Divergent total syntheses of isobatzellines
A/B and batzelline
A were accomplished. A fully substituted common indole intermediate
bearing C-2 methylthio and C-5 chloro groups was constructed via ring
expansion of benzocyclobutenone oxime sulfonate with NaSMe and a benzyne-mediated
cyclization/functionalization sequence as the key steps. The total
synthesis of isobatzelline B was achieved via formation of the iminoquinone
structure by the redox-neutral acid-promoted C-5 proto-dechlorination
of the common indole intermediate. The total syntheses of isobatzelline
A and batzelline A were completed in a divergent manner by oxidation
of the common indole intermediate using MnO2 or Mn(OAc)3, respectively.
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