Asymmetric Synthesis of Dihydrospirotryprostatin B via a Silica Gel‐Mediated Cyclization of Tryptamine‐Ynamide

Comprehensive Summary An asymmetric synthesis of dihydrospirotryprostatin B was achieved in 15 steps (8 purifications) from L ‐tryptophan. The main feature of our synthetic strategy is the efficient construction of spirocyclic oxindole intermediate containing a chiral quaternary carbon center, involving the silica gel‐mediated cyclization of tryptamine‐ynamide and oxidation under neat conditions.