Bis[1,2,3,4,5,6,7,8-octahydro-1,4:5,8-di(ethano)anthryl]carbene. The first all-hydrocarbon triplet diphenylcarbene having a half-life over one second under normal conditions
Bis[1,2,3,4,5,6,7,8-octahydro-1,4:5,8-di(ethano)anthryl]carbene. The first all-hydrocarbon triplet diphenylcarbene having a half-life over one second under normal conditions
Isolation of Novel Radical Cations from Hydroquinone Ethers. Conformational Transition of the Methoxy Group upon Electron Transfer
作者:Rajendra Rathore、Jay K. Kochi
DOI:10.1021/jo00119a017
日期:1995.7
Hydroquinone ethers as the bis-annulated derivatives R1-R3 are excellent electron donors by virtue of the facile oxidation to their radical cations R1(.+), R2(.-), and R3(.-) that are readily isolable as unusually robust SbCl6- and BF4- salts persistent in air for prolonged periods. Although the gas-phase vertical ionization potentials of the methyl ethers R1a and R2a are the same (IP = 7.83 +/- 0.01 eV), the oxidation potential of R1a in dichloromethane solution is less positive than that of R2a (E(1/2) = 1.11 and 1.30 V, respectively). The significantly lower value of E(1/2) for R1a relative to R2a, despite minimal changes in structure, is attributed to the conformational change that can occur in the radical cation. Indeed, X-ray crystallographic analysis of R1a, R2a, and R1a(.-) shows that the increased donor strength of R1a is derived from the enhanced (resonance) stabilization of R1a(.-), in which the methoxy group undergoes a 90 degrees rotation to the favorable coplanar conformation with respect to the aromatic ring. The subtle variation in the molecular structures of R1 and R2 accounts for the difference in nonbonded steric effects arising from the bridgehead alpha-hydrogens toward the methoxy groups.
Organocatalytic Asymmetric Hydrolysis of Epoxides
作者:Mattia Riccardo Monaco、Sébastien Prévost、Benjamin List
DOI:10.1002/anie.201400170
日期:2014.7.28
The hydrolytic ring opening of epoxides is an important biosynthetic transformation and is also applied industrially. We report the first organocatalytic variant of this reaction, exploiting our recently discovered activation of carboxylic acids with chiral phosphoric acids via heterodimerization. The methodology mimics the enzymatic mechanism, which involves an enzyme‐bound carboxylate nucleophile
Bis[1,2,3,4,5,6,7,8-octahydro-1,4:5,8-di(ethano)anthryl]carbene. The first all-hydrocarbon triplet diphenylcarbene having a half-life over one second under normal conditions
作者:Hideo Tomioka、Hidetaka Itakura、Katsuyuki Hirai
DOI:10.1039/a706663e
日期:——
Bicyclo[2.2.2]octyl groups are demonstrated to be very effective kinetic protectors for triplet carbenes.