Proof of the Absolute Configuration of (−)-(S)-2-Hydroxy-β-ionone by correlation with ursolic acid and with (−)-trans-verbenol

(?)-(S)-2-Hydroxy-β-ionone ( 33 ), (+)-(2 S, 6 S)-2-hydroxy-α-ionone ( 34 ), and their acetates 35 and 36 have been synthesized from (+)-(S)-6-methylbicyclo 4.3.0]-non-1-ene-3, 7-dione ( 3 ). The key intermediate (+)-(1 R, 3 S, 6 S)-2, 2, 6-trimethyl-7-oxobicyclo 4.3.0]non-3-yl acetate ( 7 ) was correlated with a degradation product of the pentacyclic triterpene ursolic acid ( 16 ). Compound 33 was also synthesized by an alternative route starting from (?)-trans-verbenol ( 42 ).