Exclusive Hiyama‐Type C‐Si Arylation of Unactivated (E)‐β‐Trimethylsilyl Styrenes Catalyzed by Pd Nanoparticles in 1,3‐Dimethyl‐2‐Imidazolidinone (DMI)

ABSTRACT

In contrast to 1,2‐di‐trimethylsilyl styrenes, which in the presence of catalytic amounts of Pd nanoparticles [generated from Pd ₂ dba ₃ /Ag(I)] undergo with aryl iodides a stereoselective C‐H Mizoroki‐Heck arylation pathway, the arylation of monosilylated β‐trimethylsilyl styrenes under the same conditions occurs via a Hiyama‐type C‐Si coupling pathway leading to trans ‐stilbenes. This catalytic system enables the nonactivated in Hiyama‐coupling trimethylsilyl group to react promptly relative to the competing Mizoroki‐Heck pathway. A side product of this process, 1,1′‐diarylethylene, can be completely eliminated using AgBF ₄ as silver salt, and 1,3‐dimethyl‐2‐imidazolidinone (DMI) as an environmentally friendlier solvent over the frequently used in Pd‐catalyzed reactions N , N ‐dimethylformamide or N ‐methyl‐2‐pyrrolidone, in which the current arylation is less chemoselective. The coupling reaction tolerates the presence of boryl substituents in aryl iodide. From the mechanistic point of view, the process involves syn ‐arylpalladation followed by an E2‐type elimination of silyl group and palladium species.