Activation of Electrophilicity of Stable Y-Delocalized Carbamate Cations in Intramolecular Aromatic Substitution Reaction: Evidence for Formation of Diprotonated Carbamates Leading to Generation of Isocyanates
Kurouchi, H; Kawamoto, K; Sugimoto, H; Nakamura, S; Otani, Y; Ohwada, T
| HERO ID | 1449168 |
|---|---|
| In Press | No |
| Year | 2012 |
| Title | Activation of Electrophilicity of Stable Y-Delocalized Carbamate Cations in Intramolecular Aromatic Substitution Reaction: Evidence for Formation of Diprotonated Carbamates Leading to Generation of Isocyanates |
| Authors | Kurouchi, H; Kawamoto, K; Sugimoto, H; Nakamura, S; Otani, Y; Ohwada, T |
| Journal | Journal of Organic Chemistry |
| Volume | 77 |
| Issue | 20 |
| Page Numbers | 9313-9328 |
| Abstract | Although cations with three heteroatoms, such as monoprotonated guanidine and urea, are stabilized by Y-shaped conjugation and such Y-conjugated cations are sufficiently basic to be further protonated (or protosolvated) to dications in strongly acid media, only O-monoprotonated species have been detected in the case of carbamates even in magic acid. We found that the trifluoromethanesulfonic acid catalyzed cyclization of arylethylcarbamates proceeds to afford dihydroisoquinolones in high yield. In strong acids, methyl carbamates are fully O-monoprotonated, and these monocations do not undergo cyclization even under heating. But, as the acidity of the reaction medium is further increased, the cyclization reaction of methyl phenethylcarbamates starts to proceed as a first-order reaction, with a linear relationship between rate and acidity. The sign and magnitude of the entropy of activation Delta S-double dagger were found to be similar to those of other A(Ac)1 reactions. These results strongly support the idea that further protonation of the O-protonated carbamates is involved in the cyclization, but the Concentration of the dications is very low and suggests that the rate determining step is dissociation of methanol from the diprotonated Carbamate to generate protonated isocyanate, which reacts with the aromatic ring. Therefore, O-protonated carbamates are weak bases in sharp contrast to other Y-shaped monocations. |
| Doi | 10.1021/jo3020566 |
| Pmid | 23025848 |
| Wosid | WOS:000309951700050 |
| Is Certified Translation | No |
| Dupe Override | No |
| Comments | Source: Web of Science WOS:000309951700050Scopus URL: https://www.scopus.com/inward/record.uri?eid=2-s2.0-84867730257&doi=10.1021%2fjo3020566&partnerID=40&md5=dcd85b512033cc24c49b60caad600993 |
| Is Public | Yes |
| Language Text | English |
| Keyword | Acid media; Aromatic rings; Aromatic substitution reactions; Cyclization reactions; Dications; Electrophilicity; Entropy of activation; First order reactions; Heteroatoms; High yield; Linear relationships; Methyl carbamate; Monocations; Protonated; Rate determining step; Reaction medium; Sharp contrast; Strong acids; Weak basis; Aromatic compounds; Methanol; Positive ions; Protonation; Substitution reactions; Urea; Cyclization; 2 2 chlorophenylethylcarbamic acid methyl ester; 2 2 fluorophenethylcarbamic acid methyl ester; 2 3 chlorophenethylcarbamic acid methyl ester; 2 3 fluorophenethylcarbamic acid methyl ester; 2 3 nitrophenylethylcarbamic acid methyl ester; 2 3 tolylethylcarbamic acid methyl ester; 2 4 chlorophenethylcarbamic acid methyl ester; 2 4 fluorophenethylcarbamic acid methyl ester; 2 4 methoxyphenylethylcarbamic acid methyl ester; 2 4 nitrophenylethylcarbamic acid methyl ester; 2 4 tolylethylcarbamic acid methyl ester; 2,4 dichlorophenethylcarbamic acid methyl ester; 3,4 dihydro 2h isoquinolin 1 one; 5 chloro 3,4 dihydro 2h isoquinolin 1 one; 5 fluoro 3,4 dihydro 2h isoquinolin 1 one; 6 chloro 3,4 dihydro 2h isoquinolin 1 one; 6 fluoro 3,4 dihydro 2h isoquinolin 1 one; 6 methyl 3,4 dihydro 2h isoquinolin 1 on; 7 chloro 3,4 dihydro 2h isoquinolin 1 one; 7 fluoro 3,4 dihydro 2h isoquinolin 1 one; 7 hydroxy 3,4 dihydro 2h isoquinolin 1 one; 7 methyl 3,4 dihydro 2h isoquinolin 1 one; 8 chloro 3,4 dihydro 2h isoquinolin 1 one; 8 fluoro 3,4 dihydro 2h isoquinolin 1 one; 8 methyl 3,4 dihydro 2h isoquinolin 1 one; [2 (2 fluoro 5 methyl phenyl)ethyl]carbamic acid methyl ester; carbamic acid derivative; isocyanic acid derivative; phenetylcarbamic acid methyl ester; trifluoromethanesulfonic acid; unclassified drug; article; catalysis; chemical bond; chemical reaction; chemical structure; cyclization; electrophilicity; entropy; proton nuclear magnetic resonance; proton transport; substitution reaction; Carbamates; Cations; Isocyanates; Molecular Structure; Protons |