2002 other bioactive products

other bioactive productsU 1300

02 - 262Synthesis of (+)-Galiellalactone. Absolute Configuration of Galiel-lalactone. — The synthesis of the title compound (XV) is based on thepreformed six-membered ring (II) derived from (R)-(+)-pulegone. Regioselectivereaction of the Grignard reagent, derived from acetal (I) with cyclohexenone(II) and capturing the intermediate enol with trimethylsilyl chloride, providesenol ether (IV). Saturated ketone (VI) is formed as the desired diastereomerby hydrogenation of ketone (V). Acidic treatment over three days of the lattercompound gives bicycle (VII). Palladium-catalyzed carbonylation of enol triflate(IX) in MeOH affords methyl ester (XII). Epoxidation of this ester and finallactone ring formation via hydrolysis of the ester group of major epoxide (XIII)with LiOH followed by acid-catalyzed opening of the epoxide and subsequentlactonization gives the target compound. Synthetic and natural galiellalactonehave opposite optical rotations demonstrating that the natural product is(-)-(XV). — (JOHANSSON, MARTIN; STERNER, OLOV; Org. Lett. 3(2001) 18, 2843-2845; Dep. Org. Bioorg. Chem., Univ. Lund, S-221 00 Lund,Swed.; EN)

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