Potassium carbonate-promoted stereospecific 5-endo-trig cyclization of unactivated allenes in the absence of any transition metals

[STRUCTURE: SEE TEXT] Formation of 3-pyrrolines from simple unactivated allenes bearing a protected amino group under basic conditions is described. Treatment of alpha-amino allenes with potassium carbonate in DMF under reflux in the absence of any transition-metal catalysts gave the corresponding 3-pyrrolines in good to excellent yields, by 5-endo-trig mode cycloisomerization. The reaction of internal allenes with an axial chirality afforded the corresponding 3-pyrrolines in a stereoselective manner.     

Regio- and stereo-selective synthesis of multi-substituted 3-pyrrolines

A regio-and stereo-selective synthesis of multi-substituted 3-pyrrolines has been developed.The multi-substituted 3-pyrrolines were synthesized in good yields by 1,3-dipolar cycloaddition of methyl 2-(phenylselanyl)acrylate with azomethine ylides,followed by N-acylation and oxidation-elimination of phenylseleno group.     

Synthesis of 2-(3-hydroxy-2-methyl-1-alkenyl)-1-pyrrolines and 2-(3-hydroxybutyl)-1-pyrroline using α-lithiated 2-methyl-1-pyrroline

Condensation of 2-methyl-1-pyrroline with chloroacetone or 3-chloro-2-butanone using LDA in THF afforded novel 2-(3-hydroxy-2-methyl-1-alkenyl)-1-pyrrolines via a peculiar reaction mechanism instead of the anticipated 2-(3-oxobutyl)-1-pyrrolines. The intermediacy of 2-(2,3-epoxy-2-methylalkyl)-1-pyrrolines in the latter transformation was demonstrated by immediate reductive epoxide ring opening utilizing lithium aluminium hydride in diethyl ether. Furthermore, 2-(3-oxobutyl)-1-pyrroline was prepared via an alternative approach through alkylation of 2-methyl-1-pyrroline with 3-chloro-2-(methoxymethyloxy)-1-propene using LDA in THF, followed by acid hydrolysis. Reduction of 2-(3-oxobutyl)-1-pyrroline by sodium borohydride in methanol afforded the corresponding 2-(3-hydroxybutyl)-1-pyrroline in good yield.     

Réaction de l'azaallyllithium en série acétylénique: Une méthode directe de préparation de phényléthynyl pyrrolidines, -pyrrolines et -pyrroles N-non substitués et N-alkylés

Cycloaddition of 1,3-diphenyl-2-azaallyllithium to tolane, diphenylbutadiyne and 1,4-diphenylbutenyne E produces quantitatively 2,3,4,5-tetraphenylpyrrole, 3-phenylethynyl-2,4,5-triphenyl-3-pyrroline and 3-phenylethynyl-2,4,5-triphenylpyrrolidine, respectively. Treatment before hydrolysis with benzyl bromide or dimethl sulfide gives N-alkyl-substituted derivatives. The structure of 3-pyrrolines was established by spectral data and chemical correlations. Stereochemical courses of this new synthetic method for 3-pyrrolines are discussed.     

Über die Synthese von substituierten 2-Amino-1-pyrrolinen, 1. Mitt.

Three methods for the synthesis of various substituted 2-amino-1-pyrrolines are described:

1. Cyclization of 2.2-disubstituted 4-bromobutyronitriles with ammonia to yield 3.3-disubstituted 2-amino-1-pyrrolines.
2. Reduction of 2-aminopyrrolin-5-ones or 2-iminosuccinimides with LiAlH₄, a route leading especially to 3.3.4-substituted 2-aminopyrrolines.
3. Chlorination of 4.4-disubstituted pyrrolidones with POCl₃ followed by treatment with NH₃ gives 4.4-disubstituted 2-amino-1-pyrrolines.

     

Nucleophilic phosphine-catalyzed [3+2] cycloaddition of allenes with N-(thio)phosphoryl imines and acidic methanolysis of adducts N-(thio)phosphoryl 3-pyrrolines: a facile synthesis of free amine 3-pyrrolines

In this report, the dipolarophile imines with easily removable activating group O,O-diethyl(thio)phosphoryl have been investigated in the nucleophilic phosphine-catalyzed [3+2] cycloaddition reaction of electron-deficient allenes. Under the catalysis of a tertiary phosphine, N-(thio)phosphorylimines readily undergo the [3+2] cycloaddition reaction with ethyl 2,3-butadienoate or ethyl 2,3-pentadienoate, affording the corresponding N-(thio)phosphoryl 3-pyrrolines in moderate to high yields with good diastereoselectivity. Removal of the (thio)phosphoryl group from the adducts has been successfully achieved via the acidic methanolysis of the P-N bond, giving the free amine 3-pyrrolines in fair to good yields without severe aromatization. Thus, a facile synthesis of N-unsubstituted 3-pyrrolines is established from the phosphine-catalyzed [3+2] cycloaddition reaction of allenes with imines.     

Short and efficient synthesis of 2H-pyrroles from 7-oxanorbornadiene derivatives

A microwave-assisted tandem [3+2] cycloaddition/retro-Diels-Alder reaction of azomethine ylides derived from imines of α-amino esters to dimethyl 7-oxabicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate derivatives is described. The procedure delivers, in a short reaction time, pyrrolines in high yields. In a such sequence, the oxanorbornadiene derivatives behave as masked forms of dimethyl acetylenedicarboxylate. Subsequent oxidation of the synthesized 3-pyrrolines with DDQ affords 2H-pyrroles with yields in the 76-88% range. If this three-step sequence is run on the non-substituted 7-oxabicycloheptadienedicarboxylate, purification of the intermediate 3-pyrrolines is avoided to afford 2H-pyrroles in less than 2 h.     

Synthesis of 2-Arylpyrrolidines by Reactions of 3-Arylidene-1-pyrrolines with Phenols

Russian Journal of General Chemistry - The reaction of 3-arylidene-1-pyrrolines with phenols yielded 2-arylpyrrolidines. The proposed method makes it possible to obtain pyrrolidines containing a...     

The formation of Δ2-pyrrolines by base catalysed nitrile dimerisation

The reaction of (1-bromocyclohexyl)methylidenemalonitrile and 2-bromo-2-methylpropylidenemalonitrile with sodium methoxide in methanoi has been shown to give high yields of Δ²-pyrrolines in a Thorpe reaction involving two initially formed nitrile products. The by-products formed, (hexahydrobenzaldehyde dimethyl acetal]-1-malonitrile and 1,1-dicyano-2,2-dimethyl-3,3-dimethoxy propane, respectively, were shown to be the only products when the malonitriles were treated with pyridine in methanol. On the action of acid, the Δ²-pyrrolines aromatised to yield 1,2-dihydro-3H-pyrrolizineproducts. Structure det different reaction paths have been discussed.     

A Convenient Synthesis of 3-Nitro-2-pyrrolines: Regioselective Oxidations of Substituted Pyrrolidines to Pyrrolines+

A regiospecific oxidation of 3-nitro-4-substituted phenyl pyrrolidines with KMnO₄ to 3-nitro-4-substituted phenyl 2-pyrrolines and the hydroxymethylations of 3-nitro-4-substituted phenyl pyrrolidines have been described.     

Copper-catalyzed multicomponent reaction: facile access to functionalized 5-arylidene-2-imino-3-pyrrolines

The synthesis of a novel class of 2-imino-5-arylidene-3-pyrrolines via a copper-catalyzed multicomponent reaction of sulfonyl azides with alkynes and aziridines is described. The protocol is efficient and general.     

Highly diastereoselective synthesis of 1-pyrrolines via SnCl4-promoted [3 + 2] cycloaddition between activated donor-acceptor cyclopropanes and nitriles

Activated donor-acceptor cyclopropanes underwent formal [3 + 2] cycloaddition with nitriles in the presence of SnCl(4). The product 1-pyrrolines were isolated as single cis-diastereomers in moderate to good yields.     

Formation of novel 1,2,3,4-tetrasubstituted 3-pyrrolines via cyclisation of γ-halo-β-ketoesters with aromatic amines and aldehydes

Cyclisation of γ-halo-β-ketoesters with aromatic amines and aldehydes in methanol gave novel polysubstituted 3-pyrroline derivatives. A plausible mechanism for the reaction has been proposed. The structures of 1,2,3,4-tetrasubstituted 3-pyrrolines were confirmed by NMR spectroscopy and X-ray crystallography.     

Reaction of 3-(Arylmethylidene)-1-pyrrolines with Acetone. Synthesis of Norhygrine Derivatives

Russian Journal of Organic Chemistry - An efficient procedure has been developed for the synthesis of analogs of the alkaloid norhygrine by reaction of 3-(arylmethylidene)-1-pyrrolines with...     

Stereoselective synthesis of highly substituted Delta1-pyrrolines: exo-selective 1,3-dipolar cycloaddition reactions with azlactones

We report herein a silver(I)-catalyzed exo-selective synthesis of highly substituted Delta1-pyrroline scaffolds from amino acid-derived münchnones. Silver acetate successfully catalyzed the cycloaddition reaction of azlactones with alkenes, generating Delta1-pyrrolines in very good yields without isomerization to the Delta2-pyrrolines or decarboxylation.     

Effect of metal ions in organic synthesis : Part XXXIII. 2-hydroxy-4-pyrrolines as stable intermediates in the synthesis of 1-aminopyrrole derivatives

The reactions of conjugated aroylazoalkenes with β-diketones and β-ketoesters in the presence and in the absence of copper(II) chloride as catalyst have been studied. In the first case, 1-aminopyrrole derivatives have been obtained, while in the second case the formation of 2-hydroxy-4-pyrrolines as stable intermediates has been frequently detected. The observations on the conditions of the formation of either or both products, as well as the proof of the easy conversion of 2-hydroxy-4-pyrrolines into pyrrole derivatives elucidate the much debated behaviour of these reactions.     

Intramolecular azide-diene cycloadditions. An approach to fused bicyclic 3-pyrrolines based on a one-pot nitrene-diene cycloaddition equivalent.

Cyclization of heterosubstituted ω-azidodienes 11 provides fused bicyclic 3-pyrrolines 12 in one operation. These pyrrolines are potentially useful intermediates for natural products synthesis, as illustrated by further functionalization.     

13C chemical shifts of Δ1-pyrrolines

¹³C chemical shifts are reported for the ring carbons of several substituted Δ¹-pyrrolines. Average values for methine and methylene ring carbons facilitate structure elucidation of substituted δ¹-pyrrolines by ¹³C NMR spectroscopy.     

Reaction of alpha-(N-carbamoyl)alkylcuprates with enantioenriched propargyl electrophiles: synthesis of enantioenriched 3-pyrrolines

Enantioenriched propargyl mesylates or perfluorobenzoates react with alpha-(N-carbamoyl)alkylcuprates to afford scalemic alpha-(N-carbamoyl) allenes which undergo N-Boc deprotection and AgNO3-promoted cyclization to afford N-alkyl-3-pyrrolines. The synthetic sequence proceeds under optimal conditions with no loss of enantiopurity relative to the starting propargyl alcohols prepared by asymmetric addition of terminal alkynes to aldehydes.     

Synthesis of nitrogen-containing compounds using chromium Fischer carbene complexes

Synthetic utility of the Fischer-type carbene complexes of chromium for the preparation of nitrogen-containing compounds is demonstrated. Alkoxy carbene complexes reacted with imines to give (optically active) 3-pyrrolines and beta-methoxy allylic amine derivatives in good yields. The amino carbene complexes reacted with alpha,beta-unsaturated aldehydes to give substituted pyrroles in good yields.