9. Les β-cetonitriles groupes protecteurs de la fonction amine. Preparation d'amino-alcools

Article abstract of DOI:10.1002/hlca.19950780111

β-Ketonitrile-Derived Protecting Groups of the Amino Function.Synthesis of Amino Alcohols.The amino group of natural L-amino acid esters is protected by condensation with 2-oxocyclopentanenitrile (1) or 2-formyl-2-phenylacetonitrile (10).Only the ester group of the formed cyanoenamino esters 2 and 11 reacts with nucleophilic reagents such as organometallics (RMgX, RLi), borohydrides, or metal amides, whereas the cyanoenamino group is unchanged (Schemes 1 and 2).Cyanoenamino alcohols obtained by reduction of cyanoenamino esters 2 are hydrolyzed under acidic conditions to amino alcohols with retention of the configuration of the starting amino acid.This sequence of reactions allows to prepare derivatives of L-tyrosinol from (-)-L-tyrosine (see, e.g., Scheme 4).Cyanoenamino esters 11 are readily methylated at the N-atom to give N-methylated cyanoenamino esters (Scheme 3).This property is exploited on the way of multistep procedure to obtain N-methylated amino alcohols homologous to natural (-)-(1R,2S)-ephedrine.