Silylmetalation of Alkenes

Abstract

Silylmetalation of alkenes is challenging due to the low reactivity of the substrates. In contrast, carbometalation of alkenes has been realized through several innovative methods, including activation of the reagent and the substrate. A similar approach could be applicable to silylmetalation of alkenes, and we have recently developed a bimetal activation method using zincate complexes for this purpose. Here, we describe how the silylzincation of alkenes was achieved. First, the strategies for carbometalation of alkenes will be summarized. Secondly, the history and development of silylzincation chemistry are briefly described. Then the details of our findings related to two types of silylzincation of alkenes, as well as recent progress in mechanistic studies, are discussed. The key point in the silylzincation of alkenes proved to be the bimetal activation of the substrate. One metal (copper or titanium) strongly coordinates and activates the alkene moiety, and the other metal (zinc) acts as the electron acceptor from the silyl group by way of the alkene moiety. This dual activation concept is expected to be applicable to other combinations of metals, as well as to new types of reactions.

Rational Design of a Second Generation Catalyst for Preparation of Allylsilanes Using the Silyl-Heck Reaction

“…2−5 This silyl-Heck reaction provides an expedient entry into these important nucleophiles using widely available alkene starting materials. 6 Although our initial conditions provided allylsilanes with good to excellent selectivities for the trans isomers and were functional-group tolerant, the yields of these reactions were moderate (typically ∼60%) due to competitive isomerization of the alkene starting material. 2 …”

In Situ Generation of Silyl Anion Species through Si−B Bond Activation for the Concerted Nucleophilic Aromatic Substitution of Fluoroarenes

“…For example, silylzincates, which are easily prepared from [R 3 SiÀ M] and dialkylzinc, show satisfactory reactivity and good stability. [2][3] However, the preparation and generation of [R 3 SiÀ M] generally involve the use of highly inflammable alkali metals such as Li, Na, and K, with strict requirements for the reaction conditions, [1] such as extremely low temperature. Here, we present a protocol for in situ generation of silyl anion equivalent from readily available, storable, easy-tohandle silylboranes via SiÀ B bond activation [4] with alkoxide anion under mild conditions.…”

Stabile Stammlösungen von Silicium‐Grignard‐Reagenzien: Anwendung in eisen‐ und cobaltkatalysierten radikalischen C(sp3)‐Si‐Kreuzkupplungsreaktionen

“…[10][11][12][13] Fu und Mitarbeiter [10] sowie wir selbst [11,12] hatten kürzlich Lçsungen fürd iese schwierige Umsetzung vorgestellt, die entweder R 3 SiZnCl 3 in einer nickelkatalysierten Kupplung von Alkylbromiden [10] oder R 3 SiBpin 5 in kupferkatalysierten Kupplungen von Alkyliodiden nutzen. [3][4][5]. [3][4][5].…”

“…[1] Ohne einen Arylrest am Siliciumatom kommt die Reaktion auf der Stufe des Disilans zum Erliegen. 3/3' ' [4,5] erfreuen sich noch immer grçßter Beliebtheit in der Synthesechemie.E in anderer Ansatz ist die Überführung von 1 in silicium-und borbasierte Pronukleophile 4 [6] und 5 [7] durch die Reaktion von 1 mit geeigneten Elektrophilen (Schema 1, links). 2/2' ')oder Zink (1 !…”

“…3/3' ')wandelt harte 1 in weiche Siliciumnukleophile um (Schema 1, rechts), und 2/ 2' ' [3] bzw. 3/3' ' [4,5] erfreuen sich noch immer grçßter Beliebtheit in der Synthesechemie.E in anderer Ansatz ist die Überführung von 1 in silicium-und borbasierte Pronukleophile 4 [6] und 5 [7] durch die Reaktion von 1 mit geeigneten Elektrophilen (Schema 1, links). Der weitverbreitete Gebrauch von Si-B-Reagenzien 5 sticht in diesem Zusammenhang klar hervor.…”