Über die Reaktion von Pyrazolidon‐(3) mit Carbonylverbindungen

Dorn, Helmut; Otto, Albrecht

doi:10.1002/cber.19681010936

Cited by 141 publications

(26 citation statements)

References 20 publications

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“…10 A recent intramolecular process has been applied to the synthesis of androstenoarylpyrazolines 3 using BF 3 ·OEt 2 as Lewis acid, previously used for intermolecular cycloadditions (Scheme 2). 20 The reaction takes place stereoselectively at 0 °C in high yields from the corresponding hydrazones 1 by a BF 3 Three-component or consecutive intermolecular 1,3-DC of azomethine imines with α-oxoketenes 5 has been performed under thermal conditions. Both, hydrazones and dipolarophiles are generated in situ, affording the corresponding pyrazolidinones 6 in a stereoselective manner (Scheme 3).…”

Section: From Monosubstituted Hydrazinesmentioning

confidence: 99%

1,3-Dipolar cycloadditions of azomethine imines

2015

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Azomethine imines are considered 1,3-dipoles of the aza-allyl type which are transient intermediates and should be generated in situ but can also be stable and isolable compounds. They react with electron-rich and electron-poor olefins as well as with acetylenic compounds and allenoates mainly by a [3 + 2] cycloaddition but they can also take part in [3 + 3], [4 + 3], [3 + 2 + 2] and [5 + 3] with different dipolarophiles. These 1,3-dipolar cycloadditions (1,3-DC) can be performed not only under thermal or microwave conditions but also using metallo- and organocatalytic systems. In recent years enantiocatalyzed 1,3-dipolar cycloadditions have been extensively considered and applied to the synthesis of a great variety of dinitrogenated heterocycles with biological activity. Acyclic azomethine imines derived from mono and disubstituted hydrazones could be generated by prototropy under heating or by using Lewis or Brønsted acids to give, after [3 + 2] cycloadditions, pyrazolidines and pyrazolines. Cyclic azomethine imines, incorporating a C-N bond in a ring, such as isoquinolinium imides are the most widely used dipoles in normal and inverse-electron demand 1,3-DC allowing the synthesis of tetrahydro-, dihydro- and unsaturated pyrazolo[1,5-a]isoquinolines in racemic and enantioenriched forms with interesting biological activity. Pyridinium and quinolinium imides give the corresponding pyrazolopyridines and indazolo[3,2-a]isoquinolines, respectively. In the case of cyclic azomethine imines with an N-N bond incorporated into a ring, N-alkylidene-3-oxo-pyrazolidinium ylides are the most popular stable and isolated dipoles able to form dinitrogen-fused saturated and unsaturated pyrazolopyrazolones as racemic or enantiomerically enriched compounds present in many pharmaceuticals, agrochemicals and other useful chemicals.

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Section: From Monosubstituted Hydrazinesmentioning

confidence: 99%

1,3-Dipolar cycloadditions of azomethine imines

2015

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“…Their potential application as dipoles in cycloadditions with alkenes or alkynes has been established a long time ago. [8] Several pyrazolidin-3-one derivatives exhibit biological activities, and the importance of this type of compounds has risen significantly in the last two decades. One of the examples is the cycloaddition product LY 186826, which exhibits high anti-bacterial activity.…”

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confidence: 99%

Organocatalytic and Stereoselective [3 + 2] Cycloadditions of Azomethine Imines with α,β‐Unsaturated Aldehydes

et al. 2006

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Bipyrazolidin-3-one derivatives are biologically significant compounds and their importance has increased in the past decades. In this paper, the first stereoselective [3 + 2] dipolar cycloadditions of azomethine imines with a,b-unsaturated aldehydes catalyzed by readily available a,adiarylprolinol salts are reported, providing a facile route to the synthesis of various chiral bipyrazolidin-3-one derivatives under mild conditions. The organocatalyst 1 g with strongly electron-withdrawing groups exhibited the best stereoselectivity (exo:endo up to 98:2, for exo product up to 97 % ee), in the combination with trifluoroacetic acid.Keywords: azomethine imines; bipyrazolidin-3-one; diarylprolinols; dipolar cycloaddition; organocatalysis; unsaturated aldehydes Recently, small organic molecules-catalyzed enantioselective transformations have attracted increasing attention.[1] Particularly, asymmetric amine catalysis has been the subject of intensive research since the discovery of the proline-catalyzed direct asymmetric intermolecular aldol reaction. Numerous 1,2-or 1,4-addition reactions with excellent enantioselectivities have been reported in the last five years.[2] On the other hand, asymmetric cycloaddition reactions have also been actively explored in the amine catalysis. The generation of active iminium ions, which are thought to lower the energy of the dienophile LUMO, generally plays a key role in the successful cycloaddition reactions. Nevertheless, the current examples are mostly limited to the common DielsAlder reactions.[3]The catalytic asymmetric [3 + 2] dipolar cycloaddition reaction provides one of the most powerful strategies for the enantioselective construction of fivemembered heterocycles. While considerable progress has been made in the metal-catalyzed asymmetric synthesis over the past decades, [4] the application of chiral organocatalysts in [3 + 2] cycloaddition reactions remains in its infancy since MacMillan's pioneering works in 2000.[5] Furthermore, only nitrones have been tested as the successful dipoles to date.[6] Based on our successful experience on the asymmetric vinylogous Michael addition of a,a-dicyanoolefins to a,bunsaturated aldehydes catalyzed by chiral a,a-diarylprolinol salts, [7] here we present the first asymmetric [3 + 2] cycloaddition reaction of azomethine imines with a,b-unsaturated aldehydes.Azomethine imines such as 2, prepared by the condensation of pyrazolidin-3-one with aldehydes, are stable and easily handled compounds. Their potential application as dipoles in cycloadditions with alkenes or alkynes has been established a long time ago. [8] Several pyrazolidin-3-one derivatives exhibit biological activities, and the importance of this type of compounds has risen significantly in the last two decades. One of the examples is the cycloaddition product LY 186826, which exhibits high anti-bacterial activity. [9] On the other hand, although a variety of asymmetric cycloadditions of chiral azomethine imines have been reported, [10] the catalytic enantioselective [...

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“…2 Although asymmetric hetero Diels-Alder 3 or 1,3-dipolar cycloadditions with azomethine ylids 4 are now well known methods for the synthesis of piperidine or pyrrolidine derivatives, very little work is known on the azomethine imine series. Since the pioneering works of Dorn 5 and Oppolzer in this field, 6 it was known that azomethine imines could react with several dipolarophiles, leading to polysubstituted pyrazolidines. 7 Some recent important results were also reported by 8 showing that in the racemic series, good control of relative configurations could be obtained with this reaction.…”

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Diastereoselective Cycloadditions of Chiral Non-racemic Azomethine Imines

et al. 2000

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3,4]oxadiazinan-2-one (6) is an easily available building block and acts as a chiral non-racemic precursor for azomethine imines. The ylid can be formed regioselectively with various aldehydes and reacts in an efficient manner with a wide range of dipolarophiles. The regio-and diastereoselectivity of the cycloadditions have been fully investigated and can lead, in the best cases, to the creation of three contiguous asymmetric centers in a single step, with complete control of relative and absolute configurations.

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Über die Reaktion von Pyrazolidon‐(3) mit Carbonylverbindungen

Cited by 141 publications

References 20 publications

1,3-Dipolar cycloadditions of azomethine imines

1,3-Dipolar cycloadditions of azomethine imines

Organocatalytic and Stereoselective [3 + 2] Cycloadditions of Azomethine Imines with α,β‐Unsaturated Aldehydes

Diastereoselective Cycloadditions of Chiral Non-racemic Azomethine Imines

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