On new N-heterocyclic carbene derived alkylidene imidazolines

Abstract

A series of novel 2-alkylidene imidazolines has been synthesized from imidazolium halides and substituted alkyl halides in the presence of base. The resultant exocyclic enediamines have been characterized and their nucleophilicity has been evaluated upon NMR spectroscopic data and substitution reactions.

N‐Heterocyclic Carbene Catalyzed Umpolung of Michael Acceptors for Intermolecular Reactions

“…This deoxy Breslow intermediate [16] 10 adds to another molecule of 1 to form the ester enolate 11, which undergoes proton transfer and elimination of the NHC to form the observed product 2. A strong indication for the presence of 10 comes from the fact that the stoichiometric reaction of NHC precursor 3, DBU, and butyl methacrylate 1 a in a 1:1:1 ratio resulted in the smooth formation of the corresponding protonated species 10·HClO 4 [Eq.…”

“…Our current study commenced with the NHCcatalyzed umpolung of the b position of n-butyl methacrylate (1 a) to give dibutyl 2,5-dimethylhex-2-enedioate (2 a; Table 1). After extensive investigation, we found that treatment of 1 a with the carbene generated by deprotonation of the 1,3,4-triphenyltriazolium salt 3 [10] with DBU resulted in the smooth formation of hex-2-enedioate 2 a in 71 % yield and an excellent E/Z ratio of 97:3 (based on 1 H NMR spectroscopy; Table 1 16), and the yield of the product was reduced considerably when the amount of DBU was halved (Table 1, entry 17). Delightfully, increasing the amount of DBU led to full conversion, which led to the formation of 2 a in 96 % yield and an excellent diastereoselectivity of 96:4 (Table 1, entry 18).…”

Umpolung mit N‐heterocyclischen Carbenen: Generierung und Reaktivität von Breslow‐Intermediaten (2,2‐Diaminoenole)

“…[9] Alternativ kann das Intermediat 2 irreversibel zum Keton 3 isomerisieren. Unsere Schlussfolgerung wurde zudem durch eine kinetische Studie von Mayr et al [11] gestützt, in der kürzlich die Reaktivität von 2-Benzyliden-Derivaten ("Desoxy-Breslow-Intermediate", d. h. ohne Enol-Hydroxyfunktion), [12] ab-geleitet von IMes (1 b) und SIMes (1 d) sowie vom 1,2,4-Triazolyliden 1 a, gegenüber Benzhydryliumionen als Elektrophil untersucht wurde. [10] Unsere Versuche, durch Behandlung der Ketone 3 mit verschiedenen Säuren, Basen sowie Silylierungsmitteln Tautomerisierung zu deren reaktiven Enolformen 4 zu erreichen, blieben erfolglos -sie führten zumeist zur Zersetzung oder zur Bildung von isomeren Silylenolethern.…”

Synthesis and properties of heteroaromatic carbenes of the imidazole and triazole series and their fused analogues

“…336 Although the reactivity of carbene 81A is inferior to that of its 4,5-dihydro analogue by about 2.5 times, the aromatic azolium methylide is three orders of magnitude more reactive than its 4,5-dihydro analogue.…”