Studies on the niobium pentachloride-mediated nucleophilic additions to an enantiopure cyclic N-acyliminium ion derived from (S)-malic acid

Andrade, Carlos Kleber Z.; Rocha, Rafael O.; Russowsky, Dennis; Godoy, Marla N.

doi:10.1590/s0103-50532005000400007

Cited by 4 publications

(4 citation statements)

References 7 publications

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“…As highlighted in Scheme , addition of allyltrimethylsilane to the known enantiopure 3b according to our protocol effectively provides allylation in 82% yield while providing the desired product as a mixture of two inseparable diastereomers 4bA and 4bB in a 70:30 ratio. This stereochemical outcome at C 2 is similar to that reported in the literature for the same reactant 3b using other Lewis acids such as BF 3 ·Et 2 O, InCl 3 ,19a NbCl 5 ,19b as well as TMSOTf, 9d, and Sc(OTf) 3 for related structures 10a. Interestingly, it has been reported also that enantiopure N -acyliminium derived from 3b is useful in coupling reactions with silyl enol ethers, obtained from various β-ketoesters, ketones, and β-diketones, and high stereoselectivity with respect to the lactam ring was obtained for the more sterically demanding nucleophiles.…”

Section: Resultssupporting

confidence: 88%

Intermolecular and Intramolecular α-Amidoalkylation Reactions Using Bismuth Triflate as the Catalyst

Comesse

Garrigues

et al. 2007

J. Org. Chem.

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Bismuth(III) triflate was found to promote the formation of stable cyclic N-acyliminium species in remarkable catalytic amounts (1 mol %). The alpha-amidoalkylation process seems to be effective in intermolecular and intramolecular manners leading to alpha-substituted lactams and heterocyclic systems containing azacycles, respectively. By comparing our results with those obtained with the classical Lewis acids as catalysts, it was evidenced clearly that the use of bismuth(III) triflate had been efficient for nearly all alpha-acetoxy lactams we used, except for N-acyliminium precursors bearing a sulfur atom. Also, the process seems to be easy, general, and clean, having diastereoselectivity comparable to protocols using classical Lewis acids and resulting in the formation of polyheterocyclic systems in good to excellent yields (64-99% in acetonitrile as solvent).

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Section: Resultssupporting

confidence: 88%

Intermolecular and Intramolecular α-Amidoalkylation Reactions Using Bismuth Triflate as the Catalyst

Comesse

Garrigues

et al. 2007

J. Org. Chem.

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“…was used in the intermolecular reaction between an acetoxypyrrolidinone and indole. [26] Depending on the structures of the substrates, different reactivities have been observed with variation of the natures of the acids used for the generation of the N-acyliminium intermediates. When the hydroxylactam 35 (Scheme 11, obtained from NaBH 4 reduction of the corresponding imide) was treated with TFA, the thiazine 36 was obtained in high yield.…”

Section: Intramolecular α-Amidoalkylation and Parham Cyclization -Intmentioning

confidence: 99%

Strategies Based on Aryllithium and N‐Acyliminium Ion Cyclizations for the Stereocontrolled Synthesis of Alkaloids and Related Systems

et al. 2011

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The intramolecular α-amidoalkylation reactions of aromatic and heteroaromatic ring systems constitute a versatile approach for the synthesis of nitrogen heterocyles in a diastereoselective or enantioselective fashion. On the other hand, the intramolecular reactions of aryllithium compounds have also been extensively used in the synthesis of carbocycles and heterocycles. The use of imides as internal electrophiles is particularly attractive because of the potential to introduce diverse functionality into the cyclized products by subjecting the resulting α-hydroxylactams to intermolecular IntroductionAryllithium compounds and N-acyliminium ions are extremely versatile intermediates for the formation of carboncarbon bonds in organic synthesis. Cyclization of aryllithium compounds generated by halogen/lithium exchange with internal electrophiles (Parham cyclization) has become a valuable protocol for the stereoselective construction of carbocyclic and heterocyclic systems.[1] Many electrophiles remain inert during halogen/metal exchange reaction at low temperature, but are reactive enough to participate in a subsequent cyclization reaction. Halides, epoxides, or alkenes [2] are thus among the different types of internal electrophiles used in the Parham cyclization. When the internal electrophile is a carboxylate derivative, this anionic cyclization could be considered an anionic Friedel-Crafts equivalent, with the advantage that it lacks the electronic requirements of the classical reaction. Although it is possible to use carboxylic acids [3] or esters, [4] carbamates have proven to be much more effective internal electrophiles in Parham cycliacylations.[5] Amides are also useful electrophiles in Parham cyclizations, and it has been reported that in some cases there is an influence of the natures of the substituents at the nitrogen atom on the course of the cyclization reaction. [6,7] [a] Departamento In connection with our interest in aromatic lithiation, we have developed an anionic cyclization approach directed towards the construction of the pyrrolo[1,2-b]isoquinolone core based on N-(o-halobenzyl)pyrrole-2-carboxamides, showing that Weinreb amides and morpholine amides function as excellent internal electrophiles.[8] This observation could be explained by assuming that halogen/lithium exchange could be favored by a complex-induced proximity effect (CIPE).[9] This concept has been invoked to explain other metal/metal, hydrogen/metal, or halogen/metal [10] exchange reactions. Lithium/halogen exchange would thus be favored first by coordination of the inducing organolithium compound with amide or carbamate groups, and then by stabilization of the resulting aryllithium compound. The better behavior of Weinreb and morpholine amides relative to N,N-diethyl amides could be attributed to the extra stabilization of the intermediate generated after cyclization through the formation of an internal chelate. The scope of these Parham-type cyclizations has been extended to the formation of seven-and eight-membered rings [8b] ...

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“…Andrade and co-workers reported the efficiency of NbCl 5 to promote the generation of an enantiopure N-acyliminium ion, derived from (S)-malic acid, and subsequent additions of carbon nucleophiles [6].…”

Section: Nucleophilic Additions To An Enantiopure Cyclic N-acyliminiumentioning

confidence: 99%

Recent Applications of Niobium Catalysts in Organic Synthesis

Rocha¹

2006

MROC

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Niobium catalysts generally possess a good Lewis acidity and have received increased attention in recent years. The applications of niobium pentachloride as Lewis acid in organic synthesis have been recently reviewed. Since then, there has been an increasing number of examples on the use of niobium catalysts in organic reactions such as Biginelli reactions, Friedel-Crafts acylation and Sakurai-Hosomi reactions of acetals, Knoevenagel condensation, acetylation of alcohols and phenols, among others. Also, chiral niobium complexes have been reported to give high enantiomeric excesses in asymmetric Mannich-type reactions.In this review, recent applications of these versatile reagents in organic synthesis, including our own results, will be disclosed.

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Studies on the niobium pentachloride-mediated nucleophilic additions to an enantiopure cyclic N-acyliminium ion derived from (S)-malic acid

Cited by 4 publications

References 7 publications

Intermolecular and Intramolecular α-Amidoalkylation Reactions Using Bismuth Triflate as the Catalyst

Intermolecular and Intramolecular α-Amidoalkylation Reactions Using Bismuth Triflate as the Catalyst

Strategies Based on Aryllithium and N‐Acyliminium Ion Cyclizations for the Stereocontrolled Synthesis of Alkaloids and Related Systems

Recent Applications of Niobium Catalysts in Organic Synthesis

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