1582767-13-2Relevant academic research and scientific papers
The Advantages of Cyclic Over Acyclic Carbenes To Access Isolable Capto-Dative C-Centered Radicals
Mahoney, Janell K.,Jazzar, Rodolphe,Royal, Guy,Martin, David,Bertrand, Guy
, p. 6206 - 6212 (2017)
A cyclic and an acyclic di(amino)carbene as well as a cyclic and an acyclic (alkyl)(amino)carbene cleanly react with benzoyl chloride to give the corresponding adducts 1+cyc, 1+acy, 2+cyc, and 2+acy, respectively. The reduction of 1+cyc and 2+cyc derived from cyclic carbenes affords the corresponding radicals 1cyc and 2cyc that are stable at room temperature. In contrast, radicals 1acy and 2acy, derived from acyclic carbenes, cannot be isolated. It is shown that 1acy is as thermodynamically stabilized as its cyclic counterpart 1cyc, but its instability is the result of β-hydrogens of the nitrogen substituent, along with the enhanced flexibility around C?N bonds, which allow for a H.-migration-elimination process. Radical 2acy is thermodynamically unstable, and undergoes disproportionation into the corresponding iminium 2+acy and enolate 2?acy. This is due to the excessive steric hindrance, which prevents electron-delocalization on the NCCO fragment, and thus, the capto-dative stabilization. This work suggests general guidelines for the design of highly persistent (amino)(carboxy)radicals, especially by emphasizing the key advantage of cyclic patterns.
Comparative reactivity of different types of stable cyclic and acyclic mono- and diamino carbenes with simple organic substrates
Martin, David,Canac, Yves,Lavallo, Vincent,Bertrand, Guy
, p. 5023 - 5030 (2014/04/17)
A series of stable carbenes, featuring a broad range of electronic properties, were reacted with simple organic substrates. The N,N-dimesityl imidazolylidene (NHC) does not react with isocyanides, whereas anti-Bredt di(amino)carbene (pyr-NHC), cyclic (alkyl)(amino)carbene (CAAC), acyclic di(amino)carbene (ADAC), and acyclic (alkyl)(amino)carbene (AAAC) give rise to the corresponding ketenimines. NHCs are known to promote the benzoin condensation, and we found that the CAAC, pyr-NHC, and ADAC react with benzaldehyde to give the ketone tautomer of the Breslow intermediate, whereas the AAAC first gives the corresponding epoxide and ultimately the Breslow intermediate, which can be isolated. Addition of excess benzaldehyde to the latter does not lead to benzoin but to a stable 1,3-dioxolane. Depending on the electronic properties of carbenes, different products are also obtained with methyl acrylate as a substrate. The critical role of the carbene electrophilicity on the outcome of reactions is discussed.
