Catalytic asymmetric hydrogenation to access spiroindane dimethyl acetic acid

Asymmetric hydrogenation of achiral spiroindene dimethyl acetic acid 2 with 4% of Ru(II)-Mandyphos in acetone produced (S)-spiroindane dimethyl acetic acid 1 in 86% isolated yield and 96.8:3.2 enantiomeric ratio.     

Asymmetric hetero-Diels–Alder reaction of 1-alkyl-3-silyloxy-1,3-dienes with ethyl glyoxylate catalyzed by a chiral (salen)cobalt(II) complex

The hetero-Diels–Alder reactions of 1-alkyl-3-(tert-butyldimethylsilyl)oxy-1,3-butadienes with ethyl glyoxylate catalyzed by chiral salen–metal complexes have been studied. With a cobalt(II) complex as the catalyst, the reaction of 1-(2-benzyloxyethyl)-3-(tert-butyldimethylsilyl)oxy-1,3-butadiene with ethyl glyoxylate gave the Diels–Alder product in 75% isolated yield with the endo:exo ratio >99:1 and the enantiomeric excess ≥52%. The effects of temperature, catalyst and solvent are also discussed.     

Synthesis and electrochemical behavior of inclusion complexes based on β-cyclodextrin and alkylaromatic compounds: Electrochemical carboxylation of the β-cyclodextrin-1-(4-isobutylphenyl)ethylchloride inclusion complex on a glassy-carbon cathode in anhydrous dimethylformamide

Inclusion complexes of β-cyclodextrin with alkylaromatic compounds β-cyclodextrin-1-(4-isobutylphenyl)ethylchloride in the “guest-host” molar ratio of 1 : 2 and β-cyclodextrin-methyl-(4-isobutylphenyl)ketone in the “guest-host” molar ratio of 1 : 1, are synthesized, isolated, and characterized. It is shown that preparative electrocarboxylation of the inclusion complex β-cyclodextrin-1-(4-isobutylphenyl)ethylchloride on a glassy-carbon cathode with a dissolving magnesium anode in dimethylformamide affords S-forms of 2-(4-isobutylphenyl)propionic acid (S-Ibuprofen) in a high enantiomeric excess (97%). In addition to the acid, a dimer and a hydride form from the corresponding intermediates.     

An efficient chemoenzymatic approach to (S)-gamma-fluoroleucine ethyl ester

[reaction: see text] An asymmetric synthesis of (S)-gamma-fluoroleucine ethyl ester 1 is described. The key transformation involves a lipase-catalyzed dynamic ring-opening of 2-(3-butenyl)azlactone 7b with EtOH to give amide ester (S)-6b in 84% enantiomeric excess. Removal of the N-pentenoyl group with N,N'-dibromodimethylhydantoin in the presence of trifluoroacetic acid afforded the titled compound, which was isolated as its hydrogen sulfate salt in 75% yield and >97% ee.     

Stereoselective chemoenzymatic synthesis of sitophilate: a natural pheromone

The aggregation pheromone of the granary weevil Sitophilus granarius, (2S,3R)-1-ethylpropyl 3-hydroxy-2-methylpentanoate, has been synthesized in 63% total isolated yield and high chemical and enantiomeric purity (98% de, >99% ee) from readily available methyl 3-oxopentanoate. A stereoselective ketone reduction followed by an ester hydrolysis, were the two key steps of the synthesis and were both performed by commercially available enzymes.     

Novel Chiral Bisformamide-Promoted Asymmetric Allylation of Benzaldehyde with Allyltrichlorosilane

Novel chiral bisformamides have been prepared from (R,R)-1,2-cyclohexanediamine and utilized as Lewis bases in the asymmetric allylation of benzaldehyde with allyltrichlorosilane. The reaction in the presence of Lewis base 1i gave an 83:17 enantiomeric ratio (R/S) of the products in 90% isolated yield.      

Catalytic SN2′‐ and Enantioselective Allylic Substitution with a Diborylmethane Reagent and Application in Synthesis

A catalytic method for the site‐ and enantioselective addition of commercially available di‐B(pin)‐methane to allylic phosphates is introduced (pin=pinacolato). Transformations may be facilitated by an NHC–Cu complex (NHC=N‐heterocyclic carbene) and products obtained in 63–95 % yield, 88:12 to >98:2 S_N2′/S_N2 selectivity, and 85:15–99:1 enantiomeric ratio. The utility of the approach, entailing the involvement of different catalytic cross‐coupling processes, is highlighted by its application to the formal synthesis of the cytotoxic natural product rhopaloic acid A.     

Production of l-tryptophan by enantioselective hydrolysis of d,l-tryptophanamide using a newly isolated bacterium

Bacterial strain ZJB-09211 capable of amidase production has recently been isolated from soil samples. The strain is able to asymmetrically hydrolyze l-tryptophanamide from d,l-tryptophanamide to produce l-tryptophan in high yield and with excellent stereoselectivity (enantiomeric excess > 99.9 %, and enantiomeric ratio > 200). Strain ZJB-09211 has been identified as Flavobacterium aquatile based on the cell morphology analysis, physiological tests, and the 16S rDNA sequence analysis. Optimization of the fermentation medium led to an about six-fold increase in the amidase activity of strain ZJB-09211, which reached 501.5 U L^?1. Substrate specifity and stereoselectivity investigations revealed that amidase of F. aquatile possessed a broad substrate spectrum and high enantioselectivity.     

Systematic Studies using 2‐(1‐Adamantylethynyl)pyrimidine‐5‐carbaldehyde as a Starting Material in Soai’s Asymmetric Autocatalysis

Herein, we present a new substrate for the Soai reaction, which has an adamantylethynyl residue ( 1 g ) and exhibits asymmetric autocatalysis, yielding products with enantiomeric excesses above 99 %. For the first time, all reactions were performed on a parallel synthesizer system to ensure identical reaction conditions. A detailed systematic study of reaction parameters was performed and we report the highest enhancements of enantiomeric excess reported so far in the Soai reaction in one reaction cycle (7.2→94.1 % ee or 3.1→92.1 % ee). Our results led to a set of reaction parameters that yield reproducible results. Therefore, our new starting material 1 g is suitable for systematic and mechanistic studies on this remarkable reaction. A series of experiments designed to quantify the amplification of enantiomeric excess demonstrated that the reaction can be used in principle as a tool for the detection of low enantiomeric excesses: under definite conditions, an unknown low enantiomeric excess (0.1–7 %) was amplified to a detectable one. A back calculation to the original value offers a new method for the determination of small enantiomeric excesses.     

Catalytic Enantioselective Synthesis of Allylic Boronates Bearing a Trisubstituted Alkenyl Fluoride and Related Derivatives

The first catalytic method for diastereo‐ and enantioselective synthesis of allylic boronates bearing a Z‐trisubstituted alkenyl fluoride is disclosed. Boryl substitution is performed with either a Z‐ or E‐allyldifluoride and is catalyzed by bisphosphine/Cu complexes, affording products in up to 99 % yield with >98:2 Z/E selectivity and 99:1 enantiomeric ratio. A variety of subsequent modifications are feasible, and notable examples are diastereoselective additions to aldehydes/aldimines to access homoallylic alcohols/amines containing a fluorosubstituted stereogenic quaternary center.     

Synthesis of (R)-alpha-benzylmethionine: a novel rearrangement during alkylation of the Seebach (R)-methionine oxazolidinone

Alkylation of the enolate of the Seebach (R)-methionine oxazolidinone with benzyl bromide gave the expected benzylated product in low yield. The major product was a novel amine arising from oxazolidinone cleavage, decarboxylation, alkylation and finally hydrolysis. The rearrangement could be suppressed by using a more reactive electrophile or by using the N-Cbz instead of the N-benzoyl protecting group, and the required (R)-alpha-benzyl-methionine was obtained in 78% yield and in an enantiomeric ratio of 90:10.     

Synthesis of 4-diphosphocytidyl-2-C-methyl-D-erythritol and 2-C-methyl-D-erythritol-4-phosphate

2-C-Methyl-D-erythritol 4-phosphate (MEP, 2) and 4-diphosphocytidyl-2-C-methyl-D-erythritol (CDPME, 3) are metabolites in the MEP pathway for biosynthesis of isoprenoid compounds in bacteria, plant chloroplasts, and algae. The free phosphoacid of 2 was prepared from benzyloxyacetone in five steps with an overall yield of 27% and an enantiomeric ratio (er) of 75:25. Following titration to the corresponding tributylammonium salt, 2 was coupled to cytidine 5'-monophosphate using a protocol originally developed for synthesis of base-sensitive nucleoside diphosphate sugars to give 3 in 40% yield, following purification by size exclusion chromatography.     

Total synthesis of (+)-cocaine via desymmetrization of a meso-dialdehyde

[reaction: see text] The total synthesis of (+)-cocaine is described. An extension of the recently reported proline catalyzed intramolecular enol-exo-aldol reaction to a meso-dialdehyde provided the tropane ring skeleton directly with good enantiomeric excess. The meso-dialdehyde was prepared using a 2-azaallyllithium [3 + 2] cycloaddition to generate a cis-2,5-disubstituted pyrrolidine. Overall, the synthesis proceeded in 6.5% yield and 86% ee over 14 linear steps starting from commercially available 3-benzyloxy-1-propanol.     

手性亚砜法合成粉 虫性信息素

5-氯-2-戊酮(2)经四步反应制得(R)-(+)-4-甲基-3-戊烯基对甲苯基亚砜(6), 化合物6与乙醛进行不对称加成反应得手性醇(7), 7经兰尼镍还原性脱硫反应即合成出目标产物粉 虫性信息素(1), 其光学纯度可达45%。     

Experimental determination of enantiomeric purity lower than 1% in the case of chiral secondary alcohols

Consider a secondary alcohol, of unknown enantiomeric purity p which reacts with excess of racemic α-phenylbutyric anhydride in a solution of pyridine. The ratio N between the number of reacting anhydride molecules and the number of alcohol molecules esterified can be evaluated by acidimetric titration. The proportions of diastereomeric esters are measured by CPV (or NMR) and we obtain the asymmetric induction Q. The optical purity P of the α-phenylbutyric acid isolated is determined by a polarimetric reading.We have established simply a relationship p = P(2N - 1)/Q which allows the enantiomeric purity to be calculated. This method is used with success, in cases of very low enantiomeric purity (<1%).The experimental results prove its efficiency.     

Catalytic Asymmetric Alkylation of Acylsilanes

The highly enantioselective addition of Grignard reagents to acylsilanes is catalyzed by copper diphosphine complexes. This transformation affords α‐silylated tertiary alcohols in up to 97 % yield and 98:2 enantiomeric ratio. The competing Meerwein–Ponndorf–Verley reduction is suppressed by the use of a mixture of Lewis acid additives. The chiral catalyst can be recovered as a copper complex and used repeatedly without any loss of catalytic activity.     

Electronically Activated Organoboron Catalysts for Enantioselective Propargyl Addition to Trifluoromethyl Ketones

A broadly applicable, practical, scalable, efficient and highly α‐ and enantioselective method for addition of a silyl‐protected propargyl moiety to trifluoromethyl ketones has been developed. Reactions, promoted by 2.0 mol % of a catalyst that is derived in situ from a readily accessible aminophenol compound at ambient temperature, were complete after only 15 minutes at room temperature. The desired tertiary alcohols were isolated in up to 97 % yield and 98.5:1.5 enantiomeric ratio. Alkyl‐, alkenyl‐, alkynyl‐, aryl‐ or heteroaryl‐substituted trifluoromethyl ketones can be used. Utility is highlighted by application to a transformation that is relevant to enantioselective synthesis of BI 653048, a compound active against rheumatoid arthritis.     

Site- and enantioselective formation of allene-bearing tertiary or quaternary carbon stereogenic centers through NHC-Cu-catalyzed allylic substitution

Catalytic enantioselective allylic substitutions that result in addition of an allenyl group (<2% propargyl addition) and formation of tertiary or quaternary C-C bonds are described. Commercially available allenylboronic acid pinacol ester is used. Reactions are promoted by a 5.0-10 mol % loading of sulfonate-bearing chiral bidentate N-heterocyclic carbene (NHC) complexes of copper, which exhibit the unique ability to furnish chiral products arising from the S(N)2' mode of addition. Allenyl-containing products are generated in up to 95% yield, >98% S(N)2' selectivity, and 99:1 enantiomeric ratio (er). Site-selective NHC-Cu-catalyzed hydroboration of enantiomerically enriched allenes and conversion to the corresponding β-vinyl ketones demonstrates the method's utility.     

Asymmetric diels - alder reacrions with α-chloronitroso compounds- II. The use of a carbohydrate derived α-chloro-α-nitroso ether

The Diels-Alder reaction of 1,3-cyclohexadiene with the α-chloro-α-nitroso ether 2, prepared from mannose via the lactone oxime 1, gives the adduct 3 with 1-(S),4-(R) configuration in 69 % chemical yield and ? 95 % enantiomeric excess.     

Direct catalytic asymmetric Michael reaction of hydroxyketones: asymmetric Zn catalysis with a Et2Zn/linked-BINOL complex

Full details of our direct Michael addition of unmodified ketones using new asymmetric zinc catalysis are described. Et(2)Zn/(S,S)-linked-BINOL complexes were successfully applied to direct 1,4-addition reactions of hydroxyketones. The first generation Et(2)Zn/(S,S)-linked-BINOL 1 = 2/1 system was effective for 1,4-addition of 2-hydroxy-2'-methoxyacetophenone (3). Using 1 mol % of (S,S)-linked-BINOL 1 and 2 mol % of Et(2)Zn, we found that a 1,4-addition reaction of beta-unsubstituted enone proceeded smoothly at 4 degrees C to afford products in high yield (up to 90%) and enantiomeric excess (up to 95%). In the case of beta-substituted enones, however, the first generation Et(2)Zn/(S,S)-linked-BINOL 1 = 2/1 system was not at all effective. The second generation Et(2)Zn/(S,S)-linked-BINOL 1 = 4/1 with MS 3A system was developed and was effective for various beta-substituted enones to afford products in good dr, yield (up to 99%), and high enantiomeric excess (up to 99% ee). With the Et(2)Zn/1 = 4/1 systems, catalyst loading for beta-unsubstituted enone was reduced to as little as 0.01 mol % (substrate/chiral ligand = 10 000). The new system was also effective for 1,4-addition reactions of 2-hydroxy-2'-methoxypropiophenone (9) to afford chiral tert-alcohol in high enantiomeric excess (up to 96% ee). Mechanistic investigations as well as transformations of the Michael adducts into synthetically versatile intermediates are also described.