Iron(III) Salt‐Catalyzed Nazarov Cyclization/Michael Addition of Pyrrole Derivatives

Fujiwara, Mai; Kawatsura, Motoi; Hayase, Shuichi; Nanjo, Masato; Itoh, Toshiyuki

doi:10.1002/adsc.200800702

Cited by 73 publications

(39 citation statements)

References 32 publications

(19 reference statements)

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“…14c Another interesting application is a Nazarov cyclization/Michael addition sequence, which has been used to obtain new polyfunctionalized cyclopentenones. 23 …”

Section: Introductionmentioning

confidence: 99%

Understanding the Fate of the Oxyallyl Cation following Nazarov Electrocyclization: Sequential Wagner−Meerwein Migrations and the Synthesis of Spirocyclic Cyclopentenones

2011

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A general reaction sequence is described that involves Nazarov cyclization followed by two sequential Wagner Meerwein migrations, to afford spirocyclic compounds from divinyl ketones in the presence of one equivalent of copper(II) complexes. A detailed investigation of this sequence is described including a study of substrate scope and limitations. It was found that after 4π electrocyclization, two different pathways are available to the oxyallyl cation intermediate: elimination of a proton can give the usual Nazarov cycloadduct, or ring contraction can give an alternative tertiary carbocation. After ring contraction, either [1,2]-hydride or carbon migration can occur, depending upon the substitution pattern of the substrate, to furnish spirocyclic products. The rearrangement pathway is favored over the elimination pathway when catalyst loading was high and the copper(II) counterion is noncoordinating. Several ligands were found to be effective for the reaction. Thus, the reaction sequence can be controlled by judicious choice of reaction conditions to allow selective generation of richly functionalized spirocycles. The three steps of the sequence are stereospecific: electrocyclization followed by two [1,2]-suprafacial Wagner-Meerwein shifts: the ring contraction and then an hydride, alkenyl or aryl shift. The method allows stereospecific installation of adjacent stereocenters or adjacent quaternary centers arrayed around a cyclopentenone ring.

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“…14c Another interesting application is a Nazarov cyclization/Michael addition sequence, which has been used to obtain new polyfunctionalized cyclopentenones. 23 …”

Section: Introductionmentioning

confidence: 99%

Understanding the Fate of the Oxyallyl Cation following Nazarov Electrocyclization: Sequential Wagner−Meerwein Migrations and the Synthesis of Spirocyclic Cyclopentenones

2011

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“…We tested the reaction using various iron salts (FeCl 2 , FeBr 2 , Fe(acac) 2 , Fe(OAc) 2 , Fe(ClO 4 ) 2 ·6H 2 O, Fe(OTf) 2 , FeCl 3 , Fe(ClO 4 ) 3 ·nH 2 O, and Fe(acac) 3 ) and solvents (toluene, tetrahydrofuran (THF), 1,4‐dioxane, acetonitrile, dichloroethane, MeOH, H 2 O, and ionic liquids) using 90 as a model substrate. As anticipated, the desired Nazarov cyclization smoothly proceeded and the cyclized product 91 (R = H) was obtained in over 90% yield using 5 mol% of Fe(ClO 4 ) 3 ·Al 2 O 3 or Fe(BF 4 ) 2 ·6H 2 O as the catalyst (Figure ) 53. An X‐ray crystallographic analysis of the cyclized product 91 revealed the trans relationship between the α‐carbomethoxy group and the β‐phenyl group.…”

Section: Iron‐catalyzed Nazarov Cyclizationmentioning

confidence: 57%

“…The solvent choice was very important in the reaction and CH 2 Cl 2 or the ionic liquid, 1‐butyl‐3‐methylimidazolium bis(trifuluoromethyl)sulfonylamide ([bmim][NTf 2 ]), tributyl(2‐methoxyethyl)phosphonium bis(trifuluoromethyl)sulfonylamide ([P 444ME ][NTf 2 ]), or N,N ‐diethyl, N ‐(2‐methoxyethyl), N ‐methylammonium bis(trifuluoromethyl)sulfonylamide ([N 221ME ][NTf 2 ]) provided excellent results (Figure ) 53. The stereochemistry of the product 91 did not depend on the E/Z ratio of the starting compound 90 , and the Nazarov cyclization product 91 , which had a trans relationship between the α‐carbomethoxy group and the β‐phenyl group, was produced as the major isomer, while a trace amount of the cis isomer was produced in the CH 2 Cl 2 solvent system 53. It was revealed that only the trans ‐ 91 was obtained when the reaction was conducted in the IL solvent 53.…”

Section: Iron‐catalyzed Nazarov Cyclizationmentioning

confidence: 99%

Recent Progress on Nazarov Cyclizations: The Use of Iron Salts as Catalysts in Ionic Liquid Solvent Systems

Itoh

Nokami

Kawatsura

2016

The Chemical Record

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Nazarov cyclization is an important and versatile method for the synthesis of five-membered carbocycles, and extensive studies have been conducted to optimize the reaction. Among recent studies, several trends are recognized. One is the combination of different reactions with Nazarov cyclization in a one-pot reaction system which enables the preparation of unique cyclization products. The second is the use of a transition-metal catalyst, though Lewis or Brønsted acids have generally been used for the reaction. The third is the realization of the asymmetric Nazarov cyclization. The fourth is the base-catalyzed Nazarov cyclization. Furthermore, several useful protocols for realizing Nazarov cyclization have also been developed. The recent progress on Nazarov cyclizations is summarized in Section 2. Section 3 is our chronicle in this field. We focused on the use of iron as the catalyst in Nazarov cyclizations and ionic liquids as solvents: Nazarov cyclization of thiophene derivatives using FeCl3 as the catalyst was accomplished and we succeeded in demonstrating the first example of an iron-catalyzed asymmetric Nazarov reaction. We next established Nazarov cyclization of pyrrole or indole derivatives using Fe(ClO4 )3 ·Al2 O3 as the catalyst with high trans selectivities in excellent yields. Since the cyclized product was reacted with a vinyl ketone in the presence of the same iron salt, the system allowed realization of the sequential type of Nazarov/Michael reaction of pyrrole derivatives. Furthermore, we demonstrated the recyclable use of the iron catalyst and obtained the desired Nazarov/Michael reaction products in good yields for five repetitions of the reactions without any addition of the catalyst using an ionic liquid, [bmim][NTf2 ], as the solvent. We expect that the iron-catalyzed Nazarov cyclization, in particular, in an ionic liquid solvent might become a useful method to synthesize functional molecules that include cycloalkene moieties.

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“…thiophenes [8] or pyrroles [9], and the enantioselective Michael addition of thiols to α, β-unsaturated carbonyl compounds [10].…”

Section: Introductionmentioning

confidence: 99%

Iron‐catalyzed quick homocoupling reaction of aryl or alkynyl Grignard reagents using a phosphonium ionic liquid solvent system

Kude¹,

Hayase²,

Kawatsura³

et al. 2011

Heteroatom Chemistry

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The iron-catalyzed homocoupling reaction of aryl Grignard reagent was completed very quickly when the reaction was carried out in a phosphonium salt ionic liquid solvent system at 0• C for 5 min. Using a similar reaction system, the first example of the iron-catalyzed homocoupling reaction of alkynyl Grignard reagents has also been accomplished using the ionic liquid technology. C 2011 Wiley Periodicals, Inc. Heteroatom Chem 22:397-404, 2011; View this article online at wileyonlinelibrary.com.

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Iron(III) Salt‐Catalyzed Nazarov Cyclization/Michael Addition of Pyrrole Derivatives

Cited by 73 publications

References 32 publications

Understanding the Fate of the Oxyallyl Cation following Nazarov Electrocyclization: Sequential Wagner−Meerwein Migrations and the Synthesis of Spirocyclic Cyclopentenones

Understanding the Fate of the Oxyallyl Cation following Nazarov Electrocyclization: Sequential Wagner−Meerwein Migrations and the Synthesis of Spirocyclic Cyclopentenones

Recent Progress on Nazarov Cyclizations: The Use of Iron Salts as Catalysts in Ionic Liquid Solvent Systems

Iron‐catalyzed quick homocoupling reaction of aryl or alkynyl Grignard reagents using a phosphonium ionic liquid solvent system

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