Fig. 2
Retrosynthetic analysis. The target molecules may be split into the ABCD* (6) and EF (7) fragments, which may be coupled with a Wittig reaction, followed by macrolactonization to complete the synthesis. A direct complex fragment coupling syn-crotylation reaction of 8 with CD* spiroketal aldehyde 9a or 9b was envisioned as the key step in the synthesis of the ABCD* fragment, while a direct complex fragment coupling alkallylation reaction of 10 with aldehyde 11 was envisioned as a critical step in the synthesis of the EF fragment. Crotyl- and allylsilanes 8 and 10 (M = Si) were envisioned to arise from diene 12 and allylchloride 13, greatly simplifying the synthesis. TFA trifluoroacetate, TMSE 2-trimethylsilylethyl, TES triethylsilyl, TBDPS tert-butyldiphenylsilyl, TBS tert-butyldimethylsilyl
