Catalytic [2+2+1] Cross‐Cyclotrimerization of Silylacetylenes and Two Alkynyl Esters To Produce Substituted Silylfulvenes

Shibata, Yu; Tanaka, Ken

doi:10.1002/ange.201105517

Cited by 52 publications

(21 citation statements)

References 77 publications

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“…For both substrates, the achiral complex with the more hindered Cp* ligand generally led to a slower reaction than the chiral complex with a 1,2-disubstituted cyclopentadienyl ligand. [18] As expected, cyclometalation was slower at the hindered ortho positions, and with both rhodium catalysts, longer times were required to reach saturation of the deuteration at the 2 position (Figure 2, right graph). Again, the chiral catalyst Rh3 reacted faster.…”

Section: Methodssupporting

confidence: 69%

Chiral Cp‐Rhodium(III)‐Catalyzed Asymmetric Hydroarylations of 1,1‐Disubstituted Alkenes

2013

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Metal-catalyzed functionalizations at the ortho position of a directing group have become an efficient bond-forming strategy. A wide range of transformations that employ Cp*Rh(III) catalysts have been described, but despite their synthetic potential, enantioselective variants that use chiral versions of the Cp* ligand remain scarce (Cp*=pentamethyl cyclopentadienyl). Cyclopentadienyl compounds with an atropchiral biaryl backbone are shown to be suitable ligands for the efficient intramolecular enantioselective hydroarylation of aryl hydroxamates. Dihydrofurans that bear methyl-substituted quaternary stereocenters are thus obtained by CH functionalization under mild conditions.

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Section: Methodssupporting

confidence: 69%

Chiral Cp‐Rhodium(III)‐Catalyzed Asymmetric Hydroarylations of 1,1‐Disubstituted Alkenes

2013

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“…Under carefully optimized conditions, 60 % of anthracene 3 aa is obtained using [(Cp*RhCl 2 ) 2 ] (Cp* = pentamethylcyclopentadienyl) as catalyst and a combination of copper(II) 2ethylhexanoate and decabromo diphenyl ether as oxidants (entry 1). Both the electron-poor complex reported by Tanaka et al [11] and simple RhCl 3 were less efficient (entries 3-4). The employed oxidant combination is essential for the success of the annulation.…”

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confidence: 88%

“…Silver salts were detrimental for the reaction outcome (entries [8][9]. Moreover, both acidic and basic additives decrease the yield significantly (entries [10][11]. The reaction proceeded equally well in cyclohexane and less efficiently in dichloroethane, iPr 2 O, and tBuOH (entries [12][13][14][15].…”

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confidence: 99%

Aromatic Homologation by Non‐Chelate‐Assisted Rh^III‐Catalyzed CH Functionalization of Arenes with Alkynes

2014

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Larger condensed arenes are of interest owing to their electro- and photochemical properties. An efficient synthesis is the catalyzed aromatic annulation of a smaller arene with two alkyne molecules. Besides difunctionalized starting materials, directed C-H functionalization can be used for such aromatic homologation. However, thus far the requirement of either pre-functionalized substrates or suitable directing groups were limiting this approach. Herein, we describe a rhodium(III)-catalyzed method allowing the use of completely unbiased arenes and internal alkynes. The reaction works best with copper(II) 2-ethylhexanoate and decabromodiphenyl ether as the oxidant combination. This aromatic annulation tolerates a variety of functional groups and delivers homologated condensed arenes. Aside from simple benzenes, naphthalenes and higher condensed arenes provide access to highly substituted and highly soluble acenes structures having important electronic and photophysical properties.

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“…Upon elevating the reaction temperature to 150 8C, the yield was improved up to 96 % (entry 2). The reaction proceeded quantitatively in the presence of [{Cp E RhCl 2 } 2 ] (Cp E = 1,3-bis(ethoxycarbonyl)-2,4,5-trimethylcyclopentadienyl), which was recently employed for the oxidative coupling of acetanilides with alkynes [12] as a catalyst in place of [{Cp*RhCl 2 } 2 ], even at 130 8C (entry 3). To our surprise, the reaction was effectively Scheme 1.…”

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confidence: 99%

Synthesis of Fluorene Derivatives through Rhodium‐Catalyzed Dehydrogenative Cyclization

et al. 2012

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Polycyclic aromatic hydrocarbons (PAHs) have attracted considerable attention because of their optical and electronic properties, and their application as p-conjugated functional materials. [1] Fluorene is one of the simplest motifs in PAHs and its derivatives have been employed as important building blocks in a broad range of fields, including light-emitting devices, organic field-effect transistors (OFET), organic photovoltaic cells (OPV), biosensors, etc. [2] Fluorenyl functions have also played important roles in the field of organic synthesis, mainly as unique protecting groups in peptide synthesis. [3] In spite of the simple structures, their construction has been conducted under harsh reaction conditions or through complicated multistep procedures. [4] Meanwhile, transition-metal-catalyzed organic reactions involving CÀH bond cleavage have been significantly developed in recent years as atom-and step-economical tools in precise organic synthesis. [5] Such procedures can provide simple, functional-group-tolerable methods for fluorene synthesis. As shown in Scheme 1, several palladium-catalyzed cyclization reactions of halogenated aromatic substrates were recently reported (routes a-c). [6] Although valuable, the development of a straightforward method involving the cleavage of two CÀH bonds (route d, Scheme 1) [7][8][9] is strongly desired. Herein, we report such a dehydrogenative cyclization. Thus, in the course of our study of rhodium-catalyzed direct oxidative coupling, [10,11] we have found that 1-amino-1,1-diarylalkanes efficiently undergo cyclization to furnish 9H-fluoren-9-amine derivatives without any protection of the amine. Furthermore, related substrates such as 2,2-diphenylalkanoic acids can also be transformed into the corresponding fluorenes through dehydrogenative cyclization and subsequent decarboxylation.In an initial attempt, triphenylmethylamine (1 a) was treated under the standard reaction conditions for our rhodium-catalyzed oxidative coupling. The reaction of 1 a in the presence of [{Cp*RhCl 2 } 2 ] (2 mol % Rh) and Cu-(OAc)·H 2 O (2 equiv) as a catalyst and an oxidant, respectively, in o-xylene at 130 8C for 10 h gave the dehydrogenative cyclization product 9-phenyl-9H-fluoren-9-amine (2 a) in 65 % yield (Table 1, entry 1). Upon elevating the reaction temperature to 150 8C, the yield was improved up to 96 % (entry 2). The reaction proceeded quantitatively in the presence of [{Cp E RhCl 2 } 2 ] (Cp E = 1,3-bis(ethoxycarbonyl)-2,4,5-trimethylcyclopentadienyl), which was recently employed for the oxidative coupling of acetanilides with alkynes [12] as a catalyst in place of [{Cp*RhCl 2 } 2 ], even at 130 8C (entry 3). To our surprise, the reaction was effectively Scheme 1. Synthesis of fluorenes through CÀH bond cleavage. Precedents for a, b, and c. No precedent for d. Table 1: Reaction of triphenylmethylamine (1 a). [a] Entry [Rh] T [8C] t [h] Yield [%] [b]

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Catalytic [2+2+1] Cross‐Cyclotrimerization of Silylacetylenes and Two Alkynyl Esters To Produce Substituted Silylfulvenes

Cited by 52 publications

References 77 publications

Chiral Cp‐Rhodium(III)‐Catalyzed Asymmetric Hydroarylations of 1,1‐Disubstituted Alkenes

Chiral Cp‐Rhodium(III)‐Catalyzed Asymmetric Hydroarylations of 1,1‐Disubstituted Alkenes

Aromatic Homologation by Non‐Chelate‐Assisted Rh^III‐Catalyzed CH Functionalization of Arenes with Alkynes

Synthesis of Fluorene Derivatives through Rhodium‐Catalyzed Dehydrogenative Cyclization

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Catalytic [2+2+1] Cross‐Cyclotrimerization of Silylacetylenes and Two Alkynyl Esters To Produce Substituted Silylfulvenes

Cited by 52 publications

References 77 publications

Chiral Cp‐Rhodium(III)‐Catalyzed Asymmetric Hydroarylations of 1,1‐Disubstituted Alkenes

Chiral Cp‐Rhodium(III)‐Catalyzed Asymmetric Hydroarylations of 1,1‐Disubstituted Alkenes

Aromatic Homologation by Non‐Chelate‐Assisted RhIII‐Catalyzed CH Functionalization of Arenes with Alkynes

Synthesis of Fluorene Derivatives through Rhodium‐Catalyzed Dehydrogenative Cyclization

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Aromatic Homologation by Non‐Chelate‐Assisted Rh^III‐Catalyzed CH Functionalization of Arenes with Alkynes