Chirale 2‐Benzopyran‐3‐carbonsäure‐Derivate durch Oxa‐Pictet‐Spengler‐Reaktion von (<i>S</i>)‐3‐Phenylmilchsäure‐Derivaten

Abstract

Chiral 2‐Benzopyran‐3‐carboxylates by Oxa‐Pictet‐Spengler Reaction of ( S )‐3‐Phenyllactic Acid Derivatives Starting with ( S )‐tyrosine, the methyl ( S )‐3‐(3,4‐dihydroxy‐phenyl)lactate ( 15b ) was prepared by acylation, desamination and Dakin oxidation. The phenyl moiety of 15b was sufficiently activated for the reaction with aromatic and aliphatic aldehydes and ketones to yield the alkyl (3 S )‐2‐benzopyran‐3‐carboxylates 16 and 19 . On the other hand, the oxa‐Pictet‐Spengler reaction of the aryl unsubstituted ( S )‐3‐phenyllactic acid ( 6 ) succeeds only with aromatic aldehydes. It was shown that the enantiomeric purity of the compounds 13 , 14 , 15 , 16 and 19 was greater than 96% ee.