Development of a General Method for the Hiyama–Denmark Cross-Coupling of Tetrasubstituted Vinyl Silanes

General conditions for the Hiyama–Denmark cross-coupling
of tetrasubstituted vinyl silanes and aryl halides are reported. Prior
reports of Hiyama–Denmark reactions of tetrasubstituted vinyl
silanes have required the use of vinyl silanols or silanolates, which
are challenging to handle, or internally activated vinyl silanes,
which lack structural generality. Now, unactivated tetrasubstituted
vinyl silanes, bearing bench-stable tetraorganosilicon centers, and
aryl halides can be coupled. The key to this discovery is the identification
of dimethyl­(5-methylfuryl)­vinylsilanes as bench stable and easily
prepared cross-coupling partners that are readily activated under
mild conditions in Hiyama–Denmark couplings. These palladium-catalyzed
cross-couplings proceed well with aryl chlorides, though aryl bromides
and iodides are also tolerated, and the reactions display high stereospecificity
in the formation of tetrasubstituted alkenes. In addition, only a
mild base (KOSiMe3) and common solvents (THF/DMA) are required,
and importantly, toxic additives (such as 18-crown-6) are not needed.
We also show that these conditions are equally applicable to Hiyama–Denamrk
coupling of trisubstituted vinyl silanes.