Propiniminium‐Salze – Synthese, [2 + 2]‐ und [2 + 4]‐Cycloadditionen

Abstract

Alkine, die einen resonanzstabilisierten kationischen Substituenten tragen, sind bislang wenig bekannt. Vertreter dieser Substanzklasse enthalten fast durchweg einen Propiniminium-Strukturteil. So kennt man die eigentlichen Propiniminium-Salze 1 a I ) sowie Propiolamidinium-(1 b2)) und Propiolamidium-Salze (1 c3-')). Der kationische Substituent in l a -d kann auch Bestandteil eines Heterocyclus sein 1-Chlorpropiniminium-Salze (1 a, R2 = CI) scheinen nicht sehr stabil zu sein'.". Anders als ihre olefinischen Verwandten (z. B. 3-Chlor-und 3-Alkoxypropeniminium-Salze *), Vinamidinium-Salze 9)) sind Propiniminium-Systeme praparativ kaum genutzt worden; ihre Reaktivitat ist dementsprechend wenig mit Beispielen belegt. Dabei kann man davon ausgehen, daD die Iminium-Funktion die C = C-Bindung starker polarisiert und aktiviert, als es fur die analogen Carbonylsubstituierten Alkine der Fall ist4).In dieser Arbeit berichten wir daher exemplarisch uber die Reaktivitat von Propiniminium-Salzen des Typs 1 a, die wir auf einem bisher nicht genutzten Weg erstmals hergestellt haben.

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

“…Compared with the bisamidinium salt 4, the four-carbon atoms chain in 6b is not linear anymore, and the C-C-C angles with 119. 2 The bis(amidinium) salts 7a-c are formed by the conjugated addition of phenol or naphthols to the acetylenebis(carboxamidinium) salt 4 in nearly quantitative yield at room temperature (r.t.) (Scheme 3). Obviously, this type of reaction is also possible with polyhydric phenols, as could be de monstrated by the formation of the six-fold charged salt 8 from compound 4 and phloroglucinol.…”

“…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].…”

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

“…Attempts to induce HOTf elimination from 7a in order to synthesize alkoxycarbonyl-substituted propyne iminium salts, using (dimethylaminomethyl)polystyrene as a base, 5 were unsuccessful: only an oily residue was isolated, its 1 H NMR spectra indicating unselective decomposition of the substrate under the reaction conditions (r.t., CH 2 Cl 2 , 1 h). An IR spectrum of the product mixture did not reveal the presence of a C≡C bond.…”

“…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.…”

[2+2] Cycloadditions of electron-poor acetylenes to endocyclic enaminones: ring-expansion reactions

“…14,15 On this basis, a simple metal-free synthesis of 2-alkyl-, 2-cycloalkyl-, 2-aryl-and 2-heteroaryl-substituted pyridine-3,4-dicarboxylates and their N-oxides have been reported. 16 The electron-poor propyne iminium triflates, prepared from 3-trifloxypropene iminium triflates by elimination of triflic acid, underwent [2þ2] and [2þ4] cycloadditions 17 with enamines. Their reactivity towards imines has also been reported.…”