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Asymmetric 1,4-additions of coordinated MeCu.BF3 to chiral enoates: enantioselective syntheses of (S)-(−)-citronellic acid

✍ Scribed by Wolfgang Oppolzer; Robert Moretti; Thierry Godal; Annge Meunier; Heinz Löher

Book ID
104250277
Publisher
Elsevier Science
Year
1983
Tongue
French
Weight
238 KB
Volume
24
Category
Article
ISSN
0040-4039

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✦ Synopsis

nBusP-or cyanide-stabilized RCu.BF3 (R=Me, 4-Me-3-pentenyl) undergo efficient 1,4additions to neopentylether-shielded trans-enoates. Thus chiral B-substituted carboxylic acids e.g. (S)-citronellic acid were obtained in high e.e. (Schemes 2 and 4). Recently greater than 99% enantioselective C-C bond closure 6 to a carboxyl group has been accomplished' by BF3-promoted 1,4-additions of organocopper reagents3 to the crotonate derived from (-)-B-phenylmenthol" (Scheme 1). We ascribed the s-face selectivity of the reactions I+ 2 Scheme I R'Cu.BF,. Et20 9 "-Me 2 R' < 99.3% e.e. to an antiplanar C=C/C=O-disposition in the enoate and thus to a phenyl shielding of its CB-siface. Accordingly, by reversing the order of group introduction, either enantiomer of a B-substituted carboxylic acid should be accessible using the same chiral control element. ' Reported (W.O.) at the 8th International Symposium 'Synthesis in Organic Chemistry',

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