Palladium-catalyzed regioselective C–H alkynylation of indoles with haloalkynes: access to functionalized 7-alkynylindoles

Abstract

A palladium-catalyzed exclusively selective alkynylation of indoles has been reported, affording concise access to 7-alkynylindoles from readily available starting materials.

External oxidant-compatible phosphorus(III)-directed site-selective C–H carbonylation

“…Other transition metals including [Rh(OAc) 2 ] 2 and RhCl 3 showed lower reactivity for this reaction (entries 5 to 6), and the iridium catalyst completely failed (entry 7). The indole 1a′ with the P(V) directing group can undergo Pd-catalyzed C7-selective C–H arylation ( 51 ) and alkynylation ( 52 ) using Ag and Cu salts as the oxidants, which did not provide the corresponding product 3aa′ in the presence of BQ as the oxidant (entry 8). In addition, other P(III) directing groups including N–PCy 2 and N–P i Pr 2 were failed under the standard reaction conditions, because the oxidized by-products generated.…”

Decoding Directing Groups and Their Pivotal Role in C−H Activation

“…[306] Palladium-catalyzed alkynylation of indoles assisted by the phosphinoyl directing group was reported by Wu and co-workers, opening a wide range of further applications of the new alkynylated products (Scheme 63). [308] Organophosphorus compounds have many applications in pharmaceutical and agrochemical fields. Phosphonamides are important precursors for organophosphorus chemistry and as a ligand for metal-complexes.…”

“…Palladium‐catalyzed alkynylation of indoles assisted by the phosphinoyl directing group was reported by Wu and co‐workers, opening a wide range of further applications of the new alkynylated products (Scheme 63). [308] …”

Recent Advances in Metal‐catalyzed Alkylation, Alkenylation and Alkynylation of Indole/indoline Benzenoid Nucleus

“…Wu group reported a Pd‐catalyzed C7‐alkynylation of indole with haloalkynes using a di‐ tert ‐bytylphophinoyl (TBPO) DG (Scheme 45). [46] A Pd(0)‐catalyst and 3‐chloropyridine ligand, along with stoichiometric metal salts Ag 2 CO 3 and Cu(OTf) 2 as the co‐oxidants, are crucial to realize the product formation. In this reaction, a Pd(II) species I is generated in the presence of oxidants.…”