Anna Iuliano

Addition of diethylzinc to aryl aldehydes catalyzed by (1S,3S)-N,N1-bis[benzyl]-1,3-diphenyl-1,3-propanediamine and its dilithium salt: a mechanistic rationale investigation.

Abstract N,NI-bis-benzyl substituted 1,3-diamine 1a , synthesized in high optical purity, and the corresponding dilithium salt 1b are used, for the first time, as chiral catalysts in the addition of ZnEt2 to aromatic aldehydes. Both 1a and 1b are able to promote the reaction but the products obtained exhibited low enantiomeric excesses. By 1H NMR and UV-CD investigation, experimental evidences about the structure of some reaction intermediates have been gained: reaction pathway consistent with spectroscopic data, chemical and stereochemical results could be postulated.

Application of deoxycholic acid-based copper-phosphite complexes as ligands in the enantioselective conjugate addition of diethylzinc to acyclic enones

Four phosphites obtained by linking enantiomerically pure binaphthylchlorophosphite to the two different hydroxy groups of deoxycholic acid were synthesized and used as chiral ligands in the enantioselective copper-catalyzed 1,4-addition of diethylzinc to acyclic enones. The ligands were screened for activity and enantioselectivity using chalcone as the substrate to establish the influence of the absolute configuration of the binaphthyl moiety as well as the position on the cholestanic backbone of the phosphite moiety. The ligand affording the best results was eventually used in the copper-catalyzed 1,4-addition to various acyclic enones, affording the alkylation products in good yields and e.e.s up to 78%.

ASYMMETRIC ALKYLATION OF AROMATIC ALDEHYDES BY DIETHYL ZINC IN THE PRESENCE OF (S)-N,N,N',N'-TETRAMETHYL-2,2'-DIAMINO-1,1'-BINAPHTHYL

Abstract The new chiral aprotic ligand 1 , N,N,N′,N′-tetramethyl-2,2′-diamino-1,1′-binaphthyl, having C 2 -symmetry structure, affords enantiomeric excesses up to 64% in the asymmetric alkylation of aromatic aldehydes by diethylzinc.

Synthesis of a new family of four deoxycholic acid derived chiral stationary phases and their evaluation in the HPLC resolution of racemic compounds

Abstract Four new chiral selectors obtained by suitable derivatization of the hydroxyl groups of the deoxycholic acid with two identical (homoderivatized) or different (heteroderivatized) arylisocyanates have been prepared and linked covalently to silica gel to obtain new chiral stationary phases (CSPs) for the HPLC separation of enantiomers. The CSPs containing two identical substituents are able to enantiodiscriminate different classes of racemic compounds, or the same racemates to a different extent, a property which depends on the different electronic character of the arylcarbamate moieties. The heteroderivatized CSPs retain the character of the two homoderivatized phases: however, the relative position of the two different arylcarbamate moieties on the deoxycholic backbone strongly affects the enantiodiscrimination capability of these two CSPs.

Chiral phenanthrolines as ligands for Cu(I)-catalyzed asymmetric allylic oxidation

A number of chiral 1,10-phenanthrolines (phens) have been assessed in asymmetric Cu(I)-catalyzed allylic oxidation of cyclohexene. Very effective copper-phen catalysts are obtained only when these ligands bear at least a substituent close to the reactive site of the catalyst. Enantioselectivity up to 36% was obtained.

Synthesis of four cholic acid-based CSPs containing 2-naphthoyl carbamate and 3,5-dinitrophenylcarbamate moieties and their evaluation in the HPLC resolution of racemic compounds

Abstract Four new chiral selectors, obtained by derivatising the hydroxy groups of cholic acid with 2-naphthylisocyanate and 3,5-dinitrophenylisocyanate have been prepared and linked to silica gel to obtain new chiral stationary phases (CSPs) for the HPLC separation of enantiomers. The CSP containing only 2-naphthylcarbamate groups is able to separate the enantiomers of π-acidic substrates, whereas the CSPs containing one 3,5-dinitrophenylcarbamate group and two 2-naphthyl carbamate moieties resolve π-acidic racemic compounds as well as π-basic substrates, with the observed enantiodiscriminating capabilities depending on the arrangement of the different carbamoyl units on the cholestanic backbone.

New 1,3,5-triazine based chiral stationary phase for the high-performance liquid chromatographic separation of enantiomers

2-Chloro-4-(S)-1-(1-naphthyl)ethylamino-6-l-Val-l-valine isopropyl ester 1,3,5-triazine (I), a triazine derivative containing two different chiral moieties, was linked to 3-aminopropylsilanized silica, affording chiral stationary phase (CSP) II, in order to verify its enantiodiscriminating capability and to make a comparison with similar triazine derivative CSPs containing only one kind of chiral moiety. CSP II was successfully employed for the HPLC separation of N-3,5-dinitrobenzoyl amino acid alkylesters and 2,2′-disubstituted-1,1′-binaphthyl compounds. Compound I was also used to prepare a different CSP by in situ derivatization of a prepacked 3-aminopropylsilanized silica column: the obtained CSP exhibited the same characteristics of the CSP prepared by conventional methods.

SYNTHESIS OF DEOXYCHOLIC DERIVED CHIRAL STATIONARY PHASES POSSESSING BOTH ARYLCARBAMATE AND ARYLAMIDE MOIETIES : EVALUATION OF THEIR CHIRAL DISCRIMINATION PROPERTIES IN THE HPLC RESOLUTION OF RACEMIC COMPOUNDS

Abstract Two families of chiral selectors derived from deoxycholic acid, possessing both an arylamide and an arylcarbamate group on the cholestanic backbone were synthesized and covalently bonded to silica gel to afford new chiral stationary phases (CSPs A1 – D1 and A2 – D2 ) for the HPLC resolution of racemic compounds. The chromatographic data concerning the resolution of selected racemic compounds on CSPs A1 – D1 and A2 – D2 were compared with those obtained using analogous CSPs possessing only arylcarbamate groups on the cholestanic system (CSPs A – D ). This has allowed us to establish that the resolution capability of CSPs A1 – D1 and A2 – D2 depends not only on the position of the arylamide group on the cholestanic backbone, but also on the electronic characteristics of the aromatic substituents.

Optically active N-1-phenylethyl derivatives of (1R)-2-amino-1-phenylethanol as chiral auxiliaries in the enantioselective addition of diethylzinc to arylaldehydes

Abstract The aminoalcohols (1R)-2-N[(R)-1-phenylethyl]amino-1-phenylethanol, (1R)-2-N[(S)-1-phenylethyl]amino-1-phenylethanol, and (1R)-2-N-methyl-N[(R)-1-phenylethyl]amino-1-phenylethanol, synthesized by simple procedures, have been used as chiral catalysts in the enantioselective addition of diethylzinc to arylaldehydes, obtaining optically active 1-arylpropanols in good chemical yields (47 to 95%) and e.e.s up to 88%.

The s-triazine moiety as a scaffold for connecting different chiral auxiliaries: synthesis of new biselector CSPs for enantioselective chromatography

An s-triazine scaffold bearing a free and a protected amino group was synthesised and used for connecting two different and differently derivatised aminoacids. Two diastereoisomeric chiral systems were obtained and, once linked to silica gel, they were used in the chromatographic resolution of structurally and electronically different racemic analytes, chosen among the racemates resolved by the isolated aminoacid derivatives. The collected results demonstrate the biselector behaviour of the CSPs in terms of enantiodiscriminating capability towards the class of racemic compounds resolved by both the isolated selectors as well as in terms of the independent action of the two chiral moieties of the system.