SYNTHESIS OF ASPERULOSIDE AGLUCON SILYL ETHER AND GARJASMINE FROM (-GENIPIN VIA GARDENOSIDE AGLUCON BIS(SILYL ETHER) AS A COMMON INTERMEDIATE())

Syntheses of C6-functionalized iridoids represented by asperuloside ag lucon silyl ether (4) and garjasmine were accomplished from (+)-genipi n by utilizing the gardenoside aglucon bis(silyl ether) (3) as a commo n intermediate. During the transformation of 3 into 4, the acid-cataly zed transposition reaction of the tertiary hydroxyl group was found to proceed from more hindered concave side to give C6-hydroxylated compo und having the same stereochemistry as that of C6 in 4. This observed hydroxyl group transposition reaction was interesting since such migra tion of hydroxyl group in the proposed biosynthetic pathway of gardeno side from geniposide proceeded to the opposite direction.