Intramolecular Cycloaddition of Geminal Dichloroazomethine Ylides to Multiple Carbon-Carbon Bonds

Geminal dichloroazomethine ylides generated by reaction of dichlorocarbene with Schiff bases derived from O-alkenyl- or O-alkynylsalicylaldehyde undergo intramolecular [3 + 2]-cycloaddition with participation of the olefinic or acetylenic dipolarophile to afford chromeno[4,3-b]pyrrole and chromeno[4,3-b]pyridine derivatives. The greatest yields of the intramolecular cycloaddition products were obtained from N-methyl-substituted dichloroazomethine ylides, whereas the main stabilization path of N-phenyl and N-tert-butyl derivatives was cyclization to geminal dichloroaziridines.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 4, 2005, pp. 571–577.Original Russian Text Copyright © 2005 by Khlebnikov, Voznyi, Novikov, Kostikov.     

Highly Selective Copper‐Catalyzed Asymmetric [3+2] Cycloaddition of Azomethine Ylides with Acyclic 1,3‐Dienes

The first examples of the catalytic asymmetric 1,3‐dipolar cycloaddition of azomethine ylides with acyclic activated 1,3‐dienes (and 1,3‐enynes) are described. Under copper catalysis, a selective cycloaddition at the terminal γ,δ‐C?C bond is observed. In addition, depending on the ligand used, either the exo or the endo adduct can be obtained with high selectivity. Under appropriate reaction conditions, the acyclic 1,6‐addition product is detected, suggesting a stepwise mechanism. The resulting C4‐alkenyl‐substituted pyrrolidines are suitable substrates for further access to polycyclic systems, as highlighted by the preparation of hexahydrochromeno[4,3‐b]pyrrole and the tetracyclic core of the alkaloid gracilamine.     

Diastereoselective Synthesis of Novel Pyrrolidine or Pyrrolizine‐Fused Benzo‐δ‐sultams via 1,3‐Dipolar Cycloadditions

The synthesis of novel pyrrolidine or pyrrolizine‐fused benzosultams is described. A number of (E)‐N‐(2‐formylphenyl)‐N‐alkyl‐2‐phenylethenesulfonamides derivatives were synthesized and subjected to intramolecular [3 + 2] cycloaddition with azomethine ylides derived in situ from the reaction with sarcosine, phenylglycine, and L‐proline.     

Intramolecular 1,3-Dipolar Cycloaddition of Geminal Difluoro Azomethine Ylides at Multiple Carbon-Carbon Bonds

N-Alkyl- and N-arylimines derived from o-allyl-, o-allyloxy-, and o-(2-propynyloxy)arenecarbaldehydes react with difluorocarbene to give indeno[1,2-b]pyrrole and chromeno[4,3-b]pyrrole derivatives. The reaction involves intermediate formation of difluoro-substituted azomethine ylides which undergo regio- and stereoselective intramolecular ring closure at the multiple bond.__________Translated from Zhurnal Organicheskoi Khimii, Vol. 41, No. 3, 2005, pp. 372–380.Original Russian Text Copyright © 2005 by Novikov, Khlebnikov, Voznyi, Besedina, Kostikov.Dedicated to Full Member of the Russian Academy of Sciences V.I. Minkin on his 70th Anniversary     

An Easy Access to the Synthesis of Sugar‐Based N‐Methyl‐Pyrrolidine via [3 + 2] Cycloaddition Methodology

Sugar‐based N‐methyl‐pyrrolidine derivatives have been synthesized by the cycloaddition reaction of the ylide generated from sarcosine and paraformaldehyde with the sugar‐derived dipolarophile. All the newly synthesized products were characterized by NMR (¹H, ¹³C), mass spectroscopy and elemental analysis.     

One pot,three component synthesis of spiroindenoquinoxaline pyrrolidine fused nitrochromene derivatives following 1,3-dipolar cycloaddition

An expedient one-pot sequential three-component synthesis of a series of diverse spiroindenoquinoxaline pyrrolidine fused nitrochromene derivatives following 1,3-dipolar cycloaddition of azomethine ylides generated in situ by the condensation of indenoquinoxalone and α-amino acids (L-proline and L-phenyl alanine) with 3-nitrochromenes as dipolarophile under classical as well as microwave irradiation is described. The protocol provides a mild reaction condition, high yield of the products, high regioselectivity, and operational simplicity to assemble complex structural entity in a single operation with good to excellent yield. The regio and stereochemical outcome of the cycloaddition reaction is ascertained by spectroscopic and single crystal X-ray analysis.     

Regio- and stereoselectivity of 1,3-dipolar cycloaddition of cyclic aldonitrones of the 3-imidazoline 3-oxide series to monosubstituted alkenes

Regio- and stereoselectivity of 1,3-dipolar cycloaddition of cyclic aldonitrones of the 3-imidazoline 3-oxide series mainly depends on the type of the substituent in the dipolarophile. The configuration of the main cycloadduct has been determined, and a method has been suggested to establish the stereochemistry of the cycloaddition products by¹H NMR spectroscopy. An increase in electron-acceptor properties of the substituent in the alkene molecule results in a decrease in the regio- and stereoselectivity of the cycloaddition.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 894–898, May, 1994.     

Thermal transformations of alk-1-enyl-N-phthalimidoaziridines

Thermolysis of alk-1-enyl-N-phthalimidoaziridines leads to products of 1,5-electrocyclization of intermediate azomethine ylides with participation of C=C bonds. If acyl or alkoxycarbonyl substituent is present in the aziridine ring, the C=O bond is also involved. Thermolysis of the title compounds in the presence of N-phenylmaleimide or dimethyl acetylenedicarboxylate under analogous conditions gives products of 1,3-dipolar cycloaddition of azomethine ylides to the double or triple bond of the dipolarophile.     

Microwave-assisted solvent-free intramolecular 1,3-dipolar cycloaddition reactions leading to hexahydrochromeno[4,3-b]pyrroles: scope and limitations

We report the microwave-assisted solvent-free synthesis of hexahydrochromeno[4,3-b]pyrroles. Intramolecular 1,3-dipolar cycloadditions proceed under these conditions within 15-40 min in 16-84% yields. An influence of the microwave irradiation upon various [3+2] cycloaddition reaction intermediates was studied. Additionally, a scope and limitations of these reactions including an influence of the dipolarophile geometry upon the cycloaddition selectivity and steric demands of the dipole upon its reactivity were also disclosed. These observations led us to postulate a preferable transition state of the reaction. Finally, an influence of the microwave irradiation to the isomerization of activated olefins was also described.     

KF/Al2O3 mediated 1,3-dipolar cycloaddition of azomethine ylides: a novel and convenient procedure for the synthesis of highly substituted pyrrolidines

The regio- and diastereoselective synthesis of pyrrolidine derivatives through 1,3-dipolar cycloaddition of an azomethine ylide and dipolarophile mediated by KF/Al₂O₃, a versatile solid supported reagent, is reported. KF/Al₂O₃ is sufficiently basic such that it can deprotonate α-imino esters to generate azomethine ylides and it also functions as a solid supported catalyst leading to the cycloadduct rather than the Michael adduct.     

1,3-Dipolar cycloadditions with azomethine ylide species generated from aminocyclopropanes

Two types of bicyclic N-cyclopropyl glycine ester derivatives have been prepared and put under scrutiny as possible precursors of azomethine ylides. The results demonstrate that they can indeed participate in 1,3-dipolar cycloaddition reactions with dipolarophiles, as illustrated in the cases of phenyl vinyl sulfone, N-phenylmaleimide, diethyl fumarate and diethyl maleate. The relative configurations of the major diastereoisomers produced are consistent with the predicted generation of azomethine ylide species, reacting in concerted cycloaddition processes. This unprecedented way of generating such 1,3-dipoles provides access to functionalised pyrrolizidine and pyrrolidine derivatives, that would be difficult to make directly by more classic methods. It was also found that using phenyl vinyl sulfone or N-phenylmaleimide as the dipolarophile reactant, a domino nucleophilic conjugate addition/1,3-dipolar cycloaddition process may operate competitively.     

A facile synthesis of novel dispiroheterocycles through solvent-free microwave-assisted [3+2] cycloaddition of azomethine ylides

A comparative study of the synthesis of novel dispiro pyrrolo/pyrrolizidino ring systems by the cycloaddition of azomethine ylides generated by a decarboxylative route from sarcosine/proline and isatin with the dipolarophile 9-arylidine-fluorene using four different methodologies is described. A solvent-free microwave-assisted approach gave products with the highest yields in a short time. Additionally, our solvent-free approach allowed the use of 4-N,N-dimethylaminobenzaldehyde, which failed to yield the desired cycloadducts under conventional approaches.     

A facile synthesis of chromeno[4,3-b]pyrroles derived from allyl derivatives of Baylis-Hillman adducts through intramolecular 1,3-dipolar cycloaddition using ultrasonication

Synthesis of a series of chromene[4,3-b]pyrroles has been accomplished through an intramolecular 1,3-dipolar cycloaddition reaction of an azomethine ylide with the dipolarophile derived from Baylis-Hillman adducts. Improved yields of the same products were obtained when the reaction was carried out under ultrasonication.     

Intramolecular thermal transformations of N-phthalimidoaziridines: 1,3-dipolar cyclo-addition and rearrangements*

The intramolecular thermal cycloaddition of N-phthalimidoaziridines at multiple bonds of substituents with the intermediate formation of azomethine ylides leads to condensed pyrrole derivatives, in which the five-membered ring is adjacent to a five-, six-, or seven-membered ring. Rearrangements, which sometimes become the predominant reactions, compete with cycloaddition. Thus, aziridines with aryl substituents readily isomerize to give imines with a 1,2-shift of the phthalimide group to one of the carbon atoms. Aziridines with one electron-withdrawing substituent probably do not open to give 1,3-dipoles but rather undergo a Cope-type rearrangement involving the three-membered ring and C = O bond of the second substituent. Even in intramolecular reactions, very low activity is found for the cyano group triple bond and aromatic ring bonds as dipolarophiles.     

Tandem cyclization-cycloaddition behavior of rhodium carbenoids with carbonyl compounds: stereoselective studies on the construction of novel epoxy-bridged tetrahydropyranone frameworks

Investigations and stereoselective studies on the tandem reactions of carbonyl ylides generated from alpha-diazo ketones in the presence of carbonyl compounds are presented in this paper. Intramolecular cyclization of rhodium carbenoids generated the transient five- or six-membered-ring carbonyl ylide dipoles, which efficiently underwent 1,3-dipolar cycloaddition reactions with various dipolarophiles such as aromatic aldehydes 15, alpha,beta-unsaturated aldehydes 18/24, alpha,beta-unsaturated ketones 27/28/31, and dienone 34. The transient carbonyl ylides underwent cycloadditions with various aromatic aldehydes to furnish diverse epoxy-bridged tetrahydropyranone ring systems in a diastereoselective manner. The cycloaddition of carbonyl ylides with alpha,beta-unsaturated aldehydes 18/24 or dienone 34 afforded C=O addition products in a chemoselective manner despite the presence of C=C bonds in the above dipolarophiles. Alternatively, the cycloaddition of carbonyl ylides with alpha,beta-unsaturated ketones 27/28 provided both the C=O and C=C cycloaddition products. The cycloaddition of carbonyl ylides with carbonyl compounds occurred in good yields and was found to be highly regio- and stereoselective. Single-crystal X-ray analyses were performed to unambiguously establish the structure and stereochemistry of the novel epoxy-bridged tetrahydropyranone ring systems 35a/38. Compound 35a exhibited both intermolecular C-H...O and intramolecular C-H...pi interaction motifs in the solid-state architecture. The regio-, chemo-, and stereoselectivity observed in these reactions have been investigated by semiempirical AM1 MO calculations. FMO analyses and transition state calculations have been performed for the cycloaddition of carbonyl ylides with alpha,beta-unsaturated carbonyl compounds such as tetracyclone (34) and cyclopentenone (27a). Both FMO and transition state calculations correctly predicted the regio- and stereochemistry of the cycloadducts. The calculations further revealed that a severe steric interaction caused by the phenyl rings present in dipolarophile 34 with dipole 14a increases the activation barrier of the transition state during the cycloaddition process.     

1,3-Dipolar Cycloaddition of Azomethine Ylides Generated from Schiff Bases and Difluorocarbene to Symmetric Olefins

Difluoro(iminio)methanides generated by the action of difluorocarbene on Schiff bases react with derivatives of maleic and fumaric acids, following the 1,3-dipolar cycloaddition pattern to give 2,2-difluoropyrrolidines which were detected by gas chromatography-mass spectrometry. The final products are stereo-isomeric substituted 2-pyrrolidinones formed by hydrolysis of difluoropyrrolidines and their dehydrofluorination products, 2-fluoro-4,5-dihydropyrroles. The observed stereoselectivity of the cycloaddition suggests Z configuration of intermediate ylide and both endo- and exo-approach to the dipolarophile in the transition state corresponding to cycloaddition.     

New pyrrolidine and pyrroline derivatives of fullerenes: from the synthesis to the use in light-converting systems

The results of the authors’ studies on the [2+3] cycloaddition of azomethine and nitrile ylides generated from picolylamine and benzylamine derivatives to fullerenes are systematized and new experimental data are considered. Catalysts and microwave radiation promoting the formation of ylides and their addition to fullerenes were successfully used for the first time. A large series of new pyrrolidine and pyrroline derivatives of fullerenes C₆₀ and C₇₀ were synthesized and characterized. The proposed procedures afford the reaction products in yields twice as high (80–85%) as those attained by the classical Prato reaction. The reactions proceed with virtually complete regio- (in the case of C₇₀) and stereoselectivity to afford only cis-2′,5′-disubstituted and trans-1′,2′,5′-trisubstituted pyrrolidinofullerenes. Pyridyl-substituted pyrrolidinofullerenes react with metalloporphyrins and phthalocyanines to form self-ordered coordination complexes. The latter are analogs of natural photosynthetic antenna systems due to photoinduced charge separation that occurs in these complexes upon exposure to light. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 873–898, May, 2008.     

[3+2] Cycloaddition of metal-containing azomethine ylides for highly efficient synthesis of mitosene skeleton

Efficient synthesis of tricyclic indole derivatives bearing a substituent at the 3-position of the indole nucleus was achieved by the [3+2] cycloaddition reaction of transition metal-containing azomethine ylides derived from N-(o-alkynylphenyl)imines with vinyl ethers. Third-row transition metal complexes, especially PtCl₂, turned out to be highly efficient for the reaction of internal alkynes and imidate substrates with wide generality. Moreover, as strong support for the reaction mechanism, the intermediate Pt-carbene complex was found to undergo intramolecular C-H bond insertion reaction to give tetracyclic indoline derivatives when benzyl vinyl ether was employed as a dipolarophile. This protocol provided a facile synthesis of highly functionalized tricyclic indole derivatives found as the basic skeleton of the mitosene family, such as mitomycin C.     

Intramolecular 1,3-cycloadditions of nitrile ylides bearing an acetylenic function

Treatment of amides 1a,b with thionyl chloride followed by reaction with triethylamine gave 1,4-dihydro[1]benzopyrano[4,3-b]pyrrole derivatives ( 4a,b ) arising from intramolecular 1,3-cycloaddition of intermediate nitrile ylides ( 3a,b ).     

Binaphthol-derived bisphosphoric acids serve as efficient organocatalysts for highly enantioselective 1,3-dipolar cycloaddition of azomethine ylides to electron-deficient olefins

A variety of chiral bisphosphoric acids derived from binaphthols have been evaluated for enantioselective 1,3-dipolar cycloaddition reactions, revealing that the feature of the linker in the catalysts exerted great impact on the stereoselectivity. Among them, the oxygen-linked bisphosphoric acid 1a provided the highest level of stereoselectivity for the 1,3-dipolar cycloaddition reaction tolerating a wide range of substrates including azomethine ylides, generated in situ from a broad scope of aldehydes and α-amino esters, and various electron-deficient dipolarophiles such as maleates, fumarates, vinyl ketones, and esters. This reaction actually represents one of the most enantioselective catalytic approaches to access structurally diverse pyrrolidines with excellent optical purity. Theoretical calculations with DFT method on the formation of azomethine ylides and on the transition states of the 1,3-dipolar cycloaddition step showed that the dipole and dipolarophile were simultaneously activated by the bifunctional chiral bisphosphoric acids through the formation of hydrogen bonds. The effect of the bisphosphoric acids on reactivity and stereochemistry of the three-component 1,3-dipolar cycloaddition reaction was also theoretically rationalized. The bisphosphoric acid catalyst 1a may take on a half-moon shape with the two phosphoric acid groups forming two intramolecular hydrogen bonds. In the case of maleates, one phosphate acts as a base to activate the 1,3-dipole, and simultaneously, the two hydroxyl groups in the catalyst 1a may respectively form two hydrogen bonds with the two ester groups of maleate to make it more electronically deficient as a much stronger dipolarophile to participate in a concerted 1,3-dipolar cycloaddition with azomethine ylide. However, in the cases involving acrylate and fumarate dipolarophiles, only one hydroxyl group forms a hydrogen bond with the ester functional group to lower the LUMO of the C-C double bond and another one is remained to adjust the acidity and basicity of two phosphoric acids to activate the dipole and dipolarophile more effectively.