Loganin aglucone

A loganin aglucon synthesis has been developed as shown in Eq. 127 245>. Here the key step is the regioselective [3+2]-cycloaddition of 2-cyclopentenone and 3-[(tri-methylsilyl)methyl]-3-buten-2-ylmethylcarbonate. 

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. 

Scheme 13). These [3 + 2] cycloaddition reactions have been applied to the synthesis of natural products, ( )-hirsutene,f " ( )-albene, ( )-brefeldin,f loganin aglucon, and pentalenene3 In earUer applications, reactions with cycloalkenes were employed to construct bicychc compounds (Scheme 14)3 Then, tran -alkenes having a stereogenic center derived from mannitol were employed to control the stereochemistry of the cycloaddition (Scheme 15). ... 

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... 

---