An environmentally friendly protocol for oxidative halocyclization of tryptamine and tryptophol derivatives

An environmentally friendly and efficient protocol (KX/oxone) for oxidative halocyclization of tryptamine/tryptophol derivatives was developed and demonstrated with 28 examples and concise total synthesis of cyclotryptamine alkaloid protubonines A and B. The distinct advantage of this protocol over all previous methods is that no organic byproduct is generated from a halogenating agent or oxidant, thus greatly reducing the environmental impact of halocyclization and facilitating the post-reaction purification.