TOTAL SYNTHESIS OF NATURAL ALPHA-TOCOPHEROL .4. PREPARATION OF CHROMANE RING-SYSTEM FROM TRIMETHYLHYDROQUINONE AND OPTICALLY-ACTIVE C-4 AND C5 SYNTHONE

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 C4 unit (10a) (Schemes 5 and 6) to introduce the required configuration at C(2), the other uses an optically active C5‐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]. Copyright © 1979 Verlag GmbH & Co. KGaA, Weinheim