Parabansäure‐Derivate Ein Beitrag zur Chemie der nucleophilen Carbene

Abstract

Die aus den Azoliumsalzen 3, 8 und 10 mit Triathylamin in situ erzeugten ,,nucleophilen Carbenoide" reagieren mit 2 Moll. Iso-und Isothio-cyanat iiber dipolare Zwischenprodukte (z. B. 12, 15) zu den Parabansaure-Derivaten 2, 4 und 9. Dabei ist das Auftreten eines freien Carbens wenig wahrscheinlich. Ein Mechanismus iiber ein elektronenreiches Olefin konnte ausgeschlossen werden. Parabanic Acid Derivatives. A Contribution to the Chemistry of Nucleophilic Carbenes"Nucleophilic carbenoids", produced in situ from the azolium salts 3, 8 and 10 with triethylamine, react with 2 moles of iso-and isothio-cyanate to yield the parabanic acid derivatives 2, 4 and 9 via dipolar intermediates (e. g. 12, 15). The appearance of free carbenes is improbable. A mechanism via an electron-rich olefin could be excluded.

1,3-Heterocumulene-to-Alkyne [3 + 2] Cycloaddition Reactions: A Theoretical and Experimental Study

“…Whereas there is no precedence for the first step of this reaction sequence in the literature, the addition of isothiocyanates to 1,3-thiazol-2-ylidenes to yield compounds analogous to 3 via a dipolar intermediate has been observed before. , Phenyl isothiocyanate gave an analogous addition product 3b , but as predicted by the calculations, the reaction proceeds slower and the yield was significantly lower (17%). The lower yield may be due to a reduced reactivity of phenyl isothiocyanate in relation to methyl isothiocyanate toward the carbene.…”

Triazaspirocycles: Occurrence, Synthesis, and Applications

“…Elimination of carbamates, analogous to the urea elimination observed by Ulrich et al has been described as well in the synthesis of NHCs [53]. Dimerization of imidazole-based carbenes results in the synthesis of bi-imidazoylidenes [54], which, upon addition of isocyanates, have been shown to produce a 1,4 dipole intermediate similar to that observed with the addition of isocyanates to NHCs (Scheme 6 ) [55-58]. Bi-imidazoylidenes have also been shown to oxidize in air to form peroxides (Scheme 7 ).…”

A Spirocyclic Parabanic Acid Masked N‐Heterocyclic Carbene as Thermally Latent Pre‐Catalyst for Polyamide 6 Synthesis and Epoxide Curing

“…[ 27 ] Finally, the reaction of peraminoethylenes with heterocumulenes deserves to be mentioned. [ 28–31 ]…”

“…[27] Finally, the reaction of peraminoethylenes with heterocumulenes deserves to be mentioned. [28][29][30][31] Free carbenes (1 equivalent) and phenyl isothiocyanate (1 equivalent) were shown to form a zwitterionic covalent compound. [32,33] Inter alia, the reverse fragmentation into a carbene and an isothiocyanate has been investigated.…”