Isolation of Novel Radical Cations from Hydroquinone Ethers. Conformational Transition of the Methoxy Group upon Electron Transfer
摘要:
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.
PROCESS FOR THE COVALENT COUPLING OF TWO MOLECULES BY MEANS OF A DIELS-ALDER REACTION WITH INVERSE ELECTRON REQUIREMENT
申请人:Wiessler Manfred
公开号:US20100016545A1
公开(公告)日:2010-01-21
The present invention relates to a process for linking two molecules by means of a Diels Alder reaction with inverse electron requirement (DARinv), comprising the following steps: reaction of a (a) triazine or tetrazine with one or more electron-attracting substituents on the ring as a diene component, the electron-attracting substituents being selected from:
COOR
C(O)NR
2
CX
3
(X=halogen)
halogen
CN
SO
2
—R or SO
3
—R
PR
2
wherein R═H, alkyl, aryl, heterocycle, which in turn may be substituted, where appropriate, with alkyl, OH, SH, halogen, aryl, heterocycle, nitro, carboxyamido or amine group. —heterocyclic rings having 1, 2 or 3 N, O or S atoms with a ring size of 5 or 6 ring members, which are substituted with at least one carboxyl, sulfonic acid or phosphone group with (b) an isolated double bond or triple bond in a (hetero)carbocyclic ring or an isolated olefinic double bond or triple bond in a linear or branched hydrocarbon chain which may also contain heteroatoms, where appropriate, as a dienophile component.