Regiochemistry in 1,3-Dipolar Cycloadditions of the Azomethine Ylide Formed from Diethyl Aminomalonate and Paraformaldehyde (original) (raw)
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1,3-Dipolar Cycloadditions of Phenanthridinium-Based Azomethine Ylides
Bulletin des Sociétés Chimiques Belges, 1994
Azomethine ylides generated from 5-(alkoxycarbonylmethyl)phenanthridinium cations were studied in 1,3dipolar cycloadditions with dimethyl maleate and dimethyl fumarate as dipolarophiles. The cycloadducts with the pyrrolidino[l,2-f]phenanthridine skeleton easily underwent dehydrogenation. The structure of products was determined by X-ray, NMR and MS.
Collection of Czechoslovak Chemical Communications, 1999
Reaction of a series of N-alkyl-and N,N-dialkylbromoacetamides 1a-1e with phenanthridine afforded quaternary phenanthridinium salts 2a-2e. These compounds treated with triethylamine form azomethine ylides which undergo a cycloaddition reaction with activated C=C bond, giving 3-(N-alkylcarbamoyl)-1,2,3,12b-tetrahydropyrrolo[1,2-f]phenanthridines 3a-3e, 4c, 5c, 6c or 3-(N-alkylcarbamoyl)-2,3-dihydropyrrolo[1,2-f]phenanthridine 7c. Their stereochemistry was studied by NMR spectroscopy. The best results were obtained with fumaronitrile as a dipolarophile. It has been found that the ylides react in syn conformations but if 1-adamantyl moiety is bound to the ylide, it reacts in anti conformation, too. The azomethine ylides show a very poor reactivity towards dimethyl fumarate or dimethyl maleate. Yet we could prepare products for ylide bearing 1-adamantyl group.
[3+2] Dipolar cycloadditions of an unstabilised azomethine ylide under continuous flow conditions
Tetrahedron Letters, 2010
The [3+2] dipolar cycloaddition reactions of the unstabilised azomethine ylide precursor benzyl(methoxymethyl)(trimethylsilylmethyl)amine with 12 electron-deficient alkenes in the presence of catalytic trifluoroacetic acid are examined under continuous flow conditions (20-100°C, 10-60 min residence time). The more reactive and hazardous alkenes such as ethyl acrylate, N-methylmaleimide and (E)-2-nitrostyrene afford substituted N-benzylpyrrolidine products in 77-83% yields, whereas less reactive dipolarophiles such as (E)-crotononitrile and ethyl methacrylate give lower yields (59-63%). Under optimised conditions, the reaction with ethyl acrylate is scaled up to afford ethyl N-benzylpyrrolidine-3-carboxylate (30 g, 87%) in 1 h.
Mediterranean Journal of Chemistry, 2013
Phtaloylimidophenylalanyl-2-hydroxymethylaziridine has been used as a starting material to yield azomethine ylide through thermal opening and was then involved into 1,3-dipolar cycloaddition reactions. Different five-membered adducts were obtained and were fully identified. The latter might be considered useful starting materials for further functionalization to provide novel compounds of biological interest.
The synthesis of amino acids by 1,3-dipolar cycloadditions of azomethine ylides
Tetrahedron, 1985
Thiaxolium ylides react with a variety of dipolarophiles to afford adducts. After filtration chromatography, a tricyclic adduct is obtained. The tricyclic adducts react with potassium t-butoxide/tbutanol to provide dihydropyrroles. The adducts also react with tributyltin hydride to form compounds in which the thiaxolidine ring has been cleaved. These adducts can be hydrolyzed under acidic conditions to form pyrrolidines. The desulfurization procedure is signiticant in that none of the relative asymmetry derived from the dipolar cycloaddition is lost. The synthesis of a-allokainic acid has been achieved from adduct 16s.
Tetrahedron, 1990
Arylidene imines of a-amino esters undergo cycloaddition to ethyl phenylpropiolate, methyl propiolate and dimethyl acetylenedicarboxylate (ADE) on heating in toluene (110%) or o-xylene (135-145oC). The reactions proceed via stereospecific azomethine ylide formation and give single 3-pyrroline cydoadducts in moderate to good yield. Reaction of certain of the imines with 2 mol. of ADE leads to a pyrroles formed by rearrangement. The mechanism of the rearrangement is discussed. The facile generation of novel "NH" azomethine ylides by 1,2-prototropy in imines of a-amino acids and esters (1) (Scheme 1) is well established.3 Azomethine ylide formation occurs stereospecifically giving (2) under kinetic control. 4 The extensive use of aziridines as precursors of azomethine ylides, via a thermal conrotatory ring opening, stemming from the early pioneering work of Heine, Huisgen and Padwa5 led us to suggest that aziridines would be expected to participate in the Scheme 1 equilibria.6 We have never detected such intermediates but a recent report disclosed that the reaction of certain arylidene imines of a-amino esters with acyl chlorides leads to the formation of isolable Nacylaziridines. ' A wide range of other electron-withdrawing substituents can replace the carboxylic acid/ester moiety in (1) and give rise to analogous dipoles.' Typically the uncatalysed thermal 1,2prototropy occurs on heating the imines at ca. 80-140°C in a suitable solvent. However, we showed some time ago that azomethine ylide formation from (1) is markedly accelerated by both weak Lewis and Bronsted acid catalysts.' More recently we reported that a wide range of metal salts [Ag(l), Li(l), Zn(ll), Mg(ll), Co(ll), Mn(ll), Ti(lV)] in combination with triethylamine and a polar solvent enable these azomethine ylides to be rapidly generated and trapped at room temperature. 'O*" The Ti(lV) catalysed processes show an interesting and synthetically useful reversal of the normal cycloaddition regiochemistry (Scheme 2)' 2 We have previously reported details of the cycloaddition of (1) to maleate and fumarate esters, and to cyclic dipolarophiles.4v6 We now report related studies with acetylenic dipolamphiles. These studies were completed before we developed the metal ion catalysed methodology." Ethyl Phenylproplolate as Dipolarophlle The reaction of imines, or the imine moiety of heterocycles such as pyrfdine or thiazole, with acetylenes, and in particular dimethyl acetylenedicarboxylate (ADE), is well documented.