Totalsynthese von natürlichem α‐Tocopherol. 4. Mitteilung. Aufbau des Chromanringsystems aus Trimethylhydrochinon und einem optisch aktiven C₄‐ bzw. C₅‐Synthon

Abstract

Total Synthesis of Natural α‐Tocopherol Two independent syntheses of ( S )‐6‐hydroxy‐2,5,7,8‐tetramethylchroman‐2‐yl‐methanol ( 8b ), ( Scheme 6 resp. 9 ) as optically active chroman moiety for the preparation of natural vitamin E via ( S )‐6‐acetoxy‐2,5,7,8‐tetramethylchroman‐2‐carboaldehyde ( 2a ) (Scheme 1) and a corresponding side chain are described. Both reaction sequences use trimethyl‐hydroquinone as starting material; one approach employs an optically active C 4 unit ( 10a ) ( Schemes 5 and 6 ) to introduce the required configuration at C(2), the other uses an optically active C 5 ‐synthon ( 11a ) ( Schemes 8 and 9 ) to build the optically active chroman unit. The correct configuration and optical purity of the chroman synthesized is established by correlation with optically pure material of known configuration from which natural vitamin E had already been derived [2].