New entry to the synthesis of clerodane diterpenes. The first enantioselective syntheses of 7-oxo-kolavenic acid and methyl solidagonate.
Kato, M.; Kosugi, H.; Ichiyanagi, T.; Hagiwara, H.; Kodaira, A.; Kusakari, T.; Suzuki, T.; Ando, M.; Lee, J.; Drechsel, P.; Vogler, B.
Tetrahedron (2001), 57(39), 8243-8256

Abstract

Using (1S,5S)-(-)-verbenone (I), readily obtainable from (+)-nopinone, as the chiral source, we have established the general method for prepn. of three kinds of key intermediates, conjugate enones II and III (R=?-H) for the syntheses of neo-trans-clerodanes and III (R=?-H) for those of neo-cis-clerodanes. Starting with the compd. III (R=?-H), the first enantioselective syntheses of (-)-(5R,8S,9S,10R)-7-oxo-cleroda-3,13E-dien-15-oic acid (7-oxo-kolavenic acid) (IV) and solidagonic acid (V) as its Me ester were achieved.