NMR determination of the absolute configuration of β-chiral primary alcohols

β-Chiral primary alcohol was derivatized to an ester by the use of a new axially chiral reagent, 2′-methoxy-1,1′-binaphthalene-8-carboxylic acid (MBCA). The absolute configuration of the original β-chiral primary alcohol was determined by the NOE correlation between the proton signals of the reagent moiety and those of the β-chiral primary alcohol in the ester.     

Synthesis,resolution and absolute configuration of 4-amino-3-phenylpiperidine

Racemic cis-4-amino-1-benzyl-3-phenylpiperidine was prepared by reductive amination of the respective 4-piperidone via its oxime. The resolution of the racemate was accomplished by crystallization as the mandelate. The enantiomeric purity of this material was checked by NMR after derivatization to the corresponding camphorsulfonamide to be 97% ee. The absolute configuration of one enantiomer was confirmed by X-ray single crystal diffraction of the para-bromobenzenesulfonamide derivative.     

Synthesis of eupomatilone-6 and assignment of its absolute configuration

[Reaction: see text]. The Zn-mediated Barbier reaction of the biarylaldehyde 8 with crotyl bromide followed by hydroboration and oxidation provided the gamma-butyrolactones 4 and 5. The stereoselective installation of methyl group at C-3 by using LiHMDS and MeI completed the synthesis of racemic eupomatilone-6 (2) and its diastereomer 3. The spectroscopic data of 2 was in full agreement with reported spectra of natural product, thus confirming the revised relative configuration of eupomatilone-6. Similarly, an optically active (3R,4R,5S)-isomer of eupomatilone-6 (23) was prepared in which the aldol reaction with thiazolidinethione as a chiral auxiliary was employed as a key step. On the basis of the spectroscopic data and optical rotation values of 23, the absolute configuration of eupomatilone-6 was proposed.     

Total synthesis of amphidinolactone A and its absolute configuration

Asymmetric synthesis of amphidinolactone A, a cytotoxic macrolide from the cultured dinoflagellate Amphidinium sp., has been accomplished. Absolute configuration of amphidinolactone A was concluded to be 1 from comparison of the NMR data and [α]_D values of synthetic and natural amphidinolactone A.     

HPLC optical resolution of tricarbonyl(2,3-dihydrotropone)iron and its absolute configuration

Optical resolution of (±)-tricarbonyl(2,3-dihydrotropone)iron was carried out, and the absolute configuration was determined by X-ray diffraction and CD spectroscopic studies.     

A saturated asymmetric isoprene synthon : Synthesis,resolution and absolute configuration

The unknown racemic 3-methyl-4-phenylsulfonylbutanoic acid (4) is synthesized by standard procedures. The acid is resolved into its enantiomers by alternating treatment with l- and d-ephedrine. The S-(+)-acid 4 is converted into R-(+)-dihydrocitronellol (7) in order to determine the absolute configuration and to illustrate its use as a saturated isoprene building block in isoprenoid homologation.     

Synthesis,resolution and absolute configuration of a tolperisone metabolite

1-(4′-Hydroxymethyl-phenyl)-2-methyl-3-(piperidine-1-yl)-propane-1-one M2, a metabolite of tolperisone, was synthesised in a solvent-free Mannich reaction. The optical resolution was carried out by diastereoisomeric salt formation and separation, for which three resolving agents ((2R,3R)-O,O′-dibenzoyl tartaric acid, (2R,3R)-O,O′-di-p-toluoyl tartaric acid and (R)-2-hydroxy-4-(2-methoxyphenyl)-5,5-dimethyl-1,3,2-dioxaphosphorinane-2-oxide (anicyphos)) were found. The absolute configuration of M2 was determined by the single-crystal X-ray diffraction method.     

Enantiomeric resolution and determination of the absolute configuration of dibenzophosphole 5-oxides

The resolution of asymmetrically substituted dibenzophospholes via chromatographic separation of their cyclopalladium derivatives is described for the first time. The absolute configuration of the phosphorus atom was determined by X-ray crystallographic analysis in one case. A general NMR criterion for the complete determination of the configuration of this group of products is proposed. The enantiomeric excess of the resolved compounds was determined by NMR Eu(III) chemical displacement experiments and by HPLC using a chiral stationary phase.     

Synthesis, resolution, and absolute configuration of chiral 4,4'-bipyridines

A chiral polyhalogenated 4,4'-bipyridine derivative is described allowing an easy access to a new family of chiral 4,4'-bipyridines by site-selective cross-coupling reactions. The absolute configurations of all the HPLC separated enantiomers were determined by X-ray diffraction and electronic circular dichroism coupled with time-dependent density functional theory calculations.     

Total synthesis of colombiasin A and determination of its absolute configuration

The total synthesis of the recently reported marine natural product colombiasin A (1) and determination of its absolute configuration are reported. Two Diels-Alder cycloadditions and a palladium-catalyzed rearrangement are employed as key reactions to construct the tetracyclic framework of the target molecule. The enantioselective synthesis of colombiasin A utilizes Mikami's [(S)-BINOL-TiCl2] catalyst to asymmetrically introduce the first chiral center during the initial Diels-Alder reaction and, in conjunction with X-ray crystallographic analysis of a bromine containing derivative, led to the assignment of the absolute configuration of the natural product.     

Synthesis,resolution and absolute configuration of the diol metabolites of precocene I

All four stereoisomers of precocene I 3,4-dihydrodiol have been prepared and their absolute configurations assigned by the exciton chirality method.     

Palladacycle-catalyzed asymmetric hydrophosphination of enones for synthesis of C*- and P*-chiral tertiary phosphines

A highly reactive and stereoselective hydrophosphination of enones catalyzed by palladacycles for the synthesis of C*- and P*-chiral tertiary phosphines has been developed. When Ph(2)PH was employed as the hydrophosphinating reagent, a series of C*-chiral tertiary phosphines were synthesized (C*-P bond formation) in high yields with excellent enantioselectivities, and a single recrystallization provides access to their enantiomerically pure forms. When racemic secondary phosphines rac-R(3)(R(4))PH were utilized, a series of tertiary phosphines containing both C*- and P*-chiral centers were generated (C*-P* bond formation) in high yields with good diastereo- and enantioselectivities. The stereoelectronic factors involved in the catalytic cycle have been revealed.     

Enzymic optical resolution and absolute configuration of tricyclo[5.2.1.02,6]decadienones

Access to optically active endo-tricyclodecadienones 1 (X=CH₂) has been realized by (i) classical resolution of the diastereomeric ephedrine salts of 3 and (ii) pig liver esterase catalyzed kinetic resolution of 2.     

Infrared spectra of the Cl- -C2H4 and Br- -C2H4 anion dimers

Infrared spectra of mass-selected Cl- -C2H4 and Br- -C2H4 complexes are recorded in the vicinity of the ethylene CH stretching vibrations (2700-3300 cm(-1) using vibrational predissociation spectroscopy. Spectra of both complexes exhibit 6 prominent peaks in the CH stretch region. Comparison with calculated frequencies reveal that the 4 higher frequency bands are associated with CH stretching modes of the C2H4 subunit, while the 2 weaker bands are assigned as overtone or combinations bands gaining intensity through interaction with the CH stretches. Ab initio calculations at the MP2/aug-cc-pVDZ level suggest that C2H4 preferentially forms a single linear H-bond with Cl- and Br- although a planar bifurcated configuration lies only slightly higher in energy (by 110 and 16 cm(-1), respectively). One-dimensional potential energy curves describing the in-plane intermolecular bending motion are developed which are used to determine the corresponding vibrational energies and wavefunctions. Experimental and theoretical results suggest that in their ground vibrational state the Cl- -C2H4 and Br- -C2H4 complexes are localized in the single H-bonded configuration, but that with the addition of modest amounts of internal energy, the in-plane bending wavefunction also has significant amplitude in the bifurcated structure.     

Stereospecific co-crystallization of reactant and palladium complex in the resolution of stilbendiamine using N*-chiral ortho-palladated matrix

Resolution of racemic 1,2-diphenyl-1,2-ethanediamine was performed through recrystallization of its diastereomeric adducts 2a,b with N*-chiral ortho-palladated complex (S_CR_N)-1. The structure and absolute configuration of the less soluble (S_CR_N,SS)-2a diastereomer was determined by X-ray diffraction. The complex has an unusual dimeric structure with a palladacycle:diamine ratio of 2:3; the association of 2a with an additional diamine molecule of the same (SS) absolute configuration is achieved due to hydrogen bonds between the coordinated and solvate diamine.     

Synthesis and absolute configuration of annuionone A

Synthesis of both enantiomers of annuionone A (1), an allelopathic agent isolated from Helianthus annuus (sunflower), was accomplished. The absolute configuration of the naturally occurring 1 was determined to be 1S,5R,8R.     

A new acetylenic compound from the rhizomes of Atractylodes chinensis and its absolute configuration

A new acetylenic compound "atractyloyne", (3S,4E,6E,12E)-1-isovaleryloxy-tetradeca-4,6,12-triene-8,10-diyne-3,14-diol (1) was isolated from the rhizomes of Atractylodes chinensis (Compositae) together with a known compound (4E,6E,12E)-3-isovaleryloxy-tetradeca-4,6,12-triene-8,10-diyne-1,14-diol (2). These structures were determined on the basis of the spectroscopic data and chemical evidence, and the absolute configuration of 1 was established by the modified 2-methoxy-2-trifluoromethylphenylacetic acid (MTPA) method.     

Optically active Phosphine oxides : Synthesis and absolute configuration of (menthoxycarbonylmethyl) phenylvinyl phosphine oxide

The enantiomeric(-)(menthoxycarbonlymethyl)phenylvinylphosphine oxide 1b has been prepared and its absolute configuration rigorously established via chemical correlation. One-step decarbalkoxylation of (-)-ethyl(methoxycarbonylmethyl)phenyphosphine oxide 6 was effected with LiCl-H₂O-DMSO and shown to proceed without concomitant racemization at phosphorus.     

Synthesis, optical resolution and absolute configuration of inherently chiral calixarene carboxylic acids

Both enantiomers of inherently chiral calixarene carboxylic acids with ABCD substitution patterns have been prepared by the benzoylation of 25-propoxy-27-(R)-N-(α-phenylethyl)amidomethyloxycalix[4]arene followed by resolution of the diastereomers formed, monobromination of them and removal of the benzoyl and α-phenylethylamide auxiliary groups. The absolute configuration of the calixarenes obtained has been established by X-ray analysis. Preliminary study of the chiral recognition properties of calixarene carboxylic acid was performed.