We report a palladium-catalyzed,
three-component carbosilylation
reaction of internal symmetrical alkynes, silicon electrophiles, and
primary alkyl zinc iodides. Depending on the choice of ligand, stereoselective
synthesis of either cis- or trans-tetrasubstituted vinyl silanes is possible. We also demonstrate
conditions for the Hiyama cross-coupling of these products to prepare
geometrically defined tetrasubstituted alkenes.
General conditions for the Hiyama−Denmark crosscoupling 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 (KOSiMe 3 ) 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.
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