Generation of chromioenamines by reduction of O-acetyloximes with chromium(ii) and their application

Takai, Kazuhiko; Katsura, Noriko; Kunisada, Yuji

doi:10.1039/b105357b

Cited by 23 publications

(19 citation statements)

References 12 publications

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“…Sequential single‐electron reduction with two equivalents of Cu I would convert the oxime 1 into the iminyl radical A and then into the iminylcopper(II) species B . Species B would then tautomerize to generate a copper(II) enamide C . Conjugate addition of C to the unsaturated N ‐Ts imine 2 and subsequent intramolecular cyclization would liberate TsNH 2 and give dihydropyridine intermediate F (see product 3 ra in Table ), which would be oxidized by Cu II to furnish the pyridine product 3 .…”

Section: Methodsmentioning

confidence: 99%

Synthesis of Highly Substituted Pyridines through Copper‐Catalyzed Condensation of Oximes and α,β‐Unsaturated Imines

2017

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A copper‐catalyzed condensation reaction of oxime acetates and α,β‐unsaturated ketimines to give pyridine derivatives is reported. The reaction features mild conditions, high functional‐group compatibility, and high regioselectivity with respect to unsymmetrical oxime acetates, thus allowing the preparation of a wide range of polysubstituted pyridines, many of which are not readily accessible by conventional condensation methods.

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Section: Methodsmentioning

confidence: 99%

Synthesis of Highly Substituted Pyridines through Copper‐Catalyzed Condensation of Oximes and α,β‐Unsaturated Imines

2017

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“…A reasonable reaction path is shown in Scheme 2. Here, the molecular events start with the formation of an N-centered radical [42] which is assumed to be the intermediate of a reductive dehydroxylation. The resulting imine is supposed to give a C-centered radical species [37] [41] [43] which reacts with a second Cr II ion to a s-alkyl -Cr intermediate, which is the key intermediate in the evolution of the configuration (similarly to the case of the C¼O bond reduction).…”

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confidence: 99%

Amino Acid Ligand Chirality for Enantioselective Syntheses

Micskei

Patonay

Caglioti³

et al. 2010

Chemistry & Biodiversity

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Amino acids are attractive sources of chirality in stoichiometric or catalytic transition metal/organic chemistry. In spite of easy availability and other advantages, the application of these ligands is hindered by several problems. Now, at the dawn of emerging D-amino acid biochemistry, efforts in this direction are becoming increasingly important. The results of research on application of amino acid ligands for transition-metal reagents in organic syntheses are reviewed in the present work.

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“…In a simple one-pot procedure, the 2-siloxy-2,3dihydrofuran derivatives can be converted to furans, pyrroles and thiophenes. Although there were previous reports on the synthesis of furans via transition metal-catalyzed coupling of α-diazoketoesters and terminal alkynes, 12 or other available methods, 13,14 the accessibility to pyrroles 15 and thiophenes could make the present reaction a useful synthetic method for five-membered heterocycles. 3,16 3.…”

Section: Discussionmentioning

confidence: 97%

“…This intermediate can then readily undergo dehydrative cyclocondensation to afford the pyrrole product. This method enables expedient synthesis of various functionalized pyrroles that are not readily accessible by previous methods, 12 starting from simple and easily accessible starting materials.…”

Section: Scheme 25 [3+2]-type Cycloaddition Of Enolizable Ketimines With Diazocarbonyl Compoundsmentioning

confidence: 99%

“…Ethyl 2-isopropyl-1-oxo-10b-phenyl-1,5,6,10b-tetrahydropyrrolo[2,1-a]isoquinoline-3-carboxylate (3aba'): Orange oil (50%, eluent = hexane/EtOAc (96:4)); 1 H NMR (400MHz, CDCl3) δ 7.88 (dd, J = 7.6, 1.6 Hz, 1H), 5H), (m, 1H), 7.12-6.91 (m, 2H), 4.47 (q, J = 6.9 Hz, 2H),3.73-3.67 (m, 1H), 3.58-3.43 (m, 1H), 3.02-3.98 (m, 1H), 2.89-2.66 (m, 2H), 1.45 (t, J = 7.1 Hz, 3H), 1.22 (d, J = 10.8, 3H), 1.21 (d, J = 10.8, 3H); 13 C NMR(100 MHz, CDCl3) δ 201.5, 163.1, 162.0, 140.9, 134.3, 133.1, 128.48, 128.45, 128.4, 127.8, 127.7, 127.4, 126.6, 120.1, 73.3, 62.4, 41.6, 29.5, 24.2, 21.21, 21.15,14.2; HRMS (ESI) Calcd for C24H26NO3 [M + H] + 376.1913, found 376.1908. Ethyl 3-methyl-5-phenyl-1H-pyrrole-2-carboxylate (3acb): White solid (35%, eluent = hexane/EtOAc (96:4)); Mp = 114-116 °C; 1 H NMR (400 MHz, CDCl3) δ 9.15 (s, 1HCDCl3) δ 161.8, 135.1, 131.4, 129.4, 129.0, 127.6, 124.6, 119.9, 110.2, 60.1, 14.6, 13.0; HRMS (ESI) Calcd for C14H16NO2 [M + H] + 230.1181, found 230.1183 Ethyl 1,4-bis(4-methoxyphenyl)-3-methyl-1H-pyrrole-2-carboxylate (3adb): Yellow oil (32%, eluent = hexane/EtOAc (98:2)); 1 H NMR (400 MHz, CDCl3) δ 7.34 (d, J = 8.5Hz, 2H), 7.25(d, J = 8.7 Hz, 2H), 4H), 6.89 (s, 1H), 4.18 (q, J = 7.1 Hz, 2H), 3.868 (s, 3H), 3.866 (s, 3H) 2.47 (s, 3H), 1.17 (t, J = 7.1 Hz, 3H); 13 C NMR(100 MHz, CDCl3) δ 161.5, 158.8, 158.3, 134.5, 129.7, 127.5, 127.32, 127.28, 126.8, 125.8, 121.6, 113.9, 113.6, 59.7, 55.5, 55.3, 14.2,12.2; HRMS (ESI) Calcd for C22H24NO4 [M + H] + 366.1705, found 366.1701…”

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confidence: 99%

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Copper-catalyzed condensation reactions for the synthesis of multisubstituted heteroarenes

Tan¹

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Heteroarenes are ubiquitously found in many biologically active natural and manmade products such as pharmaceuticals, polymeric materials, and are also essential building blocks for the synthesis of complex molecules. Thus, the efficient and regioselective synthesis of heteroaromatic compounds has been one of the main topics of interest for organic, medicinal and material chemists. Over the past decades, transition metal catalysts have emerged to be attractive and powerful tools to enable heteroarene synthesis with a broad functional group compatibility and unique reaction patterns, thus complementing the limitations of classical synthetic methods. This thesis describes the development of new copper-catalyzed condensation methods for the synthesis of highly substituted heteroarenes such as pyrroles, furans, thiophenes, and pyridines. Following the general introduction described in Chapter 1, Chapter 2 describes a copper-catalyzed condensation of imines and diazocarbonyl compounds to afford highly substituted pyrroles, which is also applicable to the synthesis of lamellarin family of natural products. Chapter 3 describes an extension of the method developed in Chapter 2, that is, a copper-catalyzed condensation of 2-siloxy-1-alkenes and diazocarbonyl compounds into highly substituted 2-siloxy-2,3-dihydrofurans. The 2siloxy-2,3-dihydrofurans serve as versatile surrogates for the preparation of furans, pyrroles and thiophenes in one-pot. In Chapter 4, we have established a copper-catalyzed condensation of O-acetyl oximes and α,β-unsaturated imines to afford highly substituted pyridines. The reactions developed herein commonly feature simple and low cost catalytic systems, broad functional group tolerance, regioselective formation of highly substituted heteroarenes starting from readily available starting materials. Chapter 1 1 Chapter 1. General Introduction Scheme 1.2. Classical pyridine synthesis Transition metal-catalyzed synthesis of heteroarenesOver the past decades, numerous methods for the synthesis of heterocycles, including the privileged five-and six-membered heteroarenes, via transition metal catalysis have been developed. 6 Transition metal catalysts often exhibit good level of functional group compatibility and unique reaction patterns, and hence can allow access to heterocycles with substitution patterns that are not readily synthesized by classical methods. In this context, copper is one of the most extensively studied transition metals in the development of heterocycle-forming reactions due to its unique redox and coordination ability as well as its relatively low cost and toxicity. 7 Indeed, as examples discussed below illustrate, a number of copper-catalyzed reactions have been developed for the synthesis of highly substituted pyrroles and pyridine, among other heterocycles. In 2007, Buchwald et al. reported on a copper-catalyzed vinylation of 1,2-bis-Boc-hydrazides with vinyl iodides to afford bis-Boc intermediates, which undergo [3,3]rearrangement and cyclization to afford pentasubstituted pyrro...

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Generation of chromioenamines by reduction of O-acetyloximes with chromium(ii) and their application

Abstract: Chromioenamines can be generated by treatment of O-acetyloximes with chromium(II) via two steps of one-electron reduction and successive isomerization, and the species react with aldehydes to give gamma-amino alcohols after reduction with LiAlH4.

Cited by 23 publications

References 12 publications

Synthesis of Highly Substituted Pyridines through Copper‐Catalyzed Condensation of Oximes and α,β‐Unsaturated Imines

Synthesis of Highly Substituted Pyridines through Copper‐Catalyzed Condensation of Oximes and α,β‐Unsaturated Imines

Amino Acid Ligand Chirality for Enantioselective Syntheses

Copper-catalyzed condensation reactions for the synthesis of multisubstituted heteroarenes

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