Tan et al. [78] have also applied an intramolecular epoxide ring-opening in their
synthesis of acortatarin B (Scheme 70).
Epoxidation of glycal 134 with DMDO followed by in situ reduction of the
pyrrole aldehyde and subsequent attack on the epoxide afforded the spiroacetal core
of acortatarin B in high yield as a single diastereomer. Cleavage of the TIPS-ethers
with TBAF then afforded the natural product 38 in excellent yield.
2.11 Cycloaddition Approaches Toward Spiroacetals
Several different cycloaddition strategies have been employed in the synthesis
of spiroacetals, including [4+2]-, [3+2]-, [2+2+2]- [145–147]-, and [2+2+1]cycloadditions [148, 149] (Scheme 71).
Scheme 69 Intramolecular epoxide ring-opening approaches toward papulacandin-like
spiroacetals [142–144]
Scheme 70 Tan et al.’s intramolecular epoxide ring-opening approach toward acortatarin B [78]
238
M.A. Brimble and L.A. Stubbing