Synthesis of Polycyclic Indolines by Utilizing a Reduction/Cyclization Cascade Reaction

Subsequent reduction and dearomatizing cyclization reactions open up an entry into the synthesis of novel N-fused polycyclic indolines. The dearomatizing cyclization as key step of the sequence proceeds well with Cu(OTf)(2) or TfOH as catalyst. At elevated temperature reduction of nitro-substituted precursors with iron under acidic conditions affords a broad variety of polycyclic indolines directly in a two-step cascade reaction in good to excellent yields. Using the developed protocol, the alkaloids tryptanthrin and phaitanthrin C have been prepared.

Automated summary

The synthesis of novel N-fused polycyclic indolines was achieved through subsequent reduction and dearomatizing cyclization reactions, resulting in good yields of a broad variety of compounds including alkaloids such as indolines and phaithanthrin C.