New entry to the synthesis of clerodane diterpenes. The first enantioselective syntheses of 7-oxo-kolavenic acid and methyl solidagonate

Abstract Using (1 S ,5 S )-(−)-verbenone ( 8b ), readily obtainable from (+)-nopinone ( 3 ), as the chiral source, we have established the general method for preparation of three kinds of key intermediates, conjugate enones 9 and 10 for the syntheses of neo - trans -clerodanes and 11 for those of neo - cis -clerodanes. Starting with the compound 10 , the first enantioselective syntheses of (−)-(5 R ,8 S ,9 S ,10 R )-7-oxo-cleroda-3,13 E -dien-15-oic acid (7-oxo-kolavenic acid) ( 1 ) and solidagonic acid ( 2 ) as its methyl ester ( 48 ) were achieved.