Remarkable Switch of Regioselectivity in Diels–Alder Reaction: Divergent Total Synthesis of Borreverine, Caulindoles, and Flinderoles

Switchable reaction
patterns of dimerization of indole substituted
butadienes via a Lewis acid and thermal activation are reported. While
under acidic conditions dimerization occurred around the internal
double bond of the dienophile, a complete switch of regioselectivity
was observed under thermal conditions, where dimerization occurred
around the terminal double bond of the dienophile. This switch of
regioselectivity was further exploited for the divergent total synthesis
of structurally diverse indole alkaloid natural products.