Nonstabilized Azomethine Ylides Research Articles

Stereospecific Route to 5,11-Methanomorphanthridine Alkaloids via Intramolecular 1,3-Dipolar Cycloaddition of Nonstabilized Azomethine Ylide: Formal Total Synthesis of (±)-Pancracine

The core structure of the complex pentacyclic 5,11-methanomorphanthridine alkaloids is constructed stereospecifically in one step employing an intramolecular [3 + 2]-cycloaddition of nonstabilized azomethine ylide as the key step. The strategy is demonstrated by accomplishing the formal total synthesis of (+/-)-pancracine. [reaction: see text]

A facile entry into a novel class of dispiroheterocycles through 1,3-dipolar cycloaddition

The cycloaddition reaction of non-stabilized azomethine ylides, generated through decarboxylation and deprotonation, with (E)-2-arylidene-1-tetralones as dipolarophile has been investigated. A high degree of regioselectivity has been observed in the synthesis of a new class of functionalised dispiroheterocyclic compounds bearing a tetralone, acenapthenequinone and oxindole framework.

A Three‐Component, One‐Pot Synthesis of Indolizidines and Related Heterocycles via the [3 + 2] Cycloaddition of Nonstabilized Azomethine Ylides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

1,3‐Dipolar Cycloaddition Reactions of Pyridinium Azomethine Ylides Containing 5,6‐Dicyanopyrazines.

AbstractFor Abstract see ChemInform Abstract in Full Text.

1,3-Dipolar cycloaddition of stabilised and non-stabilised azomethine ylides derived from uracil polyoxin C (UPoC): access to nikkomycin analogues

Cascade thermal and decarboxylative cycloaddition reactions of uracil polyoxin C (UPoC) with mono- and di-carbonyl compounds in the presence of a dipolarophile leads, via stabilised and non-stabilised azomethine ylides respectively, to a series of polyoxin cycloadducts related to Nikkomycin B in good to excellent yields and high diastereoselectivity.

A three-component, one-pot synthesis of indolizidines and related heterocycles via the [3+2] cycloaddition of nonstabilized azomethine ylides.

Nonstabilized azomethine ylides (i.e. those bearing only hydrogens or alkyl groups) can be generated from (2-azaallyl)stannanes and (2-azaallyl)silanes through an intramolecular N-alkylation/demetalation cascade. The resulting ylides undergo [3+2] cycloaddition with electron-poor or electron-rich dipolarophiles yielding indolizidines and related 1-aza[m.3.0]bicycloalkane systems in good yield. An in situ protocol allows for a one-pot, three-component synthesis of indolizidines. The (2-azaallyl)stannanes tolerate enolizable hydrogens in these cycloadditions, while (2-azaallyl)silanes do not. The mechanism of the cycloaddition cascade is clarified by a series of control experiments. The same (2-azaallyl)stannanes may be transmetalated by n-butyllithium to generate 2-azaallyllithiums, which also may undergo a [3+2] cycloaddition/N-alkylation cascade to form indolizidines.

1,3-Dipolar Cycloaddition Reactions of Pyridinium Azomethine Ylides Containing 5,6-Dicyanopyrazines

The intermolecular 1,3-dipolar cycloaddition reaction of azomethine ylides with carbon-carbon double or triple bonds represents an efficient and convergent method for the construction of heterocyclic structures containing a single nitrogen atom. 1 One of the most frequently employed methods for the generation of azomethine ylide involves the thermolysis of an aziridine. 2 However, the ring opening of aziridines to azomethine ylides is limited to those having substituent groups capable of stabilizing the dipole centers. Desilylation of α-trimethylsilylonium salts represents another convenient method of generating azomethine ylide. 3 More recently it has been found that nonstabilized azomethine ylides can be generated by the deprotonation of amine Noxides. 4 Azomethine ylides are too unstable to be isolated, and are typically used in situ. Of the various types of azomethine ylides, the pyridinium azomethine ylides are among the most attractive synthetically because they are easily prepared from the appropriate N-alkylpyridinium salt with base and their cycloadducts, the indolizines, have been used as synthetic building blocks. 5 In our continuing efforts to develop functional dyes based on dicyanopyrazine chromophores, we have become interested in pyridinium azomethine ylides containing dicyanopyrazines and their 1,3-dipolar cycloaddition reaction with dipolarophiles, because the indolizine cycloadducts, containing dicyanopyrazines, might meet our purpose. Dyes and pigments generally possess satisfactory color, and good color fastness properties against light and heat, and additional properties such as near infrared absorption, pleochroism, and photoconductivity. 6 The majority of these properties are caused by intramolecular charge-transfer interactions involving π-electrons and intermolecular π-π interactions of the dye chromophores. 7 In this paper, we report the generation of pyridinium azomethine ylide intermediates and the results of 1,3-dipolar cycloaddition reactions of the ylides with dipolarophiles to provide indolizines containing 5,6-dicyanopyrazine. The preparation of methyl or phenyl substituted 2-bromomethyl5,6-dicyanopyrazine 1 is described in a previous report. 6b

Cycloadditions of Nonstabilized 2‐Azaallyllithiums (2‐Azaallyl Anions) and Azomethine Ylides with Alkenes: [3 + 2] Approaches to Pyrrolidines and Application to Alkaloid Total Synthesis.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Flavindogenides as 2π Component in 1,3‐Dipolar Cycloaddition Reaction — An Efficient Synthesis of New Class of Dispiroheterocycles.

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Alkaloid Synthesis via [3 + 2] Cycloadditions

AbstractFor Abstract see ChemInform Abstract in Full Text.

A Convenient Synthesis of Pyrrolo[3,4-c]quinolines

A new route to the pyrrolo[3,4-c]quinoline ring system has been developed. The synthesis proceeds stereoselectively in three steps, using 1,3-dipolar cycloaddition of azomethine ylides as a key step. First, a series of 4-arylpyrrolidine-3-carboxylic acids have been prepared from the appropriate cinnamic esters and a nonstabilized azomethine ylide. The reduction of a nitro group on the aromatic ring was followed by acid-catalyzed intramolecular lactam formation.

Cycloadditions of Nonstabilized2-Azaallyllithiums (2-Azaallyl Anions) and Azomethine Ylides withAlkenes: [3+2] Approaches to Pyrrolidinesand Application to Alkaloid Total Synthesis

The [3+2] cycloaddition of 2-azaallyl anions with al­kenes represents an attractive strategy for the synthesis of substituted pyrrolidines. Although cycloadditions of 2-azaallyl anions stabilized by aryl and ester groups have been known for more than three decades, only recently have versions bearing simply hydrogen or alkyl groups been discovered. These nonstabilized 2-azaallyl anions are generated by the low temperature transmetalation of (2-azaallyl)stannanes with alkyllithiums. The resulting nonstabilized 2-azaallyllithiums undergo cycloaddition with certain alkenes and alkynes in both intra- and intermolecular modes to yield pyrrolidine or pyrroline cycloadducts. The methodology has been extended to 2-azapentadienyllithiums, heteroatom-substituted 2-azaallyllithiums, and polymer-supported 2-azaallyllithiums. Asymmetric 2-azaallyl anion cycloadditions have also been investigated. Nonstabilized azomethine ylides may also be generated from (2-azaallyl)stannanes via an N-alkylation/destannylation or N-protonation/destannylation sequence. Together, the cycloaddition of nonstabilized 2-azaallyllithiums and azomethine ylides with alkenes allows access to a broader range of pyrrolidines, since these species have complimentary reactivity profiles.

1,3‐Dipolar Cycloaddition Reactions of 3′,5′‐Bis‐O‐silyl Thymidines. Synthesis of Novel Azabicyclic Compounds.

AbstractFor Abstract see ChemInform Abstract in Full Text.

THE CONVENIENT SYNTHESIS OF 3-ALKYLOXYCARBONYLPYRROLIDINE DERIVATIVES

ABSTRACT A series of 3-alkyloxycarbonylpyrrolidine derivatives are readily achieved via 1,3-dipolar cycloaddition of α,β-unsaturated esters with nonstabilized azomethine ylides in the presence of samarium diiodide.

Alkaloid synthesis via [3+2] cycloadditions

Abstract Tin-lithium exchange on (2-azaallyl)stannanes affords nonstabilized 2-azaallyllithiums (2-azaallyl anions) that undergo [π4s+π2s] cycloadditions with alkenes to afford pyrrolidines. The scope of this method has been expanded to include 2-azapentadienyllithiums and heteroatom-substituted 2-azaallyllithiums. Alternatively, the (2-azaallyl)stannanes may also be used to generate nonstabilized azomethine ylides via N-alkylation/destannylation or N-protonation/destannylation, and these ylides were also found to be useful for the synthesis of pyrrolidines by [π4s+π2s] cycloadditions with alkenes. Applications of both methods to the total synthesis of alkaloids such as (+)-coccinine, lepadiformine stereoisomers, lapidilectine B, and indolizidine 239CD have been accomplished.

1,3-DIPOLAR CYCLOADDITION REACTIONS OF 3′,5′-BIS-O-SILYL THYMIDINES. SYNTHESIS OF NOVEL AZABICYCLIC COMPOUNDS

ABSTRACT An efficient one step procedure for the preparation of (4.3.0) bicyclic N-methylpyrrolidine thymidine derivatives 4, using cycloaddition reaction of the highly reactive non-stabilized azomethine ylide [Y] with 3′,5′-Bis-O-silylthymidines 3.

FLAVINDOGENIDES AS 2π COMPONENT IN 1,3-DIPOLAR CYCLOADDITION REACTION—AN EFFICIENT SYNTHESIS OF NEW CLASS OF DISPIROHETEROCYCLES

ABSTRACT The cycloaddition reaction of non-stabilised azomethine ylides towards (E) 3-arylidene flavan-4-ones or flavindogenides as new dipolarophile have been investigated. High degree of regio and stereoselectivity has been observed in the synthesis of unique class of densely functionalised dispiroheterocyclic compounds bearing flavan-4-one frameworks.

3+2]-Cycloaddition of nonstabilized azomethine ylides, part 9: A general approach for the construction of X-azabicyclo[m.2.1]alkanes in optically pure form by asymmetric 1,3-dipolar cycloaddition reactions

A general strategy for the construction of X-azabicyclo[m.2.1]alkane frameworks in optically pure form is reported by the asymmetric [3+2]-cycloaddition reaction of cyclic azomethine ylides with Oppolzer's acryloyl camphor sultam.

The Synthesis of Substituted Pyrrolidines and 2,5-Dihydropyrroles via 1,3-Dipolar Cycloaddition of Nonstabilized Azomethine Ylides

The Synthesis of Substituted Pyrrolidines and 2,5-Dihydropyrroles <i>via</i> 1,3-Dipolar Cycloaddition of Nonstabilized Azomethine Ylides

ChemInform Abstract: [3 + 2] Cycloaddition of Nonstabilized Azomethine Ylides. Part 7. Stereoselective Synthesis of Epibatidine and Analogues.

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