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Neumann, Ralf; Herz, Hans‐Georg; Maas, G.

doi:10.1002/(sici)1521-3897(199902)341:2<121::aid-prac121>3.3.co;2-4

Cited by 3 publications

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“…The synthesis of semicyclic propyne iminium salts 1af, in which the iminium function is incorporated in a five-, six-, or seven-membered ring, has been reported. 10 When solutions of these salts in acetonitrile were heated in a thick-walled Schlenk tube, the results summarized in Scheme 1 were obtained. In the case of N-allyl-3,4,5,6tetrahydropyridinium salts 1c,d,e and of N-allyl-4,5,6,7tetrahydro-3H-azepinium salts 1g,h, a thermal isomerization reaction started to occur at about 120 °C.…”

Section: Resultsmentioning

confidence: 99%

Intramolecular [4 + 2] Cycloaddition Reaction of Six- and Seven-Membered Cyclic N-Allyl-C-arylethynyl Iminium Salts

2001

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N-Allyl-2-(het)arylethynyl-3,4,5,6-tetrahydropyridinium triflates 1c,d,e and N-allyl-2-(het)aryl-4,5,6,7-tetrahydro-3H-azepinium triflates 1g,h undergo a thermal isomerization reaction leading to derivatives of [a,f]-annulated isoindolium salts 2 in good yields. Similarly, N-allyl-2-phenylethynyl-pyridinium triflate 4 is transformed into the condensed pyridinium salt 5. An intramolecular [4 + 2] cycloaddition reaction, in which the (het)arylethynyl moiety acts as the 4pi component, is considered as the key step of this transformation. In contrast, the related N-allyl-4,5-dihydro-3H-pyrrolium salts 1a,b and N-homoallyl-3,4,5,6-tetrahydropyridinium salt 1f undergo unspecific decomposition under thermal impact.

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Section: Resultsmentioning

confidence: 99%

Intramolecular [4 + 2] Cycloaddition Reaction of Six- and Seven-Membered Cyclic N-Allyl-C-arylethynyl Iminium Salts

2001

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“…The methods for the preparation of alkyne iminium salts 1, which can formally be derived from aldehydes or ketones -or more exactly from vinylogous amides -have mainly been developed by Maas et al [2][3][4][5][6][7][8]. Alkinyl-alkoxymethyleniminium salts 2 have been prepared by the alkylation of propiolamides with triethyloxonium tetrafluoroborate [9][10][11][12][13][14] or methyl fluorosulfonate [15].…”

Section: Introductionmentioning

confidence: 99%

Orthoamides and iminium salts, LXXXIX. Reactions of N,N,N′,N′,N″,N″,N′″,N′″-octamethyl-acetylene-bis(carboxamidinium) tetrafluoroborate with nucleophilic reagents – new methods for the preparation of amidinium salts and ketene aminalsa

Drandarov

Tiritiris

Kantlehner³

2015

Zeitschrift Für Naturforschung B

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The acetylene-bis(carboxamidinium) salt 4 dehydrates carboxylic acids to the corresponding anhydrides, as the byproduct 2-oxo-but-2-en-amidinium salt 6b was isolated. Aromatic hydroxy compounds and 2-furyl-methylmercaptan add to the triple bond of the salt 4 to give 2-aryloxy-and 2-alkylmercapto-but-2-enebis(amidinium) salts 7-9. According to this reaction principle, 2-organoamino-buten-2-ene-bis(amidinium) salts 10 and 11 were prepared from 4 and primary and secondary amines, whereas 4-chlorobenzhydrazide reacted with 4 to give the imidazole-3-carboxamidinium salt 13. The reaction of CH 2 -acidic compounds as malononitrile or ethyl cyanoacetate with the bis(amidinium) salt 4 affords 2-cyanomethylene-but-3-enamidinium salts 15. With the CH-acidic diethyl 2-bromomalonate, compound 4 undergoes a Michael-initiated ring closure cyclopropenation reaction with further ring opening by the released Br -to the corresponding 2-diethoxycarbonylmethylene-3-bromo-but-3-enamidinium salt 18. Unlike cyclopentadiene and furane, the reaction of N-methylpyrrole and bis(amidinium) salt 4 does not lead to Diels-Alder [4 + 2] cycloadduct but to the Michaeltype 1:1 adduct 20. Pyrrole-and thiophene-2-carboxamidinium salts 23-25 can be prepared from compound 4 and esters of glycine, N-methylglycine (sarcosine), and mercaptoacetic acid, respectively. The derivatives of quinoxaline-2-carboxamidinium salts 29 are accessible from aromatic 1,2-diamines and compound 4. The reaction of the CH 2 /NH-acidic cyanoacetamide with the bis(amidinium) salt 4 produced the 3-pyrroline-2-on derivatives 33.

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“…R 1 -R 2 = (CH 2 ) n (n = 3-5) and R 3 = Me, homoallyl or benzyl. 1,6,7 In order to extend the applications of conjugated iminium salts 2 and 3, we wanted to introduce additional functionalization into propene iminium salts 2. To this end, we turned our attention to alkoxycarbonyl-substituted enaminoketones 4.…”

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“…3,4 They are also readily transformed into a wide range of propyne iminium triflates 3 by b-elimination of triflic acid (HOTf) (Scheme 1). [4][5][6] The NR 2 R 3 moiety in 2 and 3 can be a dialkylamino, morpholino, pyrrolidino or piperidino group (with R 1 = Me, Ph). Also, the iminium function can be incorporated in a ring system, e.g.…”

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Alkoxycarbonyl-Substituted 3-Trifloxypropene Iminium Salts and Iminium-Substituted Δ^2,3-Butenolides: Synthesis and Reactivity toward Nucleophiles

Nikolai¹,

Maas²

2003

Synthesis

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Triflic anhydride reacts regioselectively with the ethoxycarbonyl-substituted enaminones 6a-h to give the novel 3-trifloxypropene iminium salts 7a-d or iminium-substituted D 2,3 -butenolides 8a-d and 9a-d in good yields. Hydride reduction of the iminium salts 7a,b affords new 2-dialkylamino-4-trifloxy-but-3-enoates 13a,b, while mild hydrolysis generates 2-oxo-4-trifloxybutenoates 14a,b. Butenolides 8b,d, and 9c react with methyl hydrazine to afford 4-dialkylamino-pyridazin-3(2H)-ones 12a-c.Triflic anhydride (Tf 2 O) reacts readily with enaminones 1 to yield 3-trifloxypropene iminium triflates 2 which are useful substrates in nucleophilic vinylic substitution reactions 1,2 as well as intra-and intermolecular S E (Ar) reactions. 3,4 They are also readily transformed into a wide range of propyne iminium triflates 3 by b-elimination of triflic acid (HOTf) (Scheme 1). 4-6 The NR 2 R 3 moiety in 2 and 3 can be a dialkylamino, morpholino, pyrrolidino or piperidino group (with R 1 = Me, Ph). Also, the iminium function can be incorporated in a ring system, e.g. R 1 -R 2 = (CH 2 ) n (n = 3-5) and R 3 = Me, homoallyl or benzyl. 1,6,7 In order to extend the applications of conjugated iminium salts 2 and 3, we wanted to introduce additional functionalization into propene iminium salts 2. To this end, we turned our attention to alkoxycarbonyl-substituted enaminoketones 4. We wondered whether the geminal capto-dative substitution of the enone moiety in 4 would have an effect on the reactivity and regioselectivity of sulfonylation with triflic anhydride and whether the presence of an ester group in the ambident propene iminium moiety of salts 2 (R 1 = COOR) would affect the regioselectivity of a nucleophilic attack.Here, we describe the O-sulfonylation of 2-amino-4-oxobutenoates 4 with Tf 2 O and some reactions of the resulting products with nucleophiles.The required enaminoketones 6 were prepared by analogy to a published procedure 8 that was slightly modified (see Experimental Part): addition of the alkynyl lithium reagent derived from ethyl propiolate to an aromatic aldehyde followed by oxidation of the thus formed alcohol with MnO 2 (Scheme 2) yielded the acetylenic ketones 5.Conjugate addition of secondary amines to alkynylketones 5a, 9 b,c yielded regio-and stereoselectively ethyl 2-amino-4-oxo-butenoates 6a-h. 10 The 1 H NMR spectra (400 MHz) of compounds 6a,c,g showed remarkably broadened signals for the pyrrolidine ring, indicating a partial double bond character for the N-C2 and C3-C4 bond due to p-delocalization in the enaminoketone. A NOESY experiment for 6f suggested the E(2,3),Z(3,4) stereochemistry (Scheme 2).When Tf 2 O was added to cooled solutions of the 2-amino-4-oxobutenoic acid esters 6a-d in CH 2 Cl 2 , the yellow solutions turned reddish and the moisture-sensitive salts 7a-d were formed in good yield. They could be precipitated completely from the reaction solution by the addition of Et 2 O or pentane (Scheme 3). The constitution of the novel alkoxycarbonyl-substituted 3-trifloxypropene iminium salts 7 wa...

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Intramolecular [4 + 2] Cycloaddition Reaction of Six- and Seven-Membered Cyclic N-Allyl-C-arylethynyl Iminium Salts

Intramolecular [4 + 2] Cycloaddition Reaction of Six- and Seven-Membered Cyclic N-Allyl-C-arylethynyl Iminium Salts

Orthoamides and iminium salts, LXXXIX. Reactions of N,N,N′,N′,N″,N″,N′″,N′″-octamethyl-acetylene-bis(carboxamidinium) tetrafluoroborate with nucleophilic reagents – new methods for the preparation of amidinium salts and ketene aminalsa

Alkoxycarbonyl-Substituted 3-Trifloxypropene Iminium Salts and Iminium-Substituted Δ^2,3-Butenolides: Synthesis and Reactivity toward Nucleophiles

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Cited by 3 publications

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Intramolecular [4 + 2] Cycloaddition Reaction of Six- and Seven-Membered Cyclic N-Allyl-C-arylethynyl Iminium Salts

Intramolecular [4 + 2] Cycloaddition Reaction of Six- and Seven-Membered Cyclic N-Allyl-C-arylethynyl Iminium Salts

Orthoamides and iminium salts, LXXXIX. Reactions of N,N,N′,N′,N″,N″,N′″,N′″-octamethyl-acetylene-bis(carboxamidinium) tetrafluoroborate with nucleophilic reagents – new methods for the preparation of amidinium salts and ketene aminalsa

Alkoxycarbonyl-Substituted 3-Trifloxypropene Iminium Salts and Iminium-Substituted Δ2,3-Butenolides: Synthesis and Reactivity toward Nucleophiles

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Alkoxycarbonyl-Substituted 3-Trifloxypropene Iminium Salts and Iminium-Substituted Δ^2,3-Butenolides: Synthesis and Reactivity toward Nucleophiles