Palladium-Catalyzed Heteroannulation Route to 2-Indolylphosphines

Significance

Presented is a heteroannulation route to 2-indolylphosphine sulfides/oxides by ­reaction of 1-alkynylphosphine sulfides/oxides with 2-iodoanilines under palladium catalysis in yields ranging from low to excellent. The choice of palladium(II) source, solvent, and base was ­significant to the success of the reaction. Among the various conditions tested, the combination of Pd(acac)₂, K₂CO₃, and DMSO gave the best results. For the successful preparation of 2-indol-ylphosphine sulfide, the alkyl substituent (R^²) is crucial. Chloro and bromo groups on the anilines are compatible with the reaction conditions, rendering the products primed for further transformation. The phosphine sulfides/oxides may be reduced to the corresponding trivalent phosphines, one of which was shown to serve as a ligand in a Suzuki cross-couplings.