111635-03-1Relevant articles and documents
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, Hiroaki,Kawamoto, Kyoko,Sugimoto, Hiromichi,Nakamura, Satoshi,Otani, Yuko,Ohwada, Tomohiko
, p. 9313 - 9328,16 (2012/12/11)
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 ΔS ? were found to be similar to those of other AAc1 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.
Radical transfer hydroamination with aminated cyclohexadienes using polarity reversal catalysis: Scope and limitations
Guin, Joyram,Mueck-Lichtenfeld, Christian,Grimme, Stefan,Studer, Armido
, p. 4498 - 4503 (2008/02/03)
The synthesis of various new 1-aminated-2,5-cyclohexadienes is described. These reagents can be used in radical transfer hydroaminations of unactivated and electron-rich double bonds. With thiols as polarity reversal catalysts good yields are obtained. The radical hydroamination occurs with good to excellent anti-Markovnikov selectivity. Many functional groups such as alcohols, silyl ethers, phosphonates, arylbromides, imides, amides, and also acidic protons are tolerated under the reaction conditions. DFT calculations provide insights into the aromatization of silyl, alkyl, and aminyl substituted cyclohexadienyl radicals to generate the corresponding C-, Si-, and N-centered radicals.
TIN TETRACHLORIDE-INDUCED ?-CYCLIZATIONS OF GLYCINE CATION EQUIVALENTS TO SUBSTITUTED PIPECOLIC ACID DERIVATIVES
Esch, Peter M.,Boska, Ilona M.,Hiemstra, Henk,Boer, Richard F. de,Speckamp, W. Nico
, p. 4039 - 4062 (2007/10/02)
Cationic ?-cyclization reactions of N-(3-alkenyl)-N-(methoxycarbonyl)acetoxyglycine esters induced by tin tetrachloride in dichloromethane are described.Reactions started and quenched with water at -78 deg C mainly yield cis-4-hydroxypipecolic esters, whereas reactions quenched after warm-up to room temperature provide trans-4-chloropipecolic esters as major products.A mechanistic scheme is advanced which adequately explains these results.The essentials are a rapid cationic aza-Cope equilibrium of the incipient iminium cation, and participation of the ester moiety through formation of a relatively stable bicyclic dioxycarbenium cation as pivotal intermediate.
Conformational and steric aspects of the inhibition of phenylethanolamine N-methyltransferase by benzylamines
Grunewald,Sall,Monn
, p. 433 - 444 (2007/10/02)
Compounds of the benzylamine (BA) class are potent inhibitors of phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1.28). Restriction of the aminomethyl side chain through its incorporation into a cyclic framework as in 1,2,3,4-tetrahydroisoquinoline (
