Cristina Cimarelli

A practical stereoselective synthesis of secondary and tertiary aminonaphthols: chiral ligands for enantioselective catalysts in the addition of diethylzinc to benzaldehyde

A practical procedure for the stereoselective synthesis of a wide group of functionalized aminoalkylnaphthols, using inexpensive starting materials, is reported. Selective N-alkylation was carried out by cyclization of secondary aminoalkylnaphthols with formaldehyde, followed by reduction or alkylation with organometallic reagents. The catalytic activity of this class of compounds was tested in the addition of diethylzinc to benzaldehyde, resulting in moderate to good enantioselectivities. It is noteworthy that the aminonaphthols obtained as the major diastereomer in the solvent free synthesis, have the best asymmetric induction properties in the alkylation reaction.

Application of a new chiral stationary phase containing the glycopeptide antibiotic A-40,926 in the direct chromatographic resolution of β-amino acids

Abstract A new enantioselective HPLC procedure for the direct resolution of β-amino acids is described, based on the use of a new chiral stationary phase (CSP) containing the macrocyclic glycopeptide antibiotic A-40,926, structurally related to teicoplanin, covalently bonded to silica gel microparticles. The new CSP shows higher enantioselectivity and broader applicability in this field compared to the parent teicoplanin phase. The potential for semi-preparative separations on the A-40,926-CSP is demonstrated for a selected cyclic β-amino acid.

Ready N-alkylation of enantiopure aminophenols: synthesis of tertiary aminophenols

Abstract A regioselective indirect alkylation of aminophenols to enantiopure tertiary aminophenols, which are useful chiral ligands for metal-catalysed asymmetric reactions, is reported. This very simple synthetic methodology, through reduction or alkylation of an intermediate benzoxazine, was performed in mild conditions, suitable for the conservation of the configuration of the stereogenic centres. Some crystalline aminophenols show the phenomenon of ‘crystallization-induced asymmetric transformation’.

Asymmetric reduction of enantiopure imines with zinc borohydride: stereoselective synthesis of chiral amines

Abstract The first application of zinc borohydride in the reduction of enantiopure imines for the stereoselective preparation of both the enantiomers of secondary amines is described. A possible explanation of the stereoselectivity and of the reaction mechanism is suggested on the basis of theoretical calculations.

A versatile route to β-enamino esters by acylation of lithium enamines with diethyl carbonate or benzyl chloroformate

Abstract A versatile route to β-enamino esters 1, using accessible starting materials, was developed. Lithiated enamines are allowed to react with diethyl carbonate or benzyl chloroformate with the formation of the β-enamino esters 1a or 1b. The reaction is rather general from a wide array of ketimines and aldimines. Products included cyclic β-enamino esters 1aa-ac, very useful for the synthesis of natural products.

Fast, mild, eco-friendly synthesis of polyfunctionalized pyrroles from β-nitroacrylates and β-enaminones

The reaction of β-nitroacrylates with β-enaminones, at room temperature and under solvent- and promoter-free conditions, affords the one-pot synthesis of polyfunctionalized pyrroles in high yields.

Diastereo and enantioselective entry to β-amino esters by hydride reduction of homochiral β-enamino esters.

Abstract The reduction of homochiral β-enamino esters 1 with sodium triacetoxyborohydride, which occurs with good diastereo- and enandoselectivity in the β-amino esters 2, is described. This procedure allows a straightforward preparation of compounds with known biological activity.

Convenient procedure for the reduction of β-enamino ketones: synthesis of γ-amino alcohols and tetrahydro-1,3-oxazines

γ-Amino alcohols 3 can be easily synthesized in very good yields by reduction of enaminones 1 with Na in Pr1OH–tetrahydrofuran. The reaction is fast, easy to perform, inexpensive and the easily accessible starting materials provide a convenient entry to γ-amino alcohols. The relative configuration assignment of the diastereoisomeric γ-amino alcohols obtained has been established by 1H and 13C NMR studies and unequivocally assigned by their cyclic tetrahydro-1,3-oxazine derivatives 4.

Alkylation of dianions derived from 2-(1-iminoalkyl) phenols: Synthesis of functionalized 2-acyl phenols

Abstract A method has been developed for the almost exclusive C-alkylation of the 2-(1-iminoalkyl) phenols 1 , important organic compounds with a range of employment, which allows the preparation of complex derivatives 4 with good yields starting from easily available materials. The operational simplicity of this method take advantages in providing a variety of alkylated 2-acyl phenols 5 by an easy hydrolysis of the 2-(1-iminoalkyl) phenols 4 . Download full-size image

AN IMPROVED SYNTHESIS OF ENANTIOPURE β-AMINO ACIDS

An improved method for the preparation of both the enantiopure β-amino acids is presented. The diastereomer benzyl β-amino esters, obtained by stereoselective reduction of β-enamino esters, were separated and hydrogenolyzed to the free enantiopure β-amino acids.