Catalytic enantioselective C–H functionalization of indoles with α-diazopropionates using chiral dirhodium(II) carboxylates: asymmetric synthesis of the (+)-α-methyl-3-indolylacetic acid fragment of acremoauxin A

Goto, Takayuki; Natori, Yoshihiro; Takeda, Koji; Nambu, Hisanori; Hashimoto, Shunichi

doi:10.1016/j.tetasy.2011.05.011

Cited by 61 publications

(19 citation statements)

References 94 publications

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“…[4] Kerr, Davis, Fox, and Hashimoto reported the successful application of Rh-based catalysts for realizing this transformation with diazo compounds. [5] More recently, other catalytic systems have been introduced to enable these reactions. [6] Invariably, however, the scope of these protocols have been limited to the C—H functionalization of indoles in which the N—H group is masked either through alkylation or via a protecting group, [5–6] due to inherently higher reactivity of this functional group toward carbene insertion.…”

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“…[5] More recently, other catalytic systems have been introduced to enable these reactions. [6] Invariably, however, the scope of these protocols have been limited to the C—H functionalization of indoles in which the N—H group is masked either through alkylation or via a protecting group, [5–6] due to inherently higher reactivity of this functional group toward carbene insertion. The application of these catalysts to unprotected indoles have indeed resulted in mixtures of N—H, C—H, and double N—H/C—H insertion products.…”

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“…The application of these catalysts to unprotected indoles have indeed resulted in mixtures of N—H, C—H, and double N—H/C—H insertion products. [5a, 6b, 7] These limitations impose the need of additional protection/deprotection steps for the functionalization of indoles using carbene transfer chemistry ( Scheme 1). …”

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Myoglobin‐Catalyzed C−H Functionalization of Unprotected Indoles

et al. 2018

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Functionalized indoles are recurrent motifs in bioactive natural products and pharmaceuticals. While transition metal-catalyzed carbene transfer has provided an attractive route to afford C3-functionalized indoles, these protocols are viable only in the presence of N-protected indoles, owing to competition from the more facile N-H insertion reaction. Herein, a biocatalytic strategy for enabling the direct C-H functionalization of unprotected indoles is reported. Engineered variants of myoglobin provide efficient biocatalysts for this reaction, which has no precedents in the biological world, enabling the transformation of a broad range of indoles in the presence of ethyl α-diazoacetate to give the corresponding C3-functionalized derivatives in high conversion yields and excellent chemoselectivity. This strategy could be exploited to develop a concise chemoenzymatic route to afford the nonsteroidal anti-inflammatory drug indomethacin.

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Myoglobin‐Catalyzed C−H Functionalization of Unprotected Indoles

et al. 2018

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“…5 Hashimoto and coworkers described the use of dirhodium(II) tetrakis[ N -phthaloyl-( S )-triethylalaninate [Rh 2 ( S -PTTEA) 4 ] to be useful in the C-H functionalization of indoles by α-diazopropionates. 23 Despite a good scope of reactivity, a number of substrate types have thus far proven problematic, including 4-substituted indoles, which have a nucleus prevalent in biologically active natural products. To date, only Hashimoto has achieved the enantioselective C-H functionalization of a 4-substituted indole: the Rh 2 ( S -PTTEA) 4 catalyzed reaction of N -methoxymethyl-4-methylindole with 2,4-dimethyl-3-pentyl-α-diazopropionate in 69% ee.…”

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Rh2(S-PTTL)3TPA—a mixed-ligand dirhodium(ii) catalyst for enantioselective reactions of α-alkyl-α-diazoesters

Boruta¹,

Dmitrenko²,

Yap³

et al. 2012

Chem. Sci.

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Herein we report the synthesis of the mixed ligand paddlewheel complex dirhodium(II) tris[N-phthaloyl-(S)-tert-leucinate] triphenylacetate, Rh2(S-PTTL)3TPA, the structure of which bears similarity to the chiral crown complex Rh2(S-PTTL)4. Rh2(S-PTTL)3TPA engages substrate classes (aliphatic alkynes, silylacetylenes, α-olefins) that are especially challenging in intermolecular reactions of α-alkyl-α-diazoesters, and catalyzes enantioselective cyclopropanation, cyclopropenation, and indole C-H functionalization with yields and enantioselectivities that are comparable or superior to Rh2(S-PTTL)4. Mixing ligands on paddlewheel complexes offers a versatile handle for diversifying catalyst structure and reactivity. The results described herein illustrate how mixed ligand catalysts can create new opportunities for the optimization of catalytic asymmetric processes.

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“…The reactions of indoles with electrophilic metal-bound carbenes, or carbenoids, generated from diazo compounds, takes place under mild reaction conditions. The reaction has been studied for the three principle classes of carbenoids: acceptor-acceptor [9–11], mono-acceptor [12] and donor-acceptor [13–16], and all the carbenoids react preferentially at the electron rich C2–C3 double bond. The catalysts used for the generation of the carbenoids are typically salts of Cu [9,11,13], Rh [10,12,16], Fe [14] and Ru [15].…”

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confidence: 99%