Organocatalytic stereodivergent synthesis of β,β-disubstituted-α-aminoacids

Martinelli, Ada (2017) Organocatalytic stereodivergent synthesis of β,β-disubstituted-α-aminoacids. [Laurea magistrale], Università di Bologna, Corso di Studio in Chimica industriale [LM-DM270], Documento ad accesso riservato.
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Abstract

In this work, we present an organocatalytic stereodivergent synthesis of β,β-disubstituted-α-aminoacids using arylidene azlactones as starting materials. The developed two step synthesis involves a sequential catalysis approach, in which two different catalysts act sequentially to control the absolute configuration of two different stereocenters. With an accurate selection of the catalysts absolute configuration it is possible to obtain all the stereoisomers of the product. The first synthetic step is a catalytic asymmetric transfer hydrogenation of the azlactone C=C double bond. A Jacobsen type thiourea and a Hantzsch ester were chosen as chiral catalyst and hydride donor, respectively. Different azlactones, Hantzsch esters and thioureas were synthetized and tested in the asymmetric transfer hydrogenation to achieve the best stereoselectivity. The second step involves a dynamic kinetic resolution on the reduced azlactone, through a nucleophilic addition to the carbonyl moiety promoted by a bifunctional chiral catalyst. A wide range of nucleophiles and organocatalysts were tested; the best results were reached with alcohols as nucleophiles and squaramide-based cinchona alkaloids as a chiral catalysts. With the optimized conditions two stereodivergent syntheses were then performed, enabling the selective obtainment of both diastereoisomeric product with high enantioselectivities.

Abstract
Tipologia del documento
Tesi di laurea (Laurea magistrale)
Autore della tesi
Martinelli, Ada
Relatore della tesi
Correlatore della tesi
Scuola
Corso di studio
Ordinamento Cds
DM270
Parole chiave
organocatalysis β-disubstituted-α-aminoacids dynamic kinetic resolution stereodivergent synthesis
Data di discussione della Tesi
18 Luglio 2017
URI

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