LIGNANES .11. PREPARATION OF (R)-(+)-BETA-VANYLLYL-GAMMA-BUTYROLACTONE AND ITS USE IN TOTAL SYNTHESIS OF NATURAL LIGNANES

Condensation of vanillin with dimethyl succinate (using LiOMe) gave the ethylenic hemiester 3. Hydrogenation of 3 gave (R,S)-4. The latter was resolved into both its enantiomers by means of (+)-alpha-methylbenzylamine. Ca(BH4)2 reduction of (R)-(+)-4 and (S)-(-)-4 gave the corresponding beta-vanillyl-gamma-butyrolactones (R)-(+)-1 and (S)-(-)-1, respectively. The lactone (R)-(+)-1 was used for the total syntheses of five naturally occurring and optically active lignans such as (-)-anhydrosecoisolariciresinol [16] and (+)-isolariciresinol [20].