Ionic Diamine Rhodium Complex Catalyzed Reductive N-Heterocyclization of 2-Nitrovinylarenes

Okuro, Kazumi; Gurnham, Joanna; Alper, Howard

doi:10.1021/jo200320k

Cited by 48 publications

(21 citation statements)

References 48 publications

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“…Note that methyl migration was observed from a dimethyl derivative (R 2 = R 3 = Me in Scheme 8) even for a palladium catalyst, [110] but not when a rhodium catalyst was employed, where a mixture of products was obtained instead. [111] On the other hand, the geometry around the double bond, cis or trans, in the case of disubstituted alkenes does not sensibly affect the reaction, a feature again in common with the triethylphosphite-promoted reaction. [109] Minor differences in the rate of reaction and in the yield of indole have been found when cis or trans 2-nitrostilbene were separately reductively cyclized, as also mentioned in the previous paragraph.…”

Section: Synthesis Of Indolesmentioning

confidence: 97%

“…This is the same preference that had been earlier found when the same cyclization had been conducted employing triethylphosphite as reductant and is probably a general trend. Note that methyl migration was observed from a dimethyl derivative (R 2 =R 3 =Me in Scheme ) even for a palladium catalyst, but not when a rhodium catalyst was employed, where a mixture of products was obtained instead …”

Section: Synthesis Of N‐heterocycles By Intra‐molecular Cyclization Rmentioning

confidence: 99%

“…In recent years, only one report has been published on the use of a transition metal different from palladium for the reductive cyclization of nitrostyrenes by CO. The ionic rhodium complex [Rh(CO) 2 (Me 2 NCH 2 CH 2 NMe 2 )][Rh(CO) 2 Cl 2 ] was employed as catalyst under mild conditions (100 °C, 100 psi, ∼6.8 bar, in THF) . The use of a different rhodium precursor, [Rh(COD)Cl] 2 , either alone or in the presence of different phosphines, was ineffective.…”

Section: Synthesis Of N‐heterocycles By Intra‐molecular Cyclization Rmentioning

confidence: 99%

“…The ionic rhodium complex [Rh(CO) 2 (Me 2 NCH 2 CH 2 NMe 2 )][Rh(CO) 2 Cl 2 ] was employed as catalyst under mild conditions (100°C, 100 psi, 6.8 bar, in THF). [111] The use of a different rhodium precursor, [Rh(COD)Cl] 2 , either alone or in the presence of different phosphines, was ineffective. The reaction worked well even when the substrate contained an aldehydic or keto group bound to the alkene, with no quinoline being formed.…”

Section: Synthesis Of Indolesmentioning

confidence: 99%

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Transition Metal Catalyzed Reductive Cyclization Reactions of Nitroarenes and Nitroalkenes

2019

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Nitroarenes are the entry point for the production of most nitrogen‐containing aromatic compounds. Thus, any transformation that leads directly from them to the final product allows saving one or more synthetic steps. This review deals with homogeneously catalyzed reactions leading to the formation of N‐heterocyclic compounds from nitroarenes or nitroalkenes in one pot. Reactions that lead to the intermediate formation of amines are not considered. Carbon monoxide is the most often employed reductant because it allows selective reactions, is cheap, and only produces CO2 as stoichiometric byproduct. However, the difficulty in handling pressurized CO has stimulated in recent years the development of CO‐surrogates, that is molecules able to liberate CO during the reaction. The use of phosphines and diols has also been developed in conjunction with molybdenum catalysts. The review focusses in more detail on the literature in the period 2006–2018, but reference to earlier work is made when necessary to put recent results in a more general context.

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Section: Synthesis Of Indolesmentioning

confidence: 97%

Section: Synthesis Of N‐heterocycles By Intra‐molecular Cyclization Rmentioning

confidence: 99%

Section: Synthesis Of N‐heterocycles By Intra‐molecular Cyclization Rmentioning

confidence: 99%

Section: Synthesis Of Indolesmentioning

confidence: 99%

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Transition Metal Catalyzed Reductive Cyclization Reactions of Nitroarenes and Nitroalkenes

2019

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“…As a comparison, if the previously investigated protocol based on n ‐butyl formate was applied, lower yields were achieved (see compounds 2 a , 2 h , 2 n , 2 q , and 2 t ), which thus confirmed the effectiveness of phenyl formate as a CO source . Notably, in several cases the achieved yields were higher than those previously reported in the literature by using pressurized CO. For example, the best yields obtained in the cases of compounds 2 a , 2 h , 2 e , and 2 q were 83, 63, 87, and 55 %, respectively. This fact clearly demonstrates that our protocol is a virtuous alternative to those based on the use of pressurized CO.…”

Section: Methodsmentioning

confidence: 98%

Synthesis of N‐Heterocycles by Reductive Cyclization of Nitro Compounds using Formate Esters as Carbon Monoxide Surrogates

2017

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As eries of alkyl and aryl formate esters were evaluated as CO sourcesi nt he Pd-and Pd/Ru-catalyzed reductivec yclization of substituted nitro compounds to afford heterocycles, especially indoles.P henyl formate was found to be the most effective, and it allowed the desired products to be obtained in excellent yields, often highert han those previously reported with pressurized CO. Through detailed experimentsa nd kinetics tudies, we were able to discern between metal-catalyzed and basemediated activation of phenyl formate and confirmed that just the base waseffective in catalyzing its decarbonylation.The catalytic reductivec arbonylation of aromatic nitro compounds is an efficient method for the preparation of al arge variety of bulk [1] and fine [2] chemicals. In particular,d uring the years, ap lethora of nitrogen-containing heterocyclesh ave been prepared from suitably ortho-substituted nitroarenes by using CO as as toichiometricr eductant (Scheme 1) and examples of intermolecularr eactions and of reactions employing bnitrostyrenes and relatedm olecules as reagents are also known. [3] Despite the high efficiency of several of these reactions, their use has not spread outside the limited number of groups that reported them. This is likely mostly due to the fact that they generally involve the use of pressurized CO, which requires safetym easures that are not availablei nm ost synthetic organic laboratories. To overcome this limitation andt o allow more researchers to use this chemistry, several years ago we startedi nvestigating the use of molecules capable of releasing CO in situ, thus avoidingt he need for high-pressure equipmenta nd CO lines. Among several suitabler eagents, [4] we chose to employ formate esters because of their commercial availability,l ow cost, and low toxicity and selected the Pdcatalyzed synthesis of indoles from o-nitrostyrenes (Scheme 1, upper left) as the first reaction to test. We also chose to operate in as ingle glass pressure tube because this equipment is cheap and availablei nd ifferents izes. As teel autoclave can also be used, but without the need forp ressurized CO. Some of the aforementioned CO-releasing reagents require the use of two-chamber reactors to separatet he CO-releasing reaction from the carbonylation one. When we startedt his study,n oa lternative hadb een reported to the use of gaseous CO in nitroarene cyclization reactions. Very recently,Driver and co-workers reportedt he use of Mo(CO) 6 to this aim. [5] However, the toxicity of this CO source is remarkable and could create complications if used on al arger scale.Owing to its very low cost, our initial investigation was devoted to proving if n-butyl formate could be as uccessful CO surrogate in the reductive cyclization of methyl (E)-2-nitrocinnamate (1a).Ru 3 (CO) 12 and [Pd(Phen) 2 ][BF 4 ] 2 (Phen = 1,10-phenanthroline) were chosen as catalysts for preliminary studies. Indeed, Ru 3 (CO) 12 was extensively employed in decarbonylation reactions of alkyl formates, [6] whereas [Pd(Phen) 2 ][BF 4

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Reductive Cyclization of 2‐Nitro‐ and β‐Nitrostyrenes, 2‐Nitrobiphenyls, and 1‐Nitro‐1,3‐Dienes to Indoles, Carbazoles, and Pyrroles

Söderberg

Berkowitz

2022

Organic Reactions

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This chapter presents a comprehensive review of reductive cyclizations of 2‐nitro‐ and β‐nitrostyrenes, 2‐nitrobiphenyls, and 1‐nitro‐1,3‐dienes to furnish indoles, carbazoles, and pyrroles, respectively, as well as heteroatom analogs thereof. Two variations of the reductive cyclization are discussed: the Cadogan–Sundberg reaction, which is mediated by ternary phosphorus compounds, and the Watanabe–Cenini–Söderberg reaction, which employs a palladium catalyst in the presence of carbon monoxide. A few closely related reductive cyclizations are also presented, as are comparisons with other cyclizations that form the nitrogen–carbon bond of indoles and derivatives.

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Ionic Diamine Rhodium Complex Catalyzed Reductive N-Heterocyclization of 2-Nitrovinylarenes

Cited by 48 publications

References 48 publications

Transition Metal Catalyzed Reductive Cyclization Reactions of Nitroarenes and Nitroalkenes

Transition Metal Catalyzed Reductive Cyclization Reactions of Nitroarenes and Nitroalkenes

Synthesis of N‐Heterocycles by Reductive Cyclization of Nitro Compounds using Formate Esters as Carbon Monoxide Surrogates

Reductive Cyclization of 2‐Nitro‐ and β‐Nitrostyrenes, 2‐Nitrobiphenyls, and 1‐Nitro‐1,3‐Dienes to Indoles, Carbazoles, and Pyrroles

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