Rhodium-Catalyzed Synthesis of Silafluorene Derivatives via Cleavage of Silicon−Hydrogen and Carbon−Hydrogen Bonds

Ureshino, Tomonari; Yoshida, Takuya; Kuninobu, Yoichiro; Takai, Kazuhiko

doi:10.1021/ja107698p

Cited by 217 publications

(107 citation statements)

References 36 publications

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“…Under the present conditions, the differences in the yields among the electronic characteristics of the substituent on the aromatic ring of 1 were not particularly large, whereas the reported rhodiumcatalyzed cyclization of 1 with electron-donating groups required an additional hydrogen acceptor. 4 As shown in Table 2, the present reaction was tolerated with fluoro-(Entry 1), chloro-(Entry 2), methyl-(Entries 4 and 5), and methoxy-substituted 1 (Entry 3). Since the undesired reduction of CCl bonds competed under the reported conditions, 4 it is noteworthy that 2c bearing a chlorine atom was provided without loss of the chlorine atom (Entry 2).…”

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confidence: 62%

“…4 As shown in Table 2, the present reaction was tolerated with fluoro-(Entry 1), chloro-(Entry 2), methyl-(Entries 4 and 5), and methoxy-substituted 1 (Entry 3). Since the undesired reduction of CCl bonds competed under the reported conditions, 4 it is noteworthy that 2c bearing a chlorine atom was provided without loss of the chlorine atom (Entry 2). Moreover, unlike the previous report, 4 the intramolecular aromatic CH silylation of 1f bearing a methyl group at the ortho-position of the aromatic ring was also without any complications (Entry 5).…”

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confidence: 62%

“…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.…”

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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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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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“…28 31 π Conjugated molecules containing heteroatom(s), such as sila uorene derivatives, have important uses as organic functional materials such as uorophores, and in solar cell devices. We have reported the synthesis of sila uorene derivatives 28,29 and phospha uorene oxides 30 by intramolecular C H/heteroatom H coupling reactions. Another strategy for the synthesis of heteroatom containing π conjugated molecules is C H/C H coupling reaction of heteroatom bridged biaryl compounds (Scheme 19).…”

Section: H Transformations Leading To the Synthesis Of Organic Funcmentioning

confidence: 99%

The Development of Novel C-H Bond Transformations and Their Application to the Synthesis of Organic Functional Molecules

Kuninobu

2016

J. Synth. Org. Chem. Jpn.

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“…The popular synthetic routes to benzo-and dibenzosiloles involve intra-and intermolecular cyclization reactions with transition metal catalysts [6][7][8][9], and the use of a chiral supporting ligand enables the synthesis of siloles with a chiral silicon center [10,11]. In particular, direct Si-C or C-H activation is a powerful method that does not require an activated functional group on the aromatic ring [12][13][14][15][16][17]. In non-transition metal systems, 2-ethynylphenylsilane derivatives have been cyclized to afford the corresponding benzosiloles using various reactants, such as lithium naphthalenide [18], Lewis acids [19,20] and KH (Equation (1)) [21].…”

Section: Introductionmentioning

confidence: 99%

Intramolecular Chain Hydrosilylation of Alkynylphenylsilanes Using a Silyl Cation as a Chain Carrier

et al. 2016

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Diorganyl[2-(trimethylsilylethynyl)phenyl]silanes 1a-c and methyl-substituted phenylsilanes 1d and 1e were treated with a small amount of trityl tetrakis(pentafluorophenyl)borate (TPFPB) as an initiator in benzene to afford the corresponding benzosiloles (2a-e) in moderate to good yields. However, no reaction was observed for the reaction using [2-(1-hexynyl)phenyl]diisopropylsilane lf. The methyl substituent was tolerated under the reaction conditions and increased the yield of the corresponding benzosilole depending on the substitution position. From the result using 1f, the current reaction was found to require the trimethylsilyl group, which can stabilize intermediary alkenyl carbocations by the β-silyl effect. The current reaction can be considered an intramolecular chain hydrosilylation of alkynylarylsilanes involving silyl cations as chain carriers. Therefore, the silyl cations generated by hydride abstraction from hydrosilanes 1 with the trityl cation causes intramolecular electrophilic addition to the C-C triple bond to form ethenyl cations, which abstract a hydride from 1 to afford benzosiloles 2 with the regeneration of the silyl cations.

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Rhodium-Catalyzed Synthesis of Silafluorene Derivatives via Cleavage of Silicon−Hydrogen and Carbon−Hydrogen Bonds

Cited by 217 publications

References 36 publications

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

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

The Development of Novel C-H Bond Transformations and Their Application to the Synthesis of Organic Functional Molecules

Intramolecular Chain Hydrosilylation of Alkynylphenylsilanes Using a Silyl Cation as a Chain Carrier

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