C1 Functionalization of β-Carboline via Knochel–Hauser Base-Directed Metalation and Negishi Coupling

The synthesis of C1-functionalized β-carbolines from N-Boc norharman is described. Substitution is realized by employing the Knochel-Hauser base (TMPMgCl·LiCl) followed by transmetalation with ZnCl₂ and subsequent Negishi cross-coupling of the resulting organozinc species. A variety of aryl or heteroaryl bromides participated in this one-pot reaction sequence, allowing for rapid diversification of the β-carboline scaffold in moderate to excellent yields. The reaction protocol has been applied to the synthesis of natural alkaloids nitramarine, nitraridine, eudistomin U, and perlolyrine.