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Syntheses of (2 R , 4′ R , 8′ R )‐α‐Tocopherol and (2 R , 3′ E , 7′ E )‐α‐Tocotrienol
Author(s) -
Scott John W.,
Bizzarro Fred T.,
Parrish David R.,
Saucy Gabriel
Publication year - 1976
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19760590135
Subject(s) - chemistry , claisen rearrangement , hydroquinone , tocotrienol , stereoselectivity , stereochemistry , tocopherol , acetic acid , acetal , vitamin e , enantiomer , diketene , ketone , organic chemistry , antioxidant , catalysis
Reaction of trimethyl‐hydroquinone with methyl vinyl ketone in acidic methanol gave rac. ‐2‐methoxy‐2,5,7,8‐tetramethyl‐chroman‐6‐ol ( 8 ). This acetal was converted in four steps to rac. ‐(6‐hydroxy‐2,5,7,8‐tetramethyl‐chroman‐2‐yl)acetic acid ( 13 ). Acid 13 was readily resolved with α‐methyl‐benzylamine to give the ( S )‐enantiomer 14 . Treatment of the unwanted (2 R )‐isomer with acid regenerated 13 , thus leading to an efficient use of this compound. Employing a side chain derived from phytol, 14 was converted to (2 R , 4′ R , 8′ R )‐α‐tocopherol ( 1d , ‘natural’ vitamin E). A reaction sequence from 14 involving two highly stereoselective Claisen rearrangements has provided the first total synthesis of (2 R ,' E ,7′ E )‐α‐tocotrienol ( 2d ).