A highly enantioselective 1,3-dipolar cycloaddition reaction in alcoholic media: Ni(II)-pybox-tipsom catalyst

Iwasa, Seiji; Maeda, Hiroyuki; Nishiyama, Kohei; Tsushima, Shinji; Tsukamoto, Yasuyuki; Nishiyama, Hisao

doi:10.1016/s0040-4020(02)00978-x

Cited by 37 publications

(18 citation statements)

References 49 publications

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“…Although amine activation of enals5 has emerged as an attractive approach, most methods rely on the use of Lewis acids to activate the enoyl system toward the nitrone counterpart 3. 4, 6 However, despite the many applications, success in asymmetric nitrone cycloadditions remains very scarce compared to that reached in the parent Diels–Alder cycloaddition and only a limited number of alkene templates such as N ‐enoyl derivatives of oxazolidinone,4a–c, 6c–6g thiazolidinethione,6a pyrrolidinone,6b and pyrazolidinone,6h as well as certain alkylidene malonates6i have been employed to fulfill this gap. In metal‐catalyzed nitrone cycloadditions, not only are bidentate alkene substrates required but also metal–substrate coordination needs to be notably efficient for optimum selectivity 7.…”

Section: Methodsmentioning

confidence: 89%

Lewis Acid Catalyzed Asymmetric Cycloadditions of Nitrones: α′‐Hydroxy Enones as Efficient Reaction Partners

et al. 2005

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Dedicated to Professor J. Plumet on the occasion of his 60th birthdayThe 1,3-dipolar cycloaddition of nitrones to alkenes [1] is an atom-economic method for the construction of isoxazolidines, which are important precursors of, for example, alkaloids, amino acids, b-lactams, and amino sugars.[2] Typically, an electron-deficient alkene is involved, with the interaction between the LUMO of the alkene and the HOMO of the nitrone being the determinant for the relative orientation of the reactants. However, steric factors often counterbalance the electronic preferences, particularly in b-unsubstituted enoyl (acryloyl) systems, and make regiocontrol challenging. [3,4] Additionally, both endo/exo and p-facial selectivity have to be addressed. Although amine activation of enals [5] has emerged as an attractive approach, most methods rely on the use of Lewis acids to activate the enoyl system toward the nitrone counterpart. [3,4,6] However, despite the many applications, success in asymmetric nitrone cycloadditions remains very scarce compared to that reached in the parent DielsAlder cycloaddition and only a limited number of alkene templates such as N-enoyl derivatives of oxazolidinone, [4a-c, 6c-6g] thiazolidinethione, [6a] pyrrolidinone, [6b] and pyrazolidinone, [6h] as well as certain alkylidene malonates [6i] have been employed to fulfill this gap. In metal-catalyzed nitrone cycloadditions, not only are bidentate alkene substrates required but also metal-substrate coordination needs to be notably efficient for optimum selectivity. [7] We report herein that excellent combined levels of regio-, endo/exo-, and enantioselectivity may be achieved by using a'-hydroxy enones as new partners for this reaction.Recent observations from these laboratories in the context of Diels-Alder and conjugate addition reactions have shown the role of a'-hydroxy enones in metal-assisted activation, which likely occurs through formation of 1,4-metal-chelated species as the reactive intermediates.[8] It was argued that such a complexation pattern might be effective in nitrone cycloadditions and hence increase the pool of available templates for this reaction. To evaluate this assumption, initial screening reactions were carried out with the chiral a'-hydroxy enone 1 [9] and nitrone 3 a in the presence of several metal triflates (Scheme 1 and Table 1). Data revealed that Cu(OTf) 2 gave the best results and isoxazolidine 4 a could indeed be obtained in high yield and, most notably, with essentially perfect regio-and diastereoselectivity.Gratifyingly, the chemical efficiency and the high degree of regio-and stereocontrol for this Cu(OTf) 2 -mediated reaction was found to be quite general over the range of nitrones 3 a-k examined (Table 2). Nitrones bearing electronrich, electron-neutral, or electron-poor aryl substituents were tolerated with almost equal efficiency to give isoxazolidines 4 a-k in good yields and with diastereomeric ratios ranging Scheme 1. Regio-and stereocontrolled 1,3-dipolar cycloadditions of nitrones to a'-hydroxy enon...

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Section: Methodsmentioning

confidence: 89%

Lewis Acid Catalyzed Asymmetric Cycloadditions of Nitrones: α′‐Hydroxy Enones as Efficient Reaction Partners

et al. 2005

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“…The series of "tunable" chiral silyloxymethyl-pybox ligands (53a-c), in combination with the Ni(ClO 4 ) 2 , were found to catalyze 1,3dipolar cycloaddition of nitrones and 3-alkenoyl-2oxazolidinones in mostly excellent yields and remarkably high endo diastereoselectivities (mostly over 98 %) and enantioselectivities (92 to more than 99 % ee) (Fig. When dichloromethane was replaced by the environmentally friendly t-butanol as the solvent, the cycloadditions were found to proceed much faster, with no solvolysis product detected and the excellent levels of diastereo-and enantioselectivities retained [372]. When dichloromethane was replaced by the environmentally friendly t-butanol as the solvent, the cycloadditions were found to proceed much faster, with no solvolysis product detected and the excellent levels of diastereo-and enantioselectivities retained [372].…”

Section: Five-membered Heterocyclesmentioning

confidence: 99%

Recent Advances in Catalytic Asymmetric Addition to Imines and Related C=N Systems

Vilaivan¹,

Bhanthumnavin²,

Sritana-anant

2005

COC

150

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Addition reactions to imines are relatively less developed compared to those of carbonyl compounds due to low electrophilicity and ease of α-deprotonation. With the use of an appropriate activator, which can coordinate to the imine nitrogen atom, the electrophilicity of the imine can be enhanced and a range of nucleophilic addition reactions becomes possible. When the activator is chiral, it will also create chiral environment and will direct the approach of the nucleophile to one face of the imine over the other resulting in enantioselectivity. The potential of catalytic asymmetric addition to imines in organic synthesis is enormous, but is relatively underused. With the development of many highly effective chiral catalysts for imine additions, the situation will soon be changed. The present review will cover selected literature on catalytic asymmetric additions to aldimines, ketimines and related compounds including hydrazones, oximes and nitrones from 1999 to 2004. The reactions of interest include hydrogenation, alkylation, Mannich and related reactions such as aza-Baylis-Hillman and aza-Henry reaction, Strecker reaction, hydrophosphonylation, and 3-6 membered ring forming reactions from imines. Some applications of these methodologies in synthesis of nitrogen-containing biologically active compounds will also be presented.

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“…The Ni(II)/pybox catalyst used in these reactions is typically prepared in the presence of MS4A at 40 C prior to the catalytic reactions. Subsequently, a modified system of these cycloaddition reactions has been developed to conduct the reaction in an alcoholic medium (t-BuOH), obtaining similar results as in dichloromethane [59].…”

Section: 52mentioning

confidence: 99%

Asymmetric Synthesis

Shintani

Hayashi

2005

Modern Organonickel Chemistry

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The Cross-coupling ReactionTransition metal-catalyzed cross-coupling reactions represent a powerful approach for the construction of carbon-carbon bonds. As a result, these processes have been widely studied during the past few decades. Among the transition metals employed, the majority of the investigations have focused on nickel-and palladiumcatalyzed cross-couplings of aryl and alkenyl halides with various organometallic reagents [1]. In addition to the simple, nonasymmetric cross-coupling reactions, the enantioselective variants of these have also been the topics of interest in organic and organometallic chemistry [2].During the late 1970s and early 1980s, nickel-catalyzed asymmetric crosscoupling reactions of 1-arylethylmagnesium chlorides with vinyl bromide were described in the presence of chiral phosphine ligands [3]. It was first demonstrated that NiCl 2 /9.1 catalyzed the coupling reactions efficiently, affording the products in good enantiomeric excess (ee) (Scheme 9.1). The prerequisite of these reactions Modern Organonickel Chemistry. Edited by Y. Tamaru

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A highly enantioselective 1,3-dipolar cycloaddition reaction in alcoholic media: Ni(II)-pybox-tipsom catalyst

Cited by 37 publications

References 49 publications

Lewis Acid Catalyzed Asymmetric Cycloadditions of Nitrones: α′‐Hydroxy Enones as Efficient Reaction Partners

Lewis Acid Catalyzed Asymmetric Cycloadditions of Nitrones: α′‐Hydroxy Enones as Efficient Reaction Partners

Recent Advances in Catalytic Asymmetric Addition to Imines and Related C=N Systems

Asymmetric Synthesis

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