Double Annulative Cascade of Tryptophan-Containing Peptides Triggered by Selectfluor

A common dearomative
strategy toward the kapakahines B/F and chaetominine
natural products is reported. The proposed biomimetic strategy generates
the tetracyclic α-carboline core in a single step, featuring
a selectfluor-mediated dearomatization of preactivated N-Phth-Trp-Xaa-OR dipeptides at the C-terminus. The pivotal
cascade includes a double annulation and the formation of three carbon–heteroatom
bonds while gaining, for the first time, some insight on the diastereoselectivity
outcome during the formation of the α-carboline fragment.