摘要：

R)-(+)-3,7-Dimethyloctanoic acid (12b) was synthesized from isovaleraldehyde (5) using a stereospecific five-carbon homologation process. The key transformations involve [3,3] sigmatropic rearrangements of (R)-(+)-(Z)-6-methylhept-2-en-4-ol (10a) and the (S)-(-)-(E) isomer 11a which were prepared from 5 via (±)-6-methylhept-2-yn-4-ol (7a). Under a variety of conditions, Claisen rearrangements of 10a and 11a were shown to proceed with 97-99% chiral transmission, leading, ultimately, to (S)-(+)-(E)-3,7-dimethyl-4-octenoic acid [4b, 94-96% (S)] and 12b. Repetition of this sequence starting from (R)-(+)-3,7-dimethyloctanal (12a) produced ethyl (3S,7R)-3,7,11-trimethyl-4-dodecenoate (6c) in a state of high enantiomeric purity [99% (3S), 96% (7R)]. Ester 6c was converted to 3R, 7R)-3,7,11-trimethyldodecan-1-ol (1d), an important, 15-carbon side chain intermediate in the synthesis of (2R,4′R,8′R)-α-tocopherol (1a).

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