Asymmetric addition of phenylzinc reagents to C-alkynyl nitrones. Enantiomeric enhancement by a product-like additive

Wei, Weilin; Hamamoto, Yoshihira; Ukaji, Yutaka; Inomata, Katsuhiko

doi:10.1016/j.tetasy.2008.01.029

Cited by 17 publications

(10 citation statements)

References 23 publications

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“…By employing a mixed zinc reagent, PhZnMe, the enantioselection increased up to 92% ee. [71] Boron derivatives are good precursors of arylzinc reagents. Thus, the diethylzinc-mediated addition of alkoxyboronates to chiral nitrones afforded hydroxylamines in high diastereomeric ratios.…”

Section: Organozinc Derivativesmentioning

confidence: 99%

“…Thus, the diethylzinc-mediated addition of alkoxyboronates to chiral nitrones afforded hydroxylamines in high diastereomeric ratios. [71] The reaction could also be promoted by chiral ligands (used in an excess of 1.3 eq) to give enantioselectivities up to 97-99%ee. [72] An enantioselective addition of substituted vinylzinc reagents (also prepared from the corresponding boranes) was achieved by using ligand 53.…”

Section: Organozinc Derivativesmentioning

confidence: 99%

See 1 more Smart Citation

Recent Advances in the Preparation of Enantiomerically Pure Hydroxylamines from Nitrones

Matute¹,

García‐Viñuales²,

Hayes³

et al. 2016

COS

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This review covers the recent advances in the synthesis of enantiomerically pure hydroxylamines employing nitrones as starting materials. Nucleophilic additions of organometallic reagents to nitrones are the most common way for introducing a hydroxyamino group into carbon skeletons with the concomitant formation of a new carbon-carbon bond. Addition of carbanions derived from enolates, cyanide or fluorinated derivatives allow the preparation of complex structures. Radical additions and, in particular samarium diiodide-mediated reductive coupling of nitrones with carbonyl compounds and α,β-unsaturated esters have also been considered. All these approaches provide efficient methods of preparation of enantiomerically pure hydroxylamienes that are valuable synthetic intermediates. KeywordsHydroxylamines; Nitrones; Organometallics; Mannich; Reductive coupling 2 Graphical Abstract 3

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Section: Organozinc Derivativesmentioning

confidence: 99%

Section: Organozinc Derivativesmentioning

confidence: 99%

Recent Advances in the Preparation of Enantiomerically Pure Hydroxylamines from Nitrones

Matute¹,

García‐Viñuales²,

Hayes³

et al. 2016

COS

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“…Modest yield was obtained using unsaturated ester 1i as substrate; in contrast, a trace amount of ketonitrone 3ja was observed when acrylamide 1j was subjected to the optimal conditions. Cinnamaldehyde 1k failed to yield the desired ketonitrone but gave the aldonitrone 3ka′ in a yield of 87%, perhaps due to the higher electrophilicity of aldehyde compared to the C–C triple bond in the structure of 1k . An array of substituents (R 3 ) were also examined, and all of the reactions proceeded smoothly to furnish the corresponding ketonitrones in 61–83% yields ( 3la – sa ); it is noteworthy that ketones bearing electron-withdrawing substituents gave slightly higher yields than ketones with electron-donating substituents ( 3la – na vs 3oa and 3pa ).…”

mentioning

confidence: 99%

Carbonyl-Directed Addition of N-Alkylhydroxylamines to Unactivated Alkynes: Regio- and Stereoselective Synthesis of Ketonitrones

et al. 2019

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A variety of ketonitrones were synthesized in moderate to excellent yields with high chemo-, regio-, and stereoselectivity by using carbonyl-directed addition of N-alkylhydroxylamines to unactivated alkynes under mild conditions. The product diverisity could be controlled by the use of different bases, and EtN(n-Pr)2 could promote the formation of ketonitrones while using EtONa as base led to indanone-derived nitrones. Control experiments indicated that the carbonyl group of the substrate acted as an H-bond acceptor except for an electron-withdrawing group, and conjugated enone skeleton accounted for the high selectivity.

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“…

Owing to the synthetic versatility and modularity of acetylenes, chiral building blocks bearing acetylene moieties are widely used as valuable intermediates. The asymmetric transition metal mediated addition of terminal acetylenes (asymmetric alkynylations) to various prochiral electrophiles (Scheme 1, left), [2] such as aldehydes, [3] ketones, [4] aldimines, [5] and electron-deficient alkenes, [6] as well as asymmetric additions to prochiral alkynyl substrates (Scheme 1, right), [7][8][9][10][11] have been successfully adopted for this purpose. The asymmetric transition metal mediated addition of terminal acetylenes (asymmetric alkynylations) to various prochiral electrophiles (Scheme 1, left), [2] such as aldehydes, [3] ketones, [4] aldimines, [5] and electron-deficient alkenes, [6] as well as asymmetric additions to prochiral alkynyl substrates (Scheme 1, right), [7][8][9][10][11] have been successfully adopted for this purpose.

…”

mentioning

confidence: 99%

“…[1] Accordingly, tremendous efforts have been devoted to the development of catalytic asymmetric approaches to enable facile access to these attractive materials. The asymmetric transition metal mediated addition of terminal acetylenes (asymmetric alkynylations) to various prochiral electrophiles (Scheme 1, left), [2] such as aldehydes, [3] ketones, [4] aldimines, [5] and electron-deficient alkenes, [6] as well as asymmetric additions to prochiral alkynyl substrates (Scheme 1, right), [7][8][9][10][11] have been successfully adopted for this purpose. [12,13] However, most of these procedures are only applicable to the synthesis of a-chiral acetylenes having one hydrogen atom at the a position.…”

mentioning

confidence: 99%

α‐Chiral Acetylenes Having an All‐Carbon Quaternary Center: Phase Transfer Catalyzed Enantioselective α Alkylation of α‐Alkyl‐α‐alkynyl Esters

2009

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Owing to the synthetic versatility and modularity of acetylenes, chiral building blocks bearing acetylene moieties are widely used as valuable intermediates. [1] Accordingly, tremendous efforts have been devoted to the development of catalytic asymmetric approaches to enable facile access to these attractive materials. The asymmetric transition metal mediated addition of terminal acetylenes (asymmetric alkynylations) to various prochiral electrophiles (Scheme 1, left), [2] such as aldehydes, [3] ketones, [4] aldimines, [5] and electron-deficient alkenes, [6] as well as asymmetric additions to prochiral alkynyl substrates (Scheme 1, right), [7][8][9][10][11] have been successfully adopted for this purpose. [12,13] However, most of these procedures are only applicable to the synthesis of a-chiral acetylenes having one hydrogen atom at the a position. [14] We envisaged that asymmetric a functionalization of racemic a-alkyl-a-alkynyl esters via prochiral a-alkynyl enolates would offer a distinctive solution in this realm, providing a-chiral acetylenes having a quaternary stereogenic center (Scheme 2). The asymmetric C À C bond formation with these substrates is highly appealing since it is expected to generate an enantioenriched all-carbon quaternary center having both an appended acetylene and ester as useful functionalities; [15] such a substrate is hardly accessible by use of the existing catalytic asymmetric methods.As a suitable benchmark catalytic system to evaluate the viability of such a transformation, we selected phase transfer catalyzed asymmetric alkylation, taking advantage of its wellestablished practicality in analogous transformations, as well as our broad interest in phase-transfer catalysis. [16] The starting materials, a-alkyl-a-alkynyl esters, could be synthesized from a-iodoalkanoates and monosubstituted acetylenes by using the protocol reported by Oshima and co-workers. [17] In an exploratory study, the asymmetric benzylation of the a-silylethynyl esters 3 was investigated under conventional phase transfer catalyzed alkylation reaction conditions using (S)-1 a as the catalyst (Table 1). [18] To our delight, the reaction of a-(tert-butyldimethylsilyl)ethynyl ester cleanly provided the desired compound in 87 % yield with 63 % ee (Table 1, entry 1). Examination of the steric Scheme 1. Common tactics for the catalytic asymmetric synthesis of a-chiral acetylenes.Scheme 2. Phase transfer catalyzed asymmetric functionalization of a-alkyl-a-alkynyl esters. Q = ammonium. Table 1: Screening of the reaction conditions. [a] Entry Cat. Si Solvent T [8C], t [h] Yield [%] [b] ee [%] [c]

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Asymmetric addition of phenylzinc reagents to C-alkynyl nitrones. Enantiomeric enhancement by a product-like additive

Cited by 17 publications

References 23 publications

Recent Advances in the Preparation of Enantiomerically Pure Hydroxylamines from Nitrones

Recent Advances in the Preparation of Enantiomerically Pure Hydroxylamines from Nitrones

Carbonyl-Directed Addition of N-Alkylhydroxylamines to Unactivated Alkynes: Regio- and Stereoselective Synthesis of Ketonitrones

α‐Chiral Acetylenes Having an All‐Carbon Quaternary Center: Phase Transfer Catalyzed Enantioselective α Alkylation of α‐Alkyl‐α‐alkynyl Esters

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