Les β‐cétonitriles groupes protecteurs de la fonction amine. Préparation d'amino‐alcools

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 a multistep procedure to obtain N ‐methylated amino alcohols homologous to natural (−)‐(1 R ,2 S )‐ephedrine.