Currently, catalytically transferable carbenes are limited to electron-deficient and neutral derivatives, and electron-rich carbenes bearing an alkoxy group (i.e., Fischer-type carbenes) cannot be used in catalytic cyclopropanation because of the lack of appropriate carbene precursors. We report herein that acylsilanes can serve as a source of electron-rich carbenes under palladium catalysis, enabling cyclopropanation of a range of alkenes. This reactivity profile is in sharp contrast to that of metal-free siloxycarbenes, which are unreactive toward normal alkenes. The resulting siloxycyclopropanes serve as valuable homoenolate equivalents, allowing rapid access to elaborate β-functionalized ketones.
We have developed a palladium‐catalyzed addition of a C−Si bond of acylsilanes across a range of unactivated allenes. The reaction proceeds with complete regioselectivity, in which a silyl group binds to the central carbon of the allene, allowing for the straightforward access to functionalized alkenylsilane derivatives.
Palladium-catalyzed addition of a C–Si bond in acylsilanes across the triple bonds in an alkyne bearing a carbonyl group at one terminal is reported. The reaction proceeds with excellent regioselectivity,...
We have developed a palladium-catalyzed addition of a CÀ Si bond of acylsilanes across a range of unactivated allenes. The reaction proceeds with complete regioselectivity, in which a silyl group binds to the central carbon of the allene, allowing for the straightforward access to functionalized alkenylsilane derivatives.Organosilicon compounds are essential components in diverse disciplines, encompassing synthetic organic, [1a-c] polymers, materials, [1d,e] bioorganic and medicinal chemistry. [1f,g] The most powerful and most widely used method, both commercially and in the laboratory, for their synthesis involves the transition metal-catalyzed hydrosilylation of unsaturated hydrocarbons, in which a HÀ Si bond is added across alkenes or alkynes. [2] If a CÀ Si bond in organosilanes could be added to unsaturated hydrocarbons in a similar manner, it would be a method of great value since it would allow access to elaborate organosilicon compounds from simpler organosilicon feedstocks with a 100 % atom economy (Figure 1). [3] However, realizing such an insertion reaction into a CÀ Si bond represents a daunting challenge, because, unlike a HÀ Si bond, the requisite oxidative addition of a CÀ Si bond is an uncommon organometallic process. [4] In fact, the cleavage of a CÀ Si bond by transition metal complexes primarily occurs through transmetallation with complexes bearing an X-type ligand, during which a silicon group is eliminated. [1b,c, 5] Therefore, insertion reactions into a CÀ Si bond, except for those using strained silacyclyes (i.e., silacyclopropanes [6] and silacyclobutanes [7] ), silyl cyanides [8] and intramolecular reactions, have not been reported (Figure 1a). [9,10] The Lewis acid-mediated carbosilylation of allylsilanes and related activated silanes have been reported, but, in such reactions, the CÀ Si bond cleavage occurs via a carbocation intermediate. [11] The photochemical addition of a CÀ Si bond of acylsilanes to activated alkynes has been reported, although the applicable alkynes are limited to acetylenedicarboxylates or intramolecular reactions (Figure 1b). [12] We report herein on the palladiumcatalyzed addition of a CÀ Si bond in acylsilanes across allenes, in which a CÀ C double bond can be functionalized with both acyl and silyl groups (Figure 1c). Narasaka and co-workers reported on the palladiumcatalyzed decarbonylative bis-silylation of dimethyl acetylenedicarboxylate using a bis-silyl ketone, which appears to proceed through the oxidative addition of a CÀ Si bond. [13] We also previously reported on the palladium-catalyzed siloxycyclopropanation of alkenes using acylsilanes, in which the oxidative addition of a CÀ Si bond presumably triggers the generation of a key siloxycarbene-palladium
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