Loganins aglucone 6-acetate

A significant synthetic achievement this year is Fleming s conversion (Scheme 4) of trimethylsilylcyclopentadiene (135) into the racemic aglucone acetate (136) which has already been converted into loganin (Vol. 1, pp. 20, 21 Vol. 4, p. 26). Cycloaddition of (135) to dichloroketen yields the adduct (137), ° whose conversion into the acetate (138) is straightforward the key steps are the clean... 

The missing carbon has been introduced on the compound 6, after MEM protection of the hydroxyl function, upon metallation with with a 1 1 mixture of t-BuOK-LilCA ( compound 7 ). Simple acid work-up afforded the P-methyl acetal of loganin aglucone 8 which is a known intermediate in the synthesis of loganin. 

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