Pd−C-Induced Catalytic Transfer Hydrogenation with Triethylsilane

Mandal, Pijus K.; McMurray, John S.

doi:10.1021/jo0706123

Cited by 199 publications

(130 citation statements)

References 22 publications

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“…A successful benzyl ester deprotection was achieved in a reaction of triethylsilane and Pd/C (5 %) with in situ formed H-radicals. 30 The deprotection was carried out in methanol-DMF and furnished desired products 3a and 3b in good yields (Scheme 1).…”

Section: Synthesismentioning

confidence: 99%

Photodecarboxylation of N-Adamantyl- and N-Phenylphthalimide Dipeptide Derivatives

Sohora¹,

Ramljak²,

Mlinarić‐Majerski³

et al. 2014

Croat. Chem. Acta

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Abstract. New dipeptide derivatives 1 and 3 were synthesized and their reactivity in the photochemical reaction of decarboxylation was investigated. The photodecarboxylation of N-adamantyl derivatives 1a and 1b and N-phenylphthalimide derivatives 3a and 3b probably takes place from the triplet excited state. The triplet excited state of 1a, 3a and 3b was characterized by laser flash photolysis. N-phenylphthalimides 3a and 3b undergo 2−5 times more efficient photodecarboxylation than N-adamantylphthalimides 1a and 1b. The aminoacid residue (Phe or Gly) at the C-terminus of the dipeptide does not influence the photodecarboxylation efficiency. Product selectivity in the photoreactions is determined by the conformation of the molecules. N-phenylphthalimides with the separated electron donor (carboxylate) and acceptor moiety (phthalimide) give only simple decarboxylation products, whereas N-adamantyl derivatives also give cyclization products.

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Section: Synthesismentioning

confidence: 99%

Photodecarboxylation of N-Adamantyl- and N-Phenylphthalimide Dipeptide Derivatives

Sohora¹,

Ramljak²,

Mlinarić‐Majerski³

et al. 2014

Croat. Chem. Acta

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“…Oxidation of methyl, t-butyl, benzyl, or allyl glycinate with the non-activated manganese oxide(IV) in CH 2 Cl 2 at room temperature for 1 h proceeded efficiently to give desired highly homogeneous imine in high chemical yield (Table 1, entries 2-5). Resulting imino esters 2b-e are substrates of great use for the following asymmetric Mannnich reaction, because such ester functionalities can be generally cleaved without affecting enantiometric purity using acidic reagent, 29) hydrogenation, 30) and Pd-catalyzed reaction, 31) respectively. We next examined the synthesis of imino amides 2f and g, of great value in Petasis reaction, using boric or boronate reagent.…”

Section: Resultsmentioning

confidence: 99%

A Convenient Method for Preparation of α-Imino Carboxylic Acid Derivatives and Application to the Asymmetric Synthesis of Unnatural α-Amino Acid Derivative

Inokuma

Jichu

Nishida

et al. 2017

CHEMICAL & PHARMACEUTICAL BULLETIN

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We describe herein a manganese(IV) oxide-mediated oxidation of N-p-methoxyphenyl (PMP)-protected glycine derivatives for the synthesis of α-imino carboxylic acid derivatives. Using this methodology, utilization of unstable glyoxic acid derivatives was avoided. Furthermore, using this methodology we synthesized novel α-imino carboxylic acid derivatives such as α-imino phenyl ester, perfluoroalkyl etsers, imides, and thioester. The asymmetric Mannich reaction of those novel imine derivatives with 1,3-dicarbonyl compound is also described, and the novel α-imino imide gave improved chemical yield and stereoselectivity compared with those obtained by the use of the conventional α-imino ester-type substrate.Key words α-imino carboxylic acid derivative; heterogeneous oxidant; asymmetric organocatalysis; thiourea; unnatural α-amino acid Unnatural α-amino acids are often seen in varieties of biologically active compounds, 1-4) including pharmaceutics, and have been used as indispensable chiral building blocks for the synthesis of such active compounds.5,6) Additionally, increasing utilities of unnatural amino acids as a key structural element have also been shown in fields of chemical biology and asymmetric transformation.7-11) These contexts evoke much interest of synthetic chemists in asymmetric synthesis of the structural unit.12,13) Enabling easy access to diverse α-amino acids only by changing nucleophiles employed, Mannich-type reaction of α-imino ester has been widely utilized for the asymmetric synthesis.14-20) Generally, condensation of glyoxalates and primary amines affords α-imino esters as the requisite substrate for Mannich-type reaction (Chart 1a); however, the glyoxalates are unstable, and suffer easy hydrolysis or polymerization at room temperature. Additionally, high susceptibility of the resulting α-imino ester to silica gel has forced us to directly use the imino esters for the Mannich reaction without purification, thereby leading to difficulty in maintaining the reaction outcome. In this context, cross-dehydrogenative coupling (CDC) has been investigated for the synthesis of α-functionalized amino acids 21-23) (Chart 1b). The CDC protocol features oxidative preparation of α-imino ester from glycinates with the use of the oxidants such as 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ), CuOAc, Ru(bpy) 3 Cl 2 / light (or N-oxyl radical), or Cu(I)/molecular oxygen, followed by in situ Mannich reaction. Although the CDC protocol is free from the use of unstable glyoxalates, the in situ Mannich reaction has to be performed in the presence of the employed oxidant due to difficulty in achieving complete separation of the imino ester and oxidant, by which the use of the CDC remains within application to the coupling of oxidant-tolerant functional units. Here, we envisioned that the heterogeneous oxidation system enabling facile removal of insoluble oxidants by filtration allowed the imino ester to be readily obtained and subsequently subjected to Mannich reaction under oxidant-free conditions (Chart 1c).

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“…In fact, by employing the conditions described by Mandal and McMurry, amine (R)-11 was isolated in 90% yield after 30 min at rt in the presence of Et 3 SiH and catalytic amount of Pd/C in ethanol. 26 The final step toward (R)-trypargine (1) was the introduction of the guanidine moiety which was carried out with the method described by Bernatowicz and co-workers 4,9 which makes use of 1H-pyrazol-1-carboxyamidine hydrochloride (12) in DMF and diisopropylethylamine. After column chromatography on basic alumina and treatment with methanolic HCl, (R)-trypargine hydrochloride (1 • HCl) was isolated in 77% yield.…”

Section: Resultsmentioning

confidence: 99%

The asymmetric total synthesis of (+)- and (-)-trypargine via Noyori asymmetric transfer hydrogenation

Pilli¹,

Rodrigues²

2009

J. Braz. Chem. Soc.

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Uma síntese total e eficiente da (+) e (-)-tripargina, alcalóide b-carbolínico isolado da pele da rã africana K. Senegalensis, foi realizada em 6 etapas e 38% de rendimento global, a partir da triptamina, tendo como base a construção do sistema b-carbolínico via reação de BischlerNapieralski e a redução enantiosseletiva do intermediário diidro-b-carbolínico via reação de transferência de hidrogênio assimétrica usando o protocolo de Noyori.A concise and efficient total synhesis of (+)-and (-)-trypargine (6 steps and 38% overall yield), a 1-substituted b-carboline guanidine alkaloid isolated from the skin of the African frog K. senegalensis, was developed based on the construction of the b-carboline moiety via BischlerNapieralski reaction and the enantioselective reduction of the dihydro-b-carboline intermediate via an asymmetric transfer hydrogenation reaction using Noyori´s protocol.Keywords: trypargine, tetrahydro b-carboline alkaloid, Bischler-Napieralski reaction, Noyori asymmetric transfer hydrogenation IntroductionThe b-carboline skeleton is widely distributed among natural products including yohimbine (yohimbine and alloyohimbine), corynantheidine (corynantheidine), Rauwolfia (reserpine) and Vinca (vincamine) alkaloids. 1 (-)-Trypargine (1) is a b-carboline alkaloid which has been isolated from the skin of the African racophorid frog, Kassina senegalensis, by Akizawa et al. 2 in 1982 and more recently has also been isolated in nearly racemic form from the methanol extract of the ground ascidian Eudistoma sp. 3 The absolute configuration of natural (-)-trypargine (1) was initially assigned via resolution of its racemate, prepared via the Pictet-Spengler reaction between tryptamine and 4-guanidino butyraldehyde ethyleneacetal, followed by optical rotatory dispersion and circular dichroism studies. 4 Ishikawa and co-workers 4,5 established its absolute configuration by total synthesis via the Pictet-Spengler reaction between (R)-N-benzyl tryptophan methyl ester and 2-ketoglutaric acid, followed by X-ray diffraction analysis of the corresponding methyl ester of the major diastereoisomer. Synthetic (-)-(S)-1-(3´-guanidinopropyl)-1,2,3,4-tetrahydro-bcarboline was shown to be identical to natural (-)-trypargine (1) thus establishing its absolute configuration.The presence of a b-carboline and a guanidine moieties in the structure of (-)-trypargine (1) has led to preliminary evaluation of its biological profile. Neither a full account of the biological properties nor its biosynthetic origin have been reported although one may envision trypargine (1) to be formed from tryptophan and the 2-keto carboxylic acid derived from arginine. It has been reported to be toxic to mice (LD 50 = 16.9 mg kg -1 , intravenous administration) although complete details of this study are lacking. 5,6 Ireland and co-workers 3 have failed to observe significant cytotoxicity in fractions containing trypargine alkaloids against human colon tumor cells. Additionally, (-)-trypargine (1) has been reported to block voltage gated sodium channe...

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Pd−C-Induced Catalytic Transfer Hydrogenation with Triethylsilane

Abstract: In situ generation of molecular hydrogen by addition of triethylsilane to palladium-charcoal catalyst results in rapid and efficient reduction of multiple bonds, azides, imines, and nitro groups, as well as benzyl group and allyl group deprotection under mild, neutral conditions.

Cited by 199 publications

References 22 publications

Photodecarboxylation of N-Adamantyl- and N-Phenylphthalimide Dipeptide Derivatives

Photodecarboxylation of N-Adamantyl- and N-Phenylphthalimide Dipeptide Derivatives

A Convenient Method for Preparation of α-Imino Carboxylic Acid Derivatives and Application to the Asymmetric Synthesis of Unnatural α-Amino Acid Derivative

The asymmetric total synthesis of (+)- and (-)-trypargine via Noyori asymmetric transfer hydrogenation

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