Catalytic Silylation of Unactivated C–H Bonds

Cheng, Chen; Hartwig, John F.

doi:10.1021/cr5006414

Cited by 609 publications

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“…[1,2] However, the development of enantioselective variants of these reactions, particularly enantioselective functionalization of alkyl C-H bonds, has been limited (Scheme 1). [3][4][5] Kuninobu, Murai and Takai reported the Correspondence to: John F. Hartwig, jhartwig@berkeley.edu.…”

Section: Graphical Abstractmentioning

confidence: 99%

“…[39] The absolute configurations of the stereogenic centers in 7 were unambiguously determined by single-crystal X-ray analysis. (2) In summary, we have developed an enantioselective silylation of cyclopropanes, which constitutes the first highly enantioselective silylation of an alkyl C-H bond and the first catalytic, enantioselective functionalization of the C-H bond in a cyclopropane to form a carbon-heteroatom bond. The silylation process occurs in high yield and enantioselectivity and tolerates a wide range of functional groups when catalyzed by a Rh complex containing a chiral bisphosphine.…”

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Rhodium‐Catalyzed Enantioselective Silylation of Cyclopropyl C−H Bonds

Lee

Hartwig

2016

Angewandte Chemie

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We describe an enantioseleclive silylation of cyclopropanes catalyzed by a rhodium precursor and the bisphosphine (S)-DTBM-SEGPHOS. (Hydrido)silyl ethers, generated in situ by the dehydrogenative silylation of cyclopropylmethanols with diethylsilane, undergo asymmetric, intramolecular silylation of cyclopropyl C-H bonds in high yields with high enantiomeric excesses in the presence of the rhodium catalyst. The resulting enantioenriched oxasilolanes are suitable substrates for Tamao-Fleming oxidation to form cyclopropanols with conservation of the ee from the C-H bond silylation. Preliminary mechanistic data suggest that C-H cleavage is likely to be the turnover-limiting and enantioselectivity-determining step. Graphical Abstract(Hydrido)silyl ethers, generated in situ by the dehydrogenative silylation of cyclopropylmethanols with diethylsilane, undergo asymmetric, intramolecular silylation of cyclopropyl C-H bonds in high yields with high enantiomeric excesses in the presence of a rhodium catalyst. The silylation products are suitable substrates for Tamao-Fleming oxidation to form cyclopropanols with conservation of the ee from the C-H bond silylation.Keywords asymmetric catalysis; C-H activation; cyclopropane; rhodium; silylation The functionalization of C-H bonds with boranes and silanes has been studied intensively, due to the high regioselectivity of these processes for sterically accessible C-H bonds and widespread utility of the products. [1,2] However, the development of enantioselective variants of these reactions, particularly enantioselective functionalization of alkyl C-H bonds, has been limited (Scheme 1). [3][4][5] Kuninobu, Murai and Takai reported the Correspondence to: John F. Hartwig, jhartwig@berkeley.edu. Supporting information for this article is given via a link at the end of the document. HHS Public Access Author ManuscriptAuthor Manuscript Author ManuscriptAuthor Manuscript asymmetric silylation of a C-H bond to generate a stereogenic silicon center with up-to 88% enantiomeric excess (ee) (Scheme 1A). [6,7] Shibata, He, Murai and Takai independently reported the synthesis of planar chiral compounds with moderate to high enantioselectivities by asymmetric C-H silylation of ferrocenes. [8][9][10] Recently, we reported an enantioselective silylation of aryl C-H bonds to form enantioenriched benzoxasilole products with up-to 99% ee. [11] Although these reactions can occur with high enantioselectivity, they are limited to the functionalization of aryl C-H bonds. The only published set of enantioselective silylations of alkyl C-H bonds occurs with low ee (37-40% ee) and with limited scope (Scheme 1B). [12] To create the first silylations of alkyl C-H bonds that occur with high enantioselectivity, we investigated systems for the reactions of cyclopropanes. C-H bonds of cyclopropanes are more reactive than sp 3 C-H bonds of unstrained rings or alkyl chains, [13] and the rigid conformation of a cyclopropane could allow for high stereoselectivity. Yu and co-workers reported enantioselective...

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Rhodium‐Catalyzed Enantioselective Silylation of Cyclopropyl C−H Bonds

Lee

Hartwig

2016

Angewandte Chemie

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“…Then, preliminary DFT calculations were performed in order to evaluate this speculation (see Supporting Information). The transition state for CH bond activation TS [4][5] is the highest point in our computed free energy profile. Based on the energetic span concept, 12 the step from the most stable intermediate 3 to TS 4-5 was predicted to be the rate-limiting state of the catalytic cycle, with an overall barrier of 27.6 kcal mol ¹1 .…”

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“…Numerous catalyst systems have been proposed for utilization in the silylation of the aromatic CH bonds of arenes. 5 For example, the Hartwig group, as well as our own group, have demonstrated that platinum complexes bearing the hydrotris(3,5-dimethylpyrazolyl)borate (Tp Me2 ) ligand showed high catalytic activities in dehydrogenative aromatic CH silylation with hydrosilanes. 6,7 While the intramolecular CH silylation of other substrates has also been investigated, 6 to our knowledge, the platinumcatalyzed dehydrogenative cyclization of 2-(dialkylsilyl)biaryls 1 has not been reported.…”

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Synthesis of Dibenzosiloles via Platinum-catalyzed Intramolecular Dehydrogenative Cyclization of 2-(Dialkylsilyl)biaryls

Murata¹,

Takizawa²,

Sasaki³

et al. 2016

Chem. Lett.

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The intramolecular dehydrogenative cyclization of 2-(dialkylsilyl)biaryls proceeded in the presence of a catalytic amount of platinum(II) chloride and potassium tris(3,5-dimethyl-1-pyrazolyl)borohydride to give good yields of the corresponding dibenzosilole derivatives. Keywords: C-H activation | Platinum catalyst | C-Si bond formationThe interesting properties of silicon-containing cyclic π-electron systems, such as their light-emitting ability, have made them worthwhile targets for synthesis.1 During the past few years, considerable attention has been devoted to the transitionmetal-catalyzed constructions of silicon-containing heterocycles.2,3 Among them, direct CSi bond formation through CH bond activation serves as an attractive atom-economical and environmentally benign strategy. Takai and co-workers reported the rhodium-catalyzed dehydrogenative cyclization of 2-(dialkylsilyl)biaryls 1, affording the corresponding dibenzosiloles 2 (Scheme 1). 4 However, unfortunately, the rhodium catalyst system has some limitations due to competing side reactions, e.g., the reduction of CCl bonds and the activation of benzylic CH bonds. Furthermore, in several cases, the use of a sacrificial hydrogen acceptor was required.On the basis of recent advances in catalytic CH silylation, we assumed that the use of another catalyst system would overcome these limitations and problems. Numerous catalyst systems have been proposed for utilization in the silylation of the aromatic CH bonds of arenes.5 For example, the Hartwig group, as well as our own group, have demonstrated that platinum complexes bearing the hydrotris(3,5-dimethylpyrazolyl)borate (Tp Me2 ) ligand showed high catalytic activities in dehydrogenative aromatic CH silylation with hydrosilanes. 6,7 While the intramolecular CH silylation of other substrates has also been investigated, 6 to our knowledge, the platinumcatalyzed dehydrogenative cyclization of 2-(dialkylsilyl)biaryls 1 has not been reported. Therefore, we decided to investigate the platinum-catalyzed intramolecular CH silylation of 1. In this paper, we wish to report an improved catalyst system for the synthesis of dibenzosilole derivatives 2 from 1.In order to optimize the reaction parameters, we investigated the reaction of 2-(dimethylsilyl)biphenyl (1a). The results are summarized in Table 1. When 1a (0.25 mmol) was treated with catalytic amounts of PtCl 2 and Tp Me2 K (1 mol % each) in THF (0.5 mL) at 140°C for 4 h, an intramolecular cyclization took place to afford 5,5-dimethyldibenzosilole (2a) in 79% yield (Entry 1). An approximately stoichiometric amount of hydrogen (ca. 5.5 mL, 1 atm) was simultaneously produced. Different catalyst precursors were subsequently investigated. Although [IrCl(cod)] 2 showed some catalytic activity (Entry 3), PtO 2 , [RhCl(cod)] 2 , and [RuCl 2 (p-cymene)] 2 were found to be ineffective (Entries 2, 4, and 5). The combination of PtCl 2 and Tp Me2ligand was effective for this cyclization; however, employing TpK (Tp: hydrotris(pyrazolyl)borate) or BpK (Bp: dihydrobis(pyraz...

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“…Thus, we focused on catalytic CH silylation of (hetero)arenes using 1 without directing groups ( Figure 1). 5,6 Herein, we report the synthesis of sp 2 CHOMSi reagents via straightforward silylation with an iridium catalyst.…”

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Straightforward Synthesis of HOMSi Reagents via sp2 C–H Silylation

Minami¹,

Komiyama²,

Hiyama³

2015

Chemistry Letters

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Straightforward C–H silylation of heteroarenes and alkenes was found to provide efficient access to organo-HOMSi reagents as stable silicon reagents for cross-coupling. Various heteroarenes and terminal alkenes were silylated to show the versatility of the reaction. This method was applied in double silylation reactions to give bisHOMSi reagents. The silylation products could be used in the cross-coupling reaction with haloarenes easily.

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Catalytic Silylation of Unactivated C–H Bonds

Cited by 609 publications

References 156 publications

Rhodium‐Catalyzed Enantioselective Silylation of Cyclopropyl C−H Bonds

Rhodium‐Catalyzed Enantioselective Silylation of Cyclopropyl C−H Bonds

Synthesis of Dibenzosiloles via Platinum-catalyzed Intramolecular Dehydrogenative Cyclization of 2-(Dialkylsilyl)biaryls

Straightforward Synthesis of HOMSi Reagents via sp2 C–H Silylation

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