β-Carboline Amides as Intrinsic Directing Groups for C(sp²)–H Functionalization

Abstract

Many site-selective palladium-catalyzed C-H functionalization methods require directing groups. We report here β-carboline amides as intrinsic directing groups for C(sp²)-H functionalization. Various substrates including the natural product alangiobussinine and the marinacarboline core structure were functionalized using carboline-directed δ-C(sp²)-H alkynylations. This transformation proceeds under mild conditions and is compatible with a wide variety of β-arylethamines. δ-Alkynylation of β-arylethamines via a six-membered palladacycle is favored over γ-C(sp²)-H bond functionalization when both positions are accessible. The versatility of β-carboline amides as directing groups is evidenced by other δ-C(sp²)-H functionalizations such as alkenylation, arylation, and C-N bond formation.