Synthese von (+)‐(5 S , 6 S )‐Azafrin‐methylester; absolute Konfiguration von Aeginetinsäure and von weiteren vicinalen Apocarotin‐diolen

Synthesis of (+)‐(5 S , 6 S )‐Azafrin Methyl Ester; Absolute Configuration of Aeginetic Acid and of Further Vicinal Apocarotenediols We describe the synthesis of a series of optically active vicinal apo‐β‐carotenediols. Thus, starting from (+)‐(5 S , 6 S )‐5,6‐dihydroxy‐5,6‐dihydro‐β‐ionone ( 2 ) we have prepared the ( Z/E )‐isomeric (+)‐C 15 ‐esters 7 and 8 , the (+)‐retinoic derivatives 14 , 15 , 18 , 19 and (+)‐methyl azafrinate ( 22 ), the enantiomer of the naturally occur‐ring compound (s. Scheme 1 ). Our synthesis also establishes the absolute configura‐tion of aeginetic acid ( 24 ), aeginetoside ( 25 ) and aeginetin ( 26 ), compounds isolated from the root parasite Aeginetia indica by Indian and Japanese workers (s. Scheme 2 ). The presented synthesis of optically active methyl azafrinate confirms our previous assignment [14] of the absolute configuration of azafrin ( 1a ), which was based on degradative evidence.