Gianni Palmieri

The reaction of vinyl grignard reagents with 2-substituted nitroarenes: A new approach to the synthesis of 7-substituted indoles

Abstract The reaction of three moles of vinylmagnesium bromide with one mole of nitroarene leads to the formation of indoles after aqueous work up of the mixture. Good yields are obtained with ortho -substituted nitroarenes.

A practical o-hydroxybenzylamines promoted enantioselective addition of dialkylzincs to aldehydes with asymmetric amplification

Abstract The addition of dialkylzincs to aldehydes is accelerated considerably by the presence of a catalytic amount of o -hydroxybenzylamine ( R , R )- 2e to give, after hydrolysis, the corresponding alcohol ( S )- 9 in good enantiomeric purity. The origins of the enantioselection have been elucidated. A strong positive nonlinear relationship was observed for the reaction enantioselctivity with the use of o -hydroxybenzylamine 2e , which is very accessible through a short stereoselective synthetic route. The enantiomeric purity of the product 9 is much higher than the d.e. of the chiral source 2e , and the rate of the enantioselective catalysis increases considerably with the increase of the d.e. of ( R , R )- 2e .

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’.

Synthesis of Enantiopure o-Hydroxybenzylamines by Stereoselective Reduction of 2-Imidoylphenols: Application in the Catalytic Enantioselective Addition of Diethylzinc to Aldehydes

Enantiopure o-hydroxybenzylamines 2a–i were synthesized by diastereoselective reduction of the 2-imidoylphenols (R)-1a–i. Conformational analysis enabled the assignment of the absolute configurations of compounds 2a–i. The accessible o-hydroxybenzylamine (R,R)-2h serves as an effective catalyst precursor for highly enantioselective addition of diethylzinc to aliphatic and aromatic aldehydes. This pathway represents a practical and operationally very simple methodology for the enantioselective synthesis of both the enantiomers of secondary alcohols 7a–f.

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.

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.

Gold(III) catalyzed oxidation of sulfides to sulfoxides by nitric acid under phase-transfer conditions: a new synthesis of sulfoxides

Abstract Gold(III) halides catalyze the oxidation of sulfides to sulfoxides in a phase-transfer process. The organic sulfides, dissolved in nitromethane, are treated with (Bu4N+AuCl4−) in catalytic amount and aqueous nitric acid which acts as oxidant. The oxidation of the thio-group is selective and can be carried out also in the presence of other oxidizable groups, such as vinyl, tertiary amino, hydroxy, diol etc, which are left unchanged. Moreover in the case of asymmetric disulfides the reaction is regiospecific leading to the formation of a single monosulfoxide.