An electron donor-acceptor complex and thermal triplex as intermediates in the cycloaddition reaction of N-vinylcarbazole with dimethyl 2,2-dicyanoethylene-1,1-dicarboxylate

Organic and polymer chemistry of electrophilic tri‐ and tetrasubstituted ethylenes

“…In the polymerization of dimethyl cyanofumarate with p ‐methoxystyrene, second‐order kinetics in the monomer were observed, in agreement with the proposed mechanism of initiation by a tetramethylene diradical 4. The kinetics in the case of N ‐vinylcarbazole with dimethyl 1,1‐dicyanoethylene‐2,2‐dicarboxylate are more complex because the cyclobutane adduct forms first and then reopens to the zwitterionic intermediate, which then reacts with additional N ‐vinylcarbazole and initiates the cationic homopolymerization of the latter20, 21 (Scheme ).…”

“…The fact that these electrophilic tri‐ and tetrasubstituted ethylenes with donor monomers in solution at room temperature reacted at reasonable rates made them very suitable for kinetics studies. We were able to provide clean examples of both tetramethylene biradical‐initiated copolymerization4 and tetramethylene zwitterion‐initiated cationic homopolymerization 20, 21. In the polymerization of dimethyl cyanofumarate with p ‐methoxystyrene, second‐order kinetics in the monomer were observed, in agreement with the proposed mechanism of initiation by a tetramethylene diradical 4.…”

“…As mentioned previously, heavily substituted cyclobutanes can revert back to zwitterions and thus initiate cationic polymerization. This scenario was clearly demonstrated in the reactions of N ‐vinylcarbazole with tetrasubstituted ethylenes, and the kinetics concurred 20, 21. 3‐Vinyl‐ N ‐ethylcarbazole and other monomers were also polymerized by a cationic mechanism in the presence of their cyclobutane adduct 46, 47…”

X‐Ray Characterization of an Electron Donor–Acceptor Complex that Drives the Photochemical Alkylation of Indoles

“…[1,2] Accordingly, the association of an electron-rich substrate with an electron-accepting molecule can bring about the formation of a new molecular aggregate, called an electron donor-acceptor (EDA) complex. [5] As a common trait of these synthetic studies, the existence of EDA complexes as relevant reactive intermediates has generally been inferred from spectroscopic changes of the absorption spectra. In many cases, the energy of this transition lies within the visible frequency range.…”

“…Over the last six decades, the photophysical properties of EDA complexes have been extensively studied, [3,4] while their use in synthetic chemistry has found limited applications. [5] As a common trait of these synthetic studies, the existence of EDA complexes as relevant reactive intermediates has generally been inferred from spectroscopic changes of the absorption spectra. In contrast, their isolation and structural characterization by X-ray single-crystal analysis, which provides more compelling mechanistic information, was possible in only a few cases.…”