The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Rui Fausto - One of the best experts on this subject based on the ideXlab platform.
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on the photochemistry of 1 2 benzisoxazole capture of elusive spiro 2h azirine and ketenimine intermediates
European Journal of Organic Chemistry, 2016Co-Authors: Claudio M Nunes, Sandra Pinto, Igor Reva, Rui FaustoAbstract:The photochemistry of 1,2-benzisoxazole (1) was studied using low-temperature matrix isolation coupled with infrared spectroscopy and quantum chemistry calculations. We identified, for the first time, spiro-2H-azirine 2 and ketenimine 3 as intermediates in the photoisomerization of 1 to 2-cyanophenol (4). These results constitute indirect evidence for the existence of vinylnitrene intermediates in the photochemistry of 1,2-Benzisoxazoles. The potential energy surface (PES) resulting from the N–O bond cleavage of 1 was compared with the respective PES of the parent isoxazole. Calculations at the CBS-QB3 level show that no stabilization is gained for the triplet vinylnitrene upon introduction of a benzene ring fused with isoxazole. However, the energies of 2 and 3 are higher by 13–15 kcal/mol comparing with the 2H-azirine and ketenimine analogs resulting from isoxazole, which explains why they had not been observed before. Our general mechanistic proposal also predicts well the photoisomerizations of 2 and 3 to 4.
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Photochemistry of 3-amino-1,2-benzisoxazole: unexpected photoisomerization of an amino-spiro-2H-azirine to a 1H-diazirine
Tetrahedron Letters, 2016Co-Authors: Claudio M Nunes, Sandra Pinto, Igor Reva, Rui FaustoAbstract:Abstract UV irradiation of 3-amino-1,2-benzisoxazole isolated in an argon matrix leads to the formation of an amino-spiro-2 H -azirine. The amino-spiro-2 H -azirine was found to photoisomerize back to 3-amino-1,2-benzisoxazole and also to a 1 H -diazirine, which isomerizes to a carbodiimide. All the reported species were characterized experimentally by IR spectroscopy and confirmed by comparison with theoretical IR spectra. The discovery of the transformation of an amino-spiro-2 H -azirine into a 1 H -diazirine is unprecedented in the chemistry of reactive intermediates.
Yefeng Tang - One of the best experts on this subject based on the ideXlab platform.
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Rh(II)-Catalyzed Transannulation of N-Sulfonyl-1,2,3-Triazoles with 2,1-Benzisoxazoles or 1,2-Benzisoxazoles
Organic letters, 2016Co-Authors: Xiaoqiang Lei, Mohan Gao, Yefeng TangAbstract:A Rh(II)-catalyzed transannulation of N-sulfonyl-1,2,3-triazoles with 2,1-Benzisoxazoles has been developed, which affords an efficient method for the synthesis of quinazoline derivatives. The transformation represents an unprecedented example which utilizes N-sulfonyl-1,2,3-triazole as an aza-[2C]-component in cycloadditions. Meanwhile, a Rh(II)-catalyzed formal [3 + 2] cycloaddition of N-sulfonyl-1,2,3-triazoles with 1,2-Benzisoxazoles is also presented, which enables the rapid synthesis of functionalized imidazole derivatives.
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Rh(II)-Catalyzed Transannulation of N‑Sulfonyl-1,2,3-Triazoles with 2,1-Benzisoxazoles or 1,2-Benzisoxazoles
2016Co-Authors: Xiaoqiang Lei, Mohan Gao, Yefeng TangAbstract:A Rh(II)-catalyzed transannulation of N-sulfonyl-1,2,3-triazoles with 2,1-Benzisoxazoles has been developed, which affords an efficient method for the synthesis of quinazoline derivatives. The transformation represents an unprecedented example which utilizes N-sulfonyl-1,2,3-triazole as an aza-[2C]-component in cycloadditions. Meanwhile, a Rh(II)-catalyzed formal [3 + 2] cycloaddition of N-sulfonyl-1,2,3-triazoles with 1,2-Benzisoxazoles is also presented, which enables the rapid synthesis of functionalized imidazole derivatives
Rai-shung Liu - One of the best experts on this subject based on the ideXlab platform.
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gold catalyzed michael type reactions and 4 2 annulations between propiolates and 1 2 Benzisoxazoles with ester directed chemoselectivity
Organic Letters, 2018Co-Authors: Yashwant Bhaskar Pandit, Rajkumar Lalji Sahani, Rai-shung LiuAbstract:This work reports gold-catalyzed reactions between 1,2-Benzisoxazoles and propiolate derivatives with ester-controlled chemoselectivity. For ethyl propiolates 1′, their gold-catalyzed reactions afforded Michael-type products 4, whereas tert-butyl propiolates 1 preferably underwent [4 + 2]-annulations, further yielding 6H-1,3-oxazin-6-one derivatives 3.
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gold catalyzed 5 2 and 5 1 annulations between ynamides and 1 2 Benzisoxazoles with ligand controlled chemoselectivity
ACS Catalysis, 2018Co-Authors: Prakash D Jadhav, Rai-shung LiuAbstract:This work describes two distinct annulations between ynamides and 1,2-Benzisoxazoles with chemoselectivity controlled by ligands. With IPrAuCl/AgNTf2, aryl-substituted ynamides undergo [5+2]-annulation reactions, whereas P(t-Bu)2(o-biphenyl)AuCl/AgNTf2 alters the chemoselectivity of the same ynamides to implement [5+1]-annulation reactions. 13C-Labeling experiments confirm that a 1,2-sulfonamide shift is involved in the [5+1]-annulation process. A plausible mechanism is postulated to rationalize the mechanisms of the two annulations.
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gold catalyzed 4 2 annulations between α alkyl alkenylgold carbenes and Benzisoxazoles with reactive alkyl groups
Chemical Science, 2018Co-Authors: Bhanudas Dattatray Mokar, Prakash D Jadhav, Yashwant Bhaskar Pandit, Rai-shung LiuAbstract:This work reports new (4 + 2)-annulations of α-alkyl vinylgold carbenes with Benzisoxazoles to afford 3,4-dihydroquinoline derivatives with high anti-stereoselectivity. The annulations are operable with carbenes in both acyclic and cyclic forms. This reaction sequence involves an initial formation of imines from α-alkylgold carbenes and Benzisoxazoles, followed by a novel carbonyl-enamine reaction to yield 3,4-dihydroquinoline derivatives. This system presents the first alkyl C–H reactivity of α-alkyl gold carbenes with an external substrate.
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Gold-Catalyzed [4 + 1]-Annulation Reactions between 1,4-Diyn-3-ols and Isoxazoles To Construct a Pyrrole Core
2018Co-Authors: Rahul Dadabhau Kardile, Balaji S. Kale, Pankaj Sharma, Rai-shung LiuAbstract:This work reports gold-catalyzed [4 + 1]-annulation reactions between 1,4-diyn-3-ols and isoxazoles or Benzisoxazoles to yield pyrrole derivatives. The reaction chemoselectivity is controlled by an initial attack of an isoxazole at a less hindered alkyne to form gold carbenes, further inducing a 1,2-migration of a second alkyne group. A broad substrate scope of 1,4-diyn-3-ols, isoxazoles and even Benzisoxazoles highlighted the reaction utility
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Gold-Catalyzed Michael-Type Reactions and [4 + 2]-Annulations between Propiolates and 1,2-Benzisoxazoles with Ester-Directed Chemoselectivity
2018Co-Authors: Yashwant Bhaskar Pandit, Rajkumar Lalji Sahani, Rai-shung LiuAbstract:This work reports gold-catalyzed reactions between 1,2-Benzisoxazoles and propiolate derivatives with ester-controlled chemoselectivity. For ethyl propiolates 1′, their gold-catalyzed reactions afforded Michael-type products 4, whereas tert-butyl propiolates 1 preferably underwent [4 + 2]-annulations, further yielding 6H-1,3-oxazin-6-one derivatives 3
Yongmin Zhang - One of the best experts on this subject based on the ideXlab platform.
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smi2 mediated facile one pot preparation of 2 4 diarylquinolines from 3 aryl 2 1 Benzisoxazoles
Tetrahedron Letters, 2002Co-Authors: Xuesen Fan, Yongmin ZhangAbstract:Abstract On treatment with SmI 2 , 3-aryl-2,1-Benzisoxazoles undergo reductive cleavage of the NO bond leading to 2-aminobenzophenones in high yields upon protonation. If aryl methyl ketones are added to the reaction mixture prior to protonation, the desired 2,4-diarylquinolines can be obtained in moderate yields under mild conditions.
Paulo Almeida - One of the best experts on this subject based on the ideXlab platform.
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the synthesis of 2 spiroindolin 3 one thio barbiturates from 2 1 Benzisoxazoles a rearrangement promoted by thermal conditions
Synthesis, 2020Co-Authors: Pedro F. Soeiro, João L. Serrano, Samuel Silvestre, Renato E. F. Boto, J A Paixao, Paulo AlmeidaAbstract:A new thermal process to prepare spiroindolin-3-ones from 3-substituted 2,1-Benzisoxazoles in good yields (70–85%) is described. The highest yields were observed when microwave irradiation was used. The method does not require the use of any additive or catalyst. A possible reaction mechanism involving a nitrene key intermediate is proposed.
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Synthesis and process optimization of symmetric and unsymmetric barbiturates C5-coupled with 2,1-Benzisoxazoles
Molecular Diversity, 2020Co-Authors: João L. Serrano, Samuel Silvestre, Pedro F. Soeiro, Melani A. Reis, Renato E. F. Boto, Paulo AlmeidaAbstract:Benzisoxazoles represent an important pharmacophore in medicinal chemistry. Recently, an unexpected formation of symmetric 3-substituted 2,1-Benzisoxazoles through reduction of 5-(2-nitrobenzylidene)barbiturates has been described. This reductive intramolecular heterocyclization probably involves a nitroso intermediary. To improve the previous reaction conditions, the nature of the reducing agent and additives, reaction time and solvents were evaluated. By applying the optimized conditions, several symmetric and unsymmetric barbiturates C5-coupled with 2,1-Benzisoxazoles were prepared with an yield of 52–87%. From this set, seven compounds were novel and the unsymmetric nature of the (thio)barbituric acid moiety was explored. For that, the total synthesis, starting from the respective urea or thiourea, was successfully performed, and 11 thiobarbiturates, benzylidene barbiturate and thiobarbiturate precursors are described. Graphical abstract
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A synthetic route to novel 3-substituted-2,1-Benzisoxazoles from 5-(2-nitrobenzylidene)(thio)barbiturates
Comptes Rendus Chimie, 2017Co-Authors: João L. Serrano, Eunice Cavalheiro, Sónia Barroso, Maria João Romão, Samuel Silvestre, Paulo AlmeidaAbstract:Abstract 2,1-Benzisoxazoles, also called anthranils, are one of the two types of aromatic bicyclic heterocycles having a benzene ring fused with an isoxazole, which are particularly recognized as valuable intermediates in organic synthesis. Nevertheless several methods can be found in the literature to prepare 2,1-Benzisoxazoles, we herein report a new, efficient, simple, mild, and alternative procedure to prepare 3-substituted-2,1-Benzisoxazoles from 5-(2-nitrobenzylidene)barbiturates in moderate to good yields (51–82%). All the novel Benzisoxazoles showed spectral data fully consistent with the assigned structures, which were unequivocally confirmed by single crystal X-ray analysis. A possible mechanism of the reaction is proposed. In addition, a screening of the bioactivity of these Benzisoxazoles as xanthine oxidase inhibitors, antioxidants, and cytotoxic compounds was performed. The benzisoxazole formed from barbituric acid revealed moderate xanthine oxidase inhibitory effects (IC50 = 22.10 μM).