriles

Hydrolysis of racemic cis‐2‐arylcyclopropanecarbonitriles catalyzed by Rhodococcus sp. AJ270 whole cells proceeded enantioselectively to afford the corresponding amide and acid with enantiomeric excess higher than 99%.     

Asymmetric conjugate addition reaction using pyrazole derivatives as a chiral catalyst

The conjugate addition of Grignard reagent ( 2 ) onto 1‐α,β‐unsaturated)acyl 3,5‐dimethylpyrazole ( 1 ) was enantioselectively catalyzed by the copper complex from cuprous compounds and 3‐phenyl‐l‐mentho‐pyrazole ( 3 ).     

Enantioselective Inclusion Complexation of N‐Nitrosopiperidines by Steroidal Bile Acids

N ‐nitrosamines , whose chirality is solely due to hindered rotation about the N−N bond, are enantioselectively enclathrated by the crystal host matrices of cholic or deoxycholic acid, as evidenced by X‐ray crystallography (see structure in picture) and CD spectra.     

Asymmetric reduction of aminoketones with borane and chiral oxazaborolidine catalyst

A group of α‐ and β‐N, N‐dialkyl amino ketones were reduced enantioselectively by 2 moles of borane‐tetrahydrofuran in the presence of 10 mol% of the in‐situ formed chiral oxazaborolidine, followed by diluted hydrochloric acid. The resulting amino alcohol‐borane complexes were treated with hydrogen chloride‐glycol‐methanol to give the optically active amino alcohol with the ee up to 99%.     

(–)‐epi‐Inosose‐2

The structure of the title compound, C₆H₁₀O₆, was determined to confirm the position of the keto group in the mol­ecule prepared enantioselectively by a bioconversion from myo‐inositol. There are two independent mol­ecules showing similar geometry.     

Isolation of lipase producer and its performance in enantioselective hydrolysis of glycidyl butyrate

A racemic glycidyl butyrate resolving strain, preliminarily identified as a Rhizopus sp., had been isolated from soil. Its extracellular lipase was found to enantioselectively hydrolyze the (S)-enantiomer of the chiral ester, with optimal activities at pH 5.3 and 42°C. Higher en antioselectivity of theenzyme was observed at lower temperatures, while the best anantioselectivity was obtained at pH 5.5–6.0, with an, E value (enantiomeric ratio) of 57.     

Enantioselective Synthesis of Ipsenol and Ipsdienol Using a (2-Bromoallyl)borane Derivative

(S)-(-)-Ipsenol (2b) and (S)-(+)-ipsdienol (4b), a major component of the sex pheromone of the bark beetle, and their enantiomers (3b and 5b) were prepared enantioselectively using tartrate esters of (2-bromoallyl)boronic acid in the key step.

     

Enzymatic Desymmetrising Redox Reactions for the Asymmetric Synthesis of Biaryl Atropisomers

Atropisomeric biaryls carrying ortho‐hydroxymethyl and formyl groups were made enantioselectively by desymmetrisation of dialdehyde or diol substrates. The oxidation of the symmetrical diol substrates was achieved using a variant of galactose oxidase (GOase), and the reduction of the dialdehydes using a panel of ketoreductases. Either M or P enantiomers of the products could be formed, with absolute configurations assigned by time‐dependent DFT calculations of circular dichroism spectra. The differing selectivities observed with different biaryl structures offer an insight into the detailed structure of the active site of the GOase enzyme.     

Regio- and Enantioselective Prenyl Anion Transfer: Application to the Total Synthesis of (−)-Rosiridol

At elevated temperature (refluxing THF) prenyl anion adds regio- and enantioselectively to aldehyde 1 when a chiral, borneol-derived ligand is present. This reaction is the key stepin the first total synthesis of the monoterpene (−)-rosiridol (retrosynthesis is shown on the right). In addition, the absolute configuration of this natural product has been assigned conclusively. M=Zn, R=tBuMe₂Si.     

Enantioselective Synthesis of C−N Axially Chiral N‐Aryloxindoles by Asymmetric Rhodium‐Catalyzed Dual C−H Activation

The first enantioselective Satoh–Miura‐type reaction is reported. A variety of C?N axially chiral N‐aryloxindoles have been enantioselectively synthesized by an asymmetric rhodium‐catalyzed dual C?H activation reaction of N‐aryloxindoles and alkynes. High yields and enantioselectivities were obtained (up to 99 % yield and up to 99 % ee). To date, it is also the first example of the asymmetric synthesis of C?N axially chiral compounds by such a C?H activation strategy.     

Asymmetric reaction of diethylzinc with aldehydes catalyzed by l‐menthopyrazole derivatives

N‐Hydroxyalkyl‐1‐menthopyrazoles acted as a chiral catalyst for the diethylzinc ( 1 ) addition to aromatic aldehydes, and 1‐aryl‐1‐propanols were afforded enantioselectively. These reactions were carried out optimally in toluene at 40 °C in the presence of 30 mol% of (2′S)‐2‐(2‐phenyl‐2‐hydroxyethyl)‐3‐phenyl‐1‐men‐thopyrazole ((S)‐ 16d ) to afford optically active 1‐aryl‐1‐propanols up to 70% ee (S).     

Asymmetric Diels–Alder Reaction of α‐Substituted and β,β‐Disubstituted α,β‐Enals via Diarylprolinol Silyl Ether for the Construction of All‐Carbon Quaternary Stereocenters

The asymmetric Diels–Alder reaction of α‐substituted acrolein proceeds in the presence of the trifluoroacetic acid salt of trifluoromethyl‐substituted diarylprolinol silyl ether to afford the exo‐isomer with both excellent diastereoselectivity and high enantioselectivity. In the Diels–Alder reaction of a β,β‐disubstituted α,β‐unsaturated aldehyde, good exo‐selectivity and excellent enantioselectivity was obtained when the perchloric acid salt of the bulky triisopropyl silyl ether of trifluoromethyl substituted diarylprolinol was employed as an organocatalyst in the presence of water. In both cases, all‐carbon quaternary stereocenters are constructed enantioselectively.     

Enantioselective Visible‐Light‐Mediated Formation of 3‐Cyclopropylquinolones by Triplet‐Sensitized Deracemization

3‐Allyl‐substituted quinolones undergo a triplet‐sensitized di‐π‐methane rearrangement reaction to the corresponding 3‐cyclopropylquinolones upon irradiation with visible light (λ=420 nm). A chiral hydrogen‐bonding sensitizer (10 mol %) was shown to promote the reaction enantioselectively (88–96 % yield, 32–55 % ee). Surprisingly, it was found that the enantiodifferentiation does not occur at the state of initial product formation but that it is the result of a deracemization event. The individual parameters that control the distribution of enantiomers in the photostationary state have been identified.     

Whole Cells in Enantioselective Reduction of tert-Butyl Acetoacetate

The β-ketoester tert-butyl acetoacetate was enantioselectively reduced to tert-butyl (S)-3-hydroxybutanoate by seven microorganism strains. The best result using free cells was obtained with the yeast R. rubra, which furnished 97.6% ee and higher than 99% of conversion within 24 h. After immobilization in calcium alginate spheres, R. rubra furnished 96% ee and higher than 99% ee within 24 h, even if substrate concentration was 58 mM. Immobilized cells were reused three times without loss of enantioselectivity.     

Asymmetric diels alder reaction using pyrazole derivatives as a chiral catalyst

N‐Acylpyrazoles ( 1 ) were promising as good dienophiles, which were easily converted into the desired carboxylic derivatives. Bis(pyrazolyl)methanes, which were derived from chiral pyrazoles, showed the activity of chiral catalyst. Particularly 10 mol% of bis(isomenthopyrazol‐1,1′‐yl)methane ( 8a ) catalyzed enantioselectively the Diels Alder reaction up to 40 % ee by the formation of complex with Mg(ClO₄)_2.     

δ‐Peptide Analogues of Pyranosyl‐RNA,Part 1 , Nucleo‐δ‐peptides Derived from Conformationally Constrained Nucleo‐δ‐amino Acids: Preparation of Monomers

Cyclic nucleo‐δ‐amino acids that constitute monomers of a conformationally constrained nucleo‐δ‐peptide base‐pairing system have been prepared. Their synthesis starts with an enantioselectively catalyzed chirogenic Diels‐Alder reaction, proceeds via a regioselective ε‐iodolactamization process, and ends with a regio‐ as well as diastereoselective introduction of nucleobases through S_N2‐type opening of a transiently formed N‐acylaziridine ring. Extensive use of X‐ray crystal‐structure analysis has been made to support structure assignments.     

Enantioselective scavenging using homogenate of Rhodotorula graminis: a facile preparation of d-amino acid derivatives in enantiopure form

An enantioselective scavenger (ES) comprised homogenate of Rhodotorula graminis containing multiple enzymes can enantioselectively remove l-enantiomer in a racemic mixture of amino acid derivatives (AADs), yielding d-enantiomer in high ee. Thirteen non-proteinogenic AADs were produced in enantiopure d form. The method appears to be an efficient cleaning and preparative strategy which can be applied to the production of d-AADs in high ee by enantioselectively scavenging the ‘l-contaminants’.     

Rhodium‐Catalyzed Asymmetric Cycloisomerization and Parallel Kinetic Resolution of Racemic Oxabicycles

While desymmetrizations by intermolecular asymmetric ring‐opening reactions of oxabicyclic alkenes with various nucleophiles have been reported over the past two decades, the demonstration of an intramolecular variant is unknown. Reported herein is the first rhodium‐catalyzed asymmetric cycloisomerization of meso‐oxabicyclic alkenes tethered to bridgehead nucleophiles, thus providing access to tricyclic scaffolds through a myriad of enantioselective C?O, C?N, and C?C bond formations. Moreover, we also demonstrate a unique parallel kinetic resolution, whereby racemic oxabicycles bearing two different bridgehead nucleophiles can be resolved enantioselectively.     

(−)-Sparteine-Mediated Asymmetric Intramolecular Carbolithiation of Alkenes: Synthesis of Enantiopure Cyclopentanes with Three Consecutive Stereogenic Centers

An asymmetric intramolecular carbolithiation reaction was developed by combining the (−)-sparteine-mediated enantiotopos-differentiating deprotonation and the anionic 5-exo-trig cyclization. Achiral 6-phenylhex-5-enyl carbamates were efficiently cyclized furnishing regio-, diastereo- (dr >99 : 1), and enantioselectively (er >98 : 2) 1,2-trans-substituted cyclopentanes. The intermediate primary benzylic lithium-carbanion pairs were – in spite of their configurative lability – diastereoselectively substituted by versatile electrophiles creating a third consecutive stereogenic center. Additionally, some 4-functionalized 6-phenylhex-5-enyl carbamates were also cyclized in high yield to provide enantiomerically pure cyclopentanes incorporating three adjacent stereogenic centers.     

以手性相转移催化剂为配体的单分子Cu (II)配合物及其不对称催化反应

在加热条件下,手性相转移催化剂氯化- N -（4-乙烯基苄基）辛可尼定（L1）与氯化铜在2-丁醇中反应,可得到一个单一手性的二价铜单分子配合物 N -（4-乙烯基苄基）辛可尼定三氯化铜(1)。配合物（1）和配体(L1)都可用于催化 N -（二苯基亚甲基）氨基乙酸叔丁基酯（3）烷基化反应,催化结果表明：使用配合物N-（4-乙烯基苄基）辛可尼定三氯化铜的反应对映体选择性比使用配体的更高,配合物催化能力的提高可能与配合物中喹啉环的N原子与铜配位、分子刚性增加有关。