Preparation of 2‐aminobenzophenones and polysubstituted quinolines through SmI<sub>2</sub> promoted reductive cleavage of 3‐aryl‐2,1‐benzisoxazoles

Fan, Xuesen; Zhang, Xinying; Zhang, Yongmin

doi:10.1002/hc.20164

Cited by 9 publications

(2 citation statements)

References 30 publications

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“…The data were in agreement with those reported in the literature. 32 4-(4-Methoxyphenyl)-6-methyl-2-phenylquinoline (5j). Following the general procedure, a J.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Mechanistic Insights into the B(C₆F₅)₃-Initiated Aldehyde–Aniline–Alkyne Reaction To Form Substituted Quinolines

Fasano¹,

Radcliffe

Ingleson

2017

Organometallics

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A substoichiometric quantity of the Lewis acid B(C 6 F 5 ) 3 is sufficient to initiate the aldehyde−amine−alkyne reaction, in a one-pot methodology that enables the synthesis of a range of functionalized quinolines. Optimization studies revealed that key requirements for the high-yielding tricomponent reaction initiated by B(C 6 F 5 ) 3 at raised temperatures include an excess of the in situ generated imine (which acts as a hydrogen acceptor) and an alkyne substituent able to stabilize positive charge buildup during the cyclization. Mechanistic experiments revealed that under these conditions B(C 6 F 5 ) 3 is acting as a Lewis acid-assisted Brønsted acid, with H 2 O−B(C 6 F 5 ) 3 being the key species enabling catalytic quinoline formation. This was indicated by deuterium labeling studies and the observation that the cyclization of N-(3-phenylpropargyl)aniline using B(C 6 F 5 ) 3 under anhydrous conditions afforded the zwitterion [(N-H-3-B(C 6 F 5 ) 3 -4-Ph-quinolinium], which does not undergo protodeboronation to release B(C 6 F 5 ) 3 and the quinoline product under a range of conditions. Finally, a brief substrate scope exploration demonstrated that this is an operationally simple and effective methodology for the production of functionalized quinolines.

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“…The data were in agreement with those reported in the literature. 32 4-(4-Methoxyphenyl)-6-methyl-2-phenylquinoline (5j). Following the general procedure, a J.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Mechanistic Insights into the B(C₆F₅)₃-Initiated Aldehyde–Aniline–Alkyne Reaction To Form Substituted Quinolines

Fasano¹,

Radcliffe

Ingleson

2017

Organometallics

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“…N -Heterocycles 7 or 11 can be elaborated into other synthetically valuable products (Scheme ). SmI 2 -mediated reduction of the N−O bond in benzisoxazole 7a in the presence of acetophenone or acetone formed quinolines 12a and 12b . Palladium-catalyzed hydrogenolysis of the N−OMe bond present in 11q and 11p produced 1 H -indazole 13 and 2 H -pyrazole 14 .…”

mentioning

confidence: 99%

Intramolecular Fe(II)-Catalyzed N−O or N−N Bond Formation from Aryl Azides

et al. 2010

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Iron(II) bromide catalyzes the transformation of aryl-and vinyl azides with ketone-or methyl oxime substituents into 2,1-benzisoxazoles, indazoles or pyrazoles through the formation of an N-O or N-N bond. This transformation tolerates a variety of different functional groups to facilitate access to a range of benzisoxazoles or indazoles. The unreactivity of the Z-methyloxime indicates that N-heterocycle formation occurs through a nucleophilic attack of the ketone or oxime onto an activated planar iron azide complex.Despite the prevalence of nitrogen-heteroatom bonds in biologically active N-heterocycles, methods that form these bonds remain rare. 2,1-Benzisoxazoles1 , 2 or indazoles3 , 4 typically originate from starting materials with pre-existing N-O or N-N bonds such as oximes, nitrile oxides, or hydrazines. Direct construction of the N-O5 or N-N6 bond provides an attractive alternative approach to these N-heterocycles. Surprisingly, there are no prior examples of transition metal-catalyzed routes to these bonds even though such complexes promote the oxidation7 , 8 or imination9 of sulfides. Since we established that benzimidazoles could be produced from N-aryl imines with ortho-azido substituents upon exposure to FeBr 2 (Scheme 1),10 we were curious if nitrogen-heteroatom bond formation could be achieved by transposing the ortho-heteroatom substituent from the α-position to the β-position. While thermolysis of 3 affords the new nitrogen-heteroatom bond,5a-b , 6a-c the high temperature limits the functional group tolerated in the reaction. Herein, we report that iron(II) bromide catalyzes the formation of N-O or N-N bonds to transform azides 1 into 2,1-benzisoxazoles 4 or pyrazoles 5 under markedly benign conditions. To achieve transition metal-catalyzed nitrogen-heteroatom bond formation, the reactivity of 2-azidobenzophenone toward a variety of transition metal complexes was investigated (Table 1). This aryl azide is available in one step from commercially available 2-aminobenzophenone.11 While a plethora of methods have been reported to generate an electrophilic nitrogen atom from aryl azides,12 we found that only iron salts promoted 2,1-benzisoxazole 7a formation at significantly reduced temperatures. Screening other metal complexes known to decompose azides-including Cu(I)-and Cu(II) salts-did not result in nitrogen-oxygen bond formation.13 Our data suggests that the oxidation state of iron tgd@uic.edu. Supporting Information Available Complete experimental procedures, spectroscopic and analytical data for the products (PDF) is available free of charge via the Internet at http://pubs.acs.org. With these optimized conditions, the scope and limitations of iron(II)-catalyzed N-O bond formation was examined (Table 2).14 2,1-Benzisoxazole formation depended on the electronic nature of the azide. While the reaction tolerated R 1 -or R 2 -substituents, strong electron-withdrawing groups are incompatible with the reaction conditions (entries 1 -7). NIH Public AccessThe effect of the R 3 -substituent on t...

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Preparation of 2‐Aminobenzophenones and Polysubstituted Quinolines Through SmI₂ Promoted Reductive Cleavage of 3‐Aryl‐2,1‐benzisoxazoles.

Fan

Zhang

2006

ChemInform

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Arylbenzisoxazoles (I) undergo reductive cleavage of the N-O bond within a few minutes and afford aminobenzophenones (II) smoothly upon subsequent protonation. The preparation of polysubstituted quinolines such as (IV) and (VI) is possible by adding carbonyl compounds possessing an active methylene group, to the N-O cleaved intermediate, prior to protonation. -(FAN*, X.; ZHANG, X.; ZHANG, Y.; Heteroat. Chem. 16 (2005) 7, 637-643; Key Lab. Environ. Pollut. Control, Henan Norm. Univ., Henan 453002, Peop. Rep. China; Eng.) -H. Hoennerscheid 16-151

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Preparation of 2‐aminobenzophenones and polysubstituted quinolines through SmI₂ promoted reductive cleavage of 3‐aryl‐2,1‐benzisoxazoles

Cited by 9 publications

References 30 publications

Mechanistic Insights into the B(C₆F₅)₃-Initiated Aldehyde–Aniline–Alkyne Reaction To Form Substituted Quinolines

Mechanistic Insights into the B(C₆F₅)₃-Initiated Aldehyde–Aniline–Alkyne Reaction To Form Substituted Quinolines

Intramolecular Fe(II)-Catalyzed N−O or N−N Bond Formation from Aryl Azides

Preparation of 2‐Aminobenzophenones and Polysubstituted Quinolines Through SmI₂ Promoted Reductive Cleavage of 3‐Aryl‐2,1‐benzisoxazoles.

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Preparation of 2‐aminobenzophenones and polysubstituted quinolines through SmI2 promoted reductive cleavage of 3‐aryl‐2,1‐benzisoxazoles

Cited by 9 publications

References 30 publications

Mechanistic Insights into the B(C6F5)3-Initiated Aldehyde–Aniline–Alkyne Reaction To Form Substituted Quinolines

Mechanistic Insights into the B(C6F5)3-Initiated Aldehyde–Aniline–Alkyne Reaction To Form Substituted Quinolines

Intramolecular Fe(II)-Catalyzed N−O or N−N Bond Formation from Aryl Azides

Preparation of 2‐Aminobenzophenones and Polysubstituted Quinolines Through SmI2 Promoted Reductive Cleavage of 3‐Aryl‐2,1‐benzisoxazoles.

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Preparation of 2‐aminobenzophenones and polysubstituted quinolines through SmI₂ promoted reductive cleavage of 3‐aryl‐2,1‐benzisoxazoles

Mechanistic Insights into the B(C₆F₅)₃-Initiated Aldehyde–Aniline–Alkyne Reaction To Form Substituted Quinolines

Mechanistic Insights into the B(C₆F₅)₃-Initiated Aldehyde–Aniline–Alkyne Reaction To Form Substituted Quinolines

Preparation of 2‐Aminobenzophenones and Polysubstituted Quinolines Through SmI₂ Promoted Reductive Cleavage of 3‐Aryl‐2,1‐benzisoxazoles.