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Jiaxi Xu - One of the best experts on this subject based on the ideXlab platform.
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Theoretical studies on selectivities in the Staudinger Reaction of vicinal diimines and ketenes.
Science China-chemistry, 2012Co-Authors: Xinyao Li, Jiaxi XuAbstract:The selectivities, including peri-, regio-, and diastereoselectivities, in the Staudinger Reaction involving vicinal diimines and ketenes were investigated theoretically via the density functional theory (DFT) calculation. The results indicate that vicinal diimines prefer stepwise [2+2] cycloaddition rather than [2+4] cycloaddition to generate cis-4-imino-β-lactams. The diimines attack the less sterically hindered exo-side of ketenes to generate zwitterionic intermediates, which directly undergo a conrotatory ring closure to produce cis-4-imino-β-lactams whatever diimines with less or more bulky N-substituents. For unsymmetric vicinal ketoaldehyde-derived diimines, their ketimines attack the exo-side of ketenes and undergo a conrotatory ring closure to produce cis-4-aldimino-β-lactams due to less steric effect. The current theoretical studies provide very important information for in-depth understanding of the selective formation of mono-cis-β-lactams from vicinal diimines and ketenes.
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Remarkable ketene substituent dependent effect of photo irradiation on the diastereoselectivity in the Staudinger Reaction
Tetrahedron Letters, 2012Co-Authors: Zhanhui Yang, Jiaxi XuAbstract:Abstract Controlling diastereoselectivity is a challenging issue in the Staudinger Reaction. The influence of ultraviolet irradiation on the stereoselectivity in the Staudinger Reaction has been investigated. The results indicate that ultraviolet irradiation is one of the most important means to regulate the diastereoselectivity of the products in the Staudinger Reaction, whatever ketenes were generated from diazomethyl ketones or from substituted acetyl chlorides in the presence of triethylamine. However, the regulation is dependent on the ketene substituents obviously. Ultraviolet irradiation can even reverse the diastereoselectivity for the Reactions involving ketenes without strong electron-donating substituents.
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Synthesis of 3‐Alkoxy/Aryloxy‐β‐lactams Using Diazoacetate Esters as Ketene Precursors under Photoirradiation.
ChemInform, 2011Co-Authors: Hengzhen Qi, Zhanhui Yang, Jiaxi XuAbstract:The trans-β-lactams, e.g. (III), are obtained via Staudinger Reaction under metal-free and neutral conditions.
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new insights into the torquoselectivity of the Staudinger Reaction
Journal of the American Chemical Society, 2009Co-Authors: Yong Liang, Lei Jiao, Shiwei Zhang, Zhixiang Yu, Jiaxi XuAbstract:To understand the torquoselectivity and the electronic effects of the Staudinger Reaction, a study using a combination of experiments and DFT calculations has been conducted for the Reactions of an unsymmetric cyclic ketene and cyclic imines with different electronic properties. The predominant formation of the donor-in β-lactams, the torquoelectronically disfavored products, was observed for the first time. The Hammett analyses reveal a close relationship between the donor-out/donor-in product ratio and the electronic nature of the imines. The kinetic competition experiments and DFT calculations indicate that the two-step Staudinger Reaction shows different rate-determining steps in the donor-in and donor-out pathways. Our investigations reveal that the torquoelectronic control in the Staudinger Reaction is quite different from that in the ring-opening Reaction of cyclobutene derivatives. The diastereoselectivity of the Staudinger Reaction involving an unsymmetric disubstituted ketene cannot be simply ra...
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diastereoselectivity in the Staudinger Reaction a useful probe for investigation of nonthermal microwave effects
Tetrahedron, 2007Co-Authors: Libo Hu, Daming Du, Yikai Wang, Bonan Li, Jiaxi XuAbstract:Abstract The effect of microwave irradiation on the selectivity, especially stereoselectivity, is one of the most important issues in microwave-assisted organic Reactions. The diastereoselectivity in Staudinger Reactions involving the representative ketenes and the corresponding matched imines has been used as a probe to investigate carefully the existence of the specific nonthermal microwave effects. The results indicate that the microwave irradiation-controlled stereoselectivity in the Staudinger Reaction is in fact the contribution of temperature. No specific nonthermal microwave effect was found in the Staudinger Reaction.
Pedro Molina - One of the best experts on this subject based on the ideXlab platform.
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trapping of a phosphazide intermediate in the Staudinger Reaction of tertiary phosphines with azides and its application to the synthesis of analogs of the marine alkaloid midpacamide
Tetrahedron Letters, 2004Co-Authors: Pilar M Fresneda, Miguel A Sanz, Marta Castaneda, Pedro MolinaAbstract:Abstract A new method based on the Reaction of an E-phosphazide, an intermediate in the Staudinger Reaction between triphenylphosphine with an azide, with heterocumulenes allows the one-pot, two-component synthesis of a number of analogs of the pyrrole–imidazole marine alkaloid midpacamide. The procedure, which involves sequential treatment of the appropriate α-azido ester with triphenylphosphine and isothiocyanate leads to the thiohydantoin product after aqueous workup. The cyclization conditions can also be adapted to the synthesis of hydantoins by using isocyanates.
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isolation reactivity and intramolecular trapping of phosphazide intermediates in the Staudinger Reaction of tertiary phosphines with azides
Tetrahedron, 2000Co-Authors: Desamparados M Velasco, Pedro Molina, Pilar M Fresneda, Miguel A SanzAbstract:Abstract The Staudinger Reaction of the N -substituted o -azidobenzamide 1 with triphenylphosphine or diphenylmethylphosphine allows the isolation of the intermediate phosphazides as crystalline solids, which have been characterized by spectroscopic methods. These compounds react in aza Wittig type fashion with isocyanates to give unexpectedly the corresponding 1,2,3-benzotriazinone derivative. Trapping of a Z -phosphazide by intramolecular aza Wittig Reaction is reported for the first time.
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Unexpected Staudinger Reaction of α-azidoacetonitriles α-phenyl substituted with triphenylphosphine. Preparation, X-ray crystal and molecular structures of a phosphazine, an aminophosphonium carbanion salt and a phosphazide, with (Z)-configuration
Tetrahedron, 1996Co-Authors: Pedro Molina, Carmen López-leonardo, Javier Llamas-botía, Concepción Foces-foces, Cristina Fernández-castañoAbstract:Abstract Staudinger Reaction of α-azidophenylacetonitrile with triphenylphosphine in 1:2 molar ratio provides the triphenylphosphazine 4 derived from α-diazophenylacetonitrile, whereas in 2:1 molar ratio the final product is found to be the aminotriphenylphosphonium salt of phenylmalononitrile 6 . However, the Staudinger Reaction of α-azidodiphenylacetonitrile with triphenylphosphine affords the corresponding (Z)-phosphazide 17 . The crystal and molecular structures of compounds 4,6 , and 17 have been determined by X-ray analysis. Compound 17 is the first isolated phosphazide which presents the (Z)-configuration with respect to the central N-N bond of the PN 3 C moiety (P-N-N-N=0.0(3)°).
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Unexpected Staudinger Reaction of α-azidophenylacetonitrile and triphenylphosphine: synthesis and crystal structure of aminotriphenylphosphonium salt of phenylmalononitrile
Journal of The Chemical Society Chemical Communications, 1995Co-Authors: Pedro Molina, Carmen López-leonardo, Javier Llamas-botía, Concepción Foces-foces, Cristina Fernández-castañoAbstract:Staudinger Reaction of α-azidophenyiacetonitrile with triphenylphosphine in 1:2 molar ratio provides the triphenylphosphinazine derived from α-diazophenylacetonitrile, whereas in 2:1 molar ratio the final product is found to be the aminotriphenylphosphonium salt of phenylmalononitrile; X-ray structure analysis of this salt indicates that the anion and cation interact with one another via hydrogen bonding.
Frederick F Becker - One of the best experts on this subject based on the ideXlab platform.
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asymmetric synthesis of anticancer β lactams via Staudinger Reaction utilization of chiral ketene from carbohydrate
European Journal of Medicinal Chemistry, 2010Co-Authors: Bimal K. Banik, Indrani Banik, Frederick F BeckerAbstract:We describe herein asymmetric synthesis of a novel anticancer β-lactam following Staudinger Reaction with chiral carbohydrate as the ketene component with an achiral imine. The in vitro cytotoxicity studies of these β-lactams are also reported here.
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stereocontrolled synthesis of anticancer β lactams via the Staudinger Reaction
Bioorganic & Medicinal Chemistry, 2005Co-Authors: Bimal K. Banik, Indrani Banik, Frederick F BeckerAbstract:Stereocontrolled synthesis of novel β-lactams using polyaromatic imines following the Staudinger Reaction has been accomplished. The effects of domestic microwave irradiation on this type of Reaction have been investigated. Formation of trans-β-lactams has been explained through isomerization of the enolates formed during the Reaction of acid chloride (equivalent) with imines in the presence of triethylamine. A donor–acceptor complex pathway is believed to be involved in the formation of cis-β-lactams. The effect of a peri hydrogen has been found to be significant in controlling the stereochemistry of the resulting β-lactams. SAR has identified β-lactams with anticancer activity. The presence of an acetoxy group has proven obligatory for their anticancer activity.
Yikai Wang - One of the best experts on this subject based on the ideXlab platform.
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diastereoselectivity in the Staudinger Reaction a useful probe for investigation of nonthermal microwave effects
Tetrahedron, 2007Co-Authors: Libo Hu, Daming Du, Yikai Wang, Bonan Li, Jiaxi XuAbstract:Abstract The effect of microwave irradiation on the selectivity, especially stereoselectivity, is one of the most important issues in microwave-assisted organic Reactions. The diastereoselectivity in Staudinger Reactions involving the representative ketenes and the corresponding matched imines has been used as a probe to investigate carefully the existence of the specific nonthermal microwave effects. The results indicate that the microwave irradiation-controlled stereoselectivity in the Staudinger Reaction is in fact the contribution of temperature. No specific nonthermal microwave effect was found in the Staudinger Reaction.
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notable and obvious ketene substituent dependent effect of temperature on the stereoselectivity in the Staudinger Reaction
Journal of Organic Chemistry, 2007Co-Authors: Bonan Li, Daming Du, Yikai Wang, Jiaxi XuAbstract:A notable and obvious ketene substituent-dependent effect of temperature on the stereoselectivity in the Staudinger Reaction was observed. Most Staudinger Reactions show concave Eyring plots characterized by two lines with an inversion point, following the principle of isoinversion. Their cis-selectivities decrease with increasing temperature. Reactions involving intramolecular p−π and π−π interactions between the ketene substituents and imine C-substituents reveal protruding, S-shaped or straight-line Eyring plots. Their cis-selectivities increase with increasing temperature in a certain temperature region because such interactions enhance the cis-selectivity. Staudinger Reactions involving cyclic imines with different ketenes clearly indicate that the temperature-dependent stereoselectivity is caused by the different rate increases of the direct ring closure, which are affected by the p−π and π−π interactions between ketene substituents and imine C-substituents if they exist, and the isomerization of th...
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do Reaction conditions affect the stereoselectivity in the Staudinger Reaction
Journal of Organic Chemistry, 2006Co-Authors: Yikai Wang, Yong Liang, Lei Jiao, Daming Du, Jiaxi XuAbstract:The stereochemistry is one of the critical issues in the Staudinger Reaction. We have proposed the origin of the stereoselectivity recently. The effects of solvents, additives, and pathways of ketene generation on the stereoselectivity were investigated by using a clean Staudinger Reaction, which is a sensitive Reaction system to the stereoselectivity. The results indicate that the additives, usually existed and generated in the Staudinger Reaction, and the pathways of the ketene generation do not generally affect the stereoselectivity. The solvent affects the stereoselectivity. The polar solvent is favorable to the formation of trans-β-lactams. The addition orders of the reagents affect the stereoselectivity in the Staudinger Reaction between acyl chlorides and imines. The addition of a tertiary amine into a solution of the acyl chloride and the imine generally decreases the stereoselectivity, which is affected by the interval between additions of the acyl chloride and the tertiary amine, and the imine s...
Daming Du - One of the best experts on this subject based on the ideXlab platform.
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diastereoselectivity in the Staudinger Reaction a useful probe for investigation of nonthermal microwave effects
Tetrahedron, 2007Co-Authors: Libo Hu, Daming Du, Yikai Wang, Bonan Li, Jiaxi XuAbstract:Abstract The effect of microwave irradiation on the selectivity, especially stereoselectivity, is one of the most important issues in microwave-assisted organic Reactions. The diastereoselectivity in Staudinger Reactions involving the representative ketenes and the corresponding matched imines has been used as a probe to investigate carefully the existence of the specific nonthermal microwave effects. The results indicate that the microwave irradiation-controlled stereoselectivity in the Staudinger Reaction is in fact the contribution of temperature. No specific nonthermal microwave effect was found in the Staudinger Reaction.
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notable and obvious ketene substituent dependent effect of temperature on the stereoselectivity in the Staudinger Reaction
Journal of Organic Chemistry, 2007Co-Authors: Bonan Li, Daming Du, Yikai Wang, Jiaxi XuAbstract:A notable and obvious ketene substituent-dependent effect of temperature on the stereoselectivity in the Staudinger Reaction was observed. Most Staudinger Reactions show concave Eyring plots characterized by two lines with an inversion point, following the principle of isoinversion. Their cis-selectivities decrease with increasing temperature. Reactions involving intramolecular p−π and π−π interactions between the ketene substituents and imine C-substituents reveal protruding, S-shaped or straight-line Eyring plots. Their cis-selectivities increase with increasing temperature in a certain temperature region because such interactions enhance the cis-selectivity. Staudinger Reactions involving cyclic imines with different ketenes clearly indicate that the temperature-dependent stereoselectivity is caused by the different rate increases of the direct ring closure, which are affected by the p−π and π−π interactions between ketene substituents and imine C-substituents if they exist, and the isomerization of th...
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do Reaction conditions affect the stereoselectivity in the Staudinger Reaction
Journal of Organic Chemistry, 2006Co-Authors: Yikai Wang, Yong Liang, Lei Jiao, Daming Du, Jiaxi XuAbstract:The stereochemistry is one of the critical issues in the Staudinger Reaction. We have proposed the origin of the stereoselectivity recently. The effects of solvents, additives, and pathways of ketene generation on the stereoselectivity were investigated by using a clean Staudinger Reaction, which is a sensitive Reaction system to the stereoselectivity. The results indicate that the additives, usually existed and generated in the Staudinger Reaction, and the pathways of the ketene generation do not generally affect the stereoselectivity. The solvent affects the stereoselectivity. The polar solvent is favorable to the formation of trans-β-lactams. The addition orders of the reagents affect the stereoselectivity in the Staudinger Reaction between acyl chlorides and imines. The addition of a tertiary amine into a solution of the acyl chloride and the imine generally decreases the stereoselectivity, which is affected by the interval between additions of the acyl chloride and the tertiary amine, and the imine s...
