Direct coupling reactions of alkynylsilanes catalyzed by palladium(II) chloride and a di(2-pyridyl)methylamine-derived palladium(II) chloride complex in water and in NMP

摘要

Symmetrical internal alkynes can be prepared either by diarylation of mono- and bis(trimethylsilyl) acetylene (TMSA and BTMSA) catalyzed by ligand-less palladium(II) chloride or by a di(2-pyridyl)methylamine-derived palladium(II) chloride complex 1 (typical 0.1-1 mol% of Pd loading) in water using pyrrolidine as base and tetra-n-butylammonium bromide as additive. Alternatively, this same process is performed in NMP in the presence of tetra-n-butylammonium acetate (TBAA) as base with even lower Pd loadings (0.001-1 mol% Pd). The same reaction conditions are applied to the synthesis of unsymmetrical internal alkynes by monoarylation of silylated terminal alkynes. Aryl iodides can be coupled with TMSA, BTMSA and silylated terminal alkynes under heating or at room temperature, whereas for aryl bromides couplings are performed under water reflux or at 110 degrees C in the case of NMP. Complex 1 can be reused during several cycles either in water or in NMP without loss of catalytic activity. These simple reaction conditions allow the preparation of internal alkynes without secondary products, most probably by succesive protiodesilylation-Sonogashira coupling.