Highly enantioselective synthesis of (R)-alpha-alkylserines via phase-transfer catalytic alkylation of o-biphenyl-2-oxazoline-4-carboxylic acid tert-butyl ester using cinchona-derived catalysts

[reaction: see text] A highly enantioselective synthetic method for (R)-alpha-alkylserines was developed by the phase-transfer catalytic alkylation of o-biphenyl-2-oxazoline-4-carboxylic acid tert-butyl ester (4i) using cinchona-derived phase-transfer catalyst N(1)-(9-anthracenylmethyl)-O(9)-allyl-dihydrocinchonidinium bromide (up to 96% ee).     

Highly enantioselective phase-transfer catalytic alkylation in the preparation of non-natural alpha-amino acids via solid phase synthesis using aldimine linker

A new Merrifield-resin-derived glycinimine tert-butyl ester (9) was prepared and applied to the enantioselective synthesis of non-natural alpha-amino acids. High enantioselectivities (86 to >99% ee) were accomplished by employing the aldimine linker under phase-transfer alkylation conditions, using 50% aqueous CsOH in toluene/chloroform (7:3) at 0 degrees C in the presence of N-(9-anthracenylmethyl)-O(9)-allylcinchonidium bromide (10 mol %).     

Enantioselective synthesis of (R)- and (S)-alpha-alkylcysteines via phase-transfer catalytic alkylation

We reported efficient enantioselective synthetic methodologies for (R)-alpha-alkylcysteines and (S)-alpha-alkylcysteines. The phase-transfer catalytic alkylation of 2-phenyl-2-thiazoline-4-carboxylic acid tert-butyl ester and 2-o-biphenyl-2-thiazoline-4-carboxylic acid tert-butyl ester, in the presence of chiral catalysts (1 or 2), gave the corresponding alkylated products, which could be hydrolyzed to provide (R)-alpha-alkylcysteines (67->99% ee) and (S)-alpha-alkylcysteines (66-88% ee), respectively.     

Highly enantioselective synthesis of (2S)-alpha-(hydroxymethyl)-glutamic acid by the catalytic Michael addition of 2-naphthalen-1-yl-2-oxazoline-4-carboxylic acid tert-butyl ester

[reaction: see text]. Highly enantioselective synthesis of a potent metabotropic receptor ligand, (2S)-alpha-(hydroxymethyl)-glutamic acid (2, HMG) was accomplished by the catalytic Michael addition of 2-naphthalen-1-yl-2-oxazoline-4-carboxylic acid tert-butyl ester (3b), using the phosphazene base, BEMP, in CH(2)Cl(2) at -60 degrees C in the presence of (S)-binaphthyl quaternary ammonium salt 4.     

First asymmetric total synthesis of (-)-antofine by using an enantioselective catalytic phase transfer alkylation

[structure: see text] The first asymmetric total synthesis of a potential antitumor phenanthroindolizidine alkaloid, (-)-antofine, is described. An important feature of this synthesis is the creation of a stereogenic center by using enantioselective catalytic phase transfer alkylation, affording an unnatural alpha-amino acid derivative, together with a ring closing metathesis for pyrrolidine ring construction.     

Enantioselective synthetic method for alpha-alkylserine via phase-transfer catalytic alkylation of 2-phenyl-2-oxazoline-4- carbonylcamphorsultam

[reaction: see text] An enantioselective synthetic method for alpha-alkylserines by the phase-transfer catalytic alkylation of 2-phenyl-2-oxazoline-4-carbonylcamphorsultam (4a) was developed. The phase-transfer catalytic alpha-alkylation of 4a using P2-Et at -78 degrees C gave alpha-alkylation (75 to approximately 99%, 90 to approximately 97% de), which could be easily hydrolyzed to alpha-alkylserines.     

Direct synthesis of methyl 2-diazo-4-aryl-3-butenoates and their application to the enantioselective synthesis of 4-aryl-4-(1-naphthyl)-2-butenoates

An improved one-flask synthesis of various methyl 2-diazo-4-aryl and 4-heteroaryl-3-butenoates, precursors to donor/acceptor substituted carbenoids, is described. Their Rh₂(S-DOSP)₄ catalyzed reaction with 1-acetoxy-3,4-dihydronaphthalene, via a combined C–H activation/Cope rearrangement pathway followed by elimination of acetic acid affords a highly enantioselective (98–99% ee) entry to methyl 4-aryl- and 4-heteroaryl-4-(1-naphthyl)-2-butenoates.     

Solid-phase synthetic method for (±)-α-amino acids via phase-transfer catalytic alkylation

A solid supported glycineimine t-butyl ester was designed and successfully applied to the synthesis of (±)-α-amino acids. The phase-transfer catalytic alkylation, followed by acidic hydrolysis and benzoylation gave N-benzoyl-α-amino acid tert-butyl esters in high yields (up to 92%).     

X-ray Structure of 1- (3' -Phenyl-4' -morpholinyl-2' 5' - dithiole-1' - ylidene)-3, 4-biscarboethoxy-2-thionaphthalene

1INTR0DUCTIONa-Thiocarbonylthioformamideshavebeensynthesizedsince1980[l-23,however,thereisn0reP0rtofthesecomP0undsrelatedtheirpropertiesandreactivities(3).Ac-cordingtothepublishedpapers('-",adithioketone,adithioesterandadithioth-ioesteraresnitablefort4 2JcycloadditionwithalkenicandacetylenicdienophileS.Wewanttoknowwhethera-thiocarbonylthioformamideshavethesamecharacters,thereforethereactionofathiobenzoylthioformmorpholine(1)withdiethylacetylenedicarboxylate(2)wasexplored.Theredultsshowth…     

Highly enantioselective epoxidation of 2-methylnaphthoquinone (vitamin K3) mediated by new cinchona alkaloid phase-transfer catalysts

In the area of catalytic asymmetric epoxidation, the highly enantioselective transformation of cyclic enones and quinones is an extremely challenging target. With the aim to develop new and highly effective phase-transfer catalysts for this purpose, we conducted a systematic structural variation of PTCs based on quinine and quinidine. In the total of 15 new quaternary ammonium PTCs, modifications included, for example, the exchange of the quinine methoxy group for a free hydroxyl or other alkoxy substituents, and the introduction of additional elements of chirality through alkylation of the alkaloid quinuclidine nitrogen atom by chiral electrophiles. For example, the well-established 9- anthracenylmethyl group was exchanged for a "chiral" anthracene in the form of 9-chloromethyl-[(1,8-S;4,5-R)-1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracene. The asymmetric epoxidation of vitamin K(3) was used as the test reaction for our novel PTCs. The readily available PTC 10 (derived from quinine in three convenient and high-yielding steps) proved to be the most enantioselective catalyst for this purpose known to date: At a catalyst loading of only 2.50 mol %, the quinone epoxide was obtained in 76 % yield and with 85 % ee (previously: < or =34 % ee), using commercial bleach (aqueous sodium hypochlorite) as the oxidant. To rationalize the sense of induction effected by our novel phase-transfer catalysts, a computational analysis of steric interactions in the intermediate chlorooxy enolate-PTC ion pair was conducted. Based on this analysis, the sense of induction for all 15 novel PTCs could be consistently explained.     

Enantioselective synthesis of (S)-4-methyleneglutamic acid via tandem conjugate addition-elimination under phase-transfer catalytic conditions

An efficient enantioselective synthetic method for (S)-4-methyleneglutamic acid is reported. Phase-transfer catalytic conjugate addition-elimination of the benzophenone imine of glycine tert-butyl ester in the presence of chiral Cinchona-derived catalysts give the corresponding conjugated addition products (>99% ee), which could be hydrolyzed to chiral (S)-4-methyleneglutamic acid.     

Silica Gel Catalyzed Stereoselective Conversion of Dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-3-(triphenylphosphoranylidene) butanedioates to Dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-2-butenedioates in Solvent-Free Conditions

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, by 1-hydroxy-2-acetonaphthone leads to vinyltriphenylphosphonium salts, which undergo aromatic electrophilic substitution reaction with conjugate base to produce dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-3-(triphenylphosphoranylidene) butanedioates. Silica gel was found to catalyze conversion of dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-3-(triphenylphosphoranylidene) butanedioates to dialkyl 2-(3-acetyl-4-hydroxy-1-naphthyl)-2-butenedioates in solvent-free conditions at 90°;C in fairly good yields.