Emanuela Volpini

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.

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’.

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.

Synthesis of enantiopure 2-aminoalkylphenols by stereoselective addition of Grignard reagents to chiral 2-imidoylphenols

Abstract The stereoselective addition of Grignard reagents to chiral 2-imidoylphenols affords enantiopure 2-aminoalkylphenols, a class of ligands useful in stereoselective synthesis. Unusually benzyl- and allyl-magnesium chlorides add to ketimines derived from enolizable o -acylphenols with high yields and stereoselectivities. In this way a stereogenic quaternary C-1 carbon atom is introduced, which could not be obtained by other methods available till now. The mechanism and the asymmetric induction have been explained in agreement with previously obtained results.

Reduction of 4H-chromen-4-ylidene amines: synthesis of 2-[(1-aminoalkyl)-3-aryl-2-propenyl] phenols

Abstract A procedure for the reduction of 4 H -chromen-4-ylidene amines 1 is described, which affords to 2-[(1-aminoalkyl)-3-aryl-2-propenyl] phenols 2 , previously unknown in literature. The efficacy of the procedure is compared with alternative synthetic routes.