31349-66-3Relevant academic research and scientific papers
Facile synthesis of 5-To 7-membered benzolactam compounds via strongly facilitated electrophilic aromtic substitution reaction
Kurouchi, Hiroaki,Otani, Yuko,Ohwada, Tomohiko
, p. 705 - 713 (2017/04/10)
We employed our system to activate aromatic ring-Tethered carbamate compounds with trifluoromethanesulfonic acid to obtain benzolactams with 5-To 7-membered rings, and examined the substrate scope and limitations of this activation method. In 5-membered ring formation, a halogen group on the aromatic ring did not greatly affect the reaction yield, but other electron-donating groups inhibited the cyclization reaction, and various side-reactions occurred. In 7-membered ring formation, eletron-donating groups on aromatic ring promoted the cyclization reaction, but cyclization of electron-deficient aromatic rings did not proceed well. The 6-membered ring formation reaction showed the greatest substrate generality.
Protonation switching to the least-basic heteroatom of carbamate through cationic hydrogen bonding promotes the formation of isocyanate cations
Kurouchi, Hiroaki,Sumita, Akinari,Otani, Yuko,Ohwada, Tomohiko
, p. 8682 - 8690 (2014/07/21)
We found that phenethylcarbamates that bear ortho-salicylate as an ether group (carbamoyl salicylates) dramatically accelerate O-C bond dissociation in strong acid to facilitate generation of isocyanate cation (N-protonated isocyanates), which undergo subsequent intramolecular aromatic electrophilic cyclization to give dihydroisoquinolones. To generate isocyanate cations from carbamates in acidic media as electrophiles for aromatic substitution, protonation at the ether oxygen, the least basic heteroatom, is essential to promote C-O bond cleavage. However, the carbonyl oxygen of carbamates, the most basic site, is protonated exclusively in strong acids. We found that the protonation site can be shifted to an alternative basic atom by linking methyl salicylate to the ether oxygen of carbamate. The methyl ester oxygen ortho to the phenolic (ether) oxygen of salicylate is as basic as the carbamate carbonyl oxygen, and we found that monoprotonation at the methyl ester oxygen in strong acid resulted in the formation of an intramolecular cationic hydrogen bond (>C=O+-H...O) with the phenolic ether oxygen. This facilitates O-C bond dissociation of phenethylcarbamates, thereby promoting isocyanate cation formation. In contrast, superacid-mediated diprotonation at the methyl ester oxygen of the salicylate and the carbonyl oxygen of the carbamate afforded a rather stable dication, which did not readily undergo C-O bond dissociation. This is an unprecedented and unknown case in which the monocation has greater reactivity than the dication.
