ORGN 509 |
| 3,7-Dichloro-2,4,6,8-tetracarbomethoxybarbaralane I and 3,7-Dichloro-2,4,6,8-tetracarbomethoxy-semibullvalene 2 have been synthesized through the oxidative cyclization of the respective dihydro-dilithio-derivatives. The X-ray structure of 2 at 100 K showed a cyclopropane bond (C2/C8 = 1.60 Å) and an open-end distance (C4/C6 = 2.37 Å). VT NMR studies indicate a significant increase of the free energy of activation for the Cope rearrangement in 2 relative to the chlorine-free compound reported by us earlier. On the other hand, the X-ray structure of barbaralane 1 at RT and at 100K showed a symmetric structure with (C2/C8 and C4/C6 = 2.00 ± 0.002 Å). VT solution 13C-NMR measurements display no signal for C2/C4/C6/C8 between 5oC and -55oC. The experimental results will be correlated with DFT calculation on the substituent effects of 3,7 substitution.
|
|
Physical Organic Chemistry, Metal-Mediated Reactions, Asymmetric Reactions and Syntheses
8:00 PM-10:00 PM, Tuesday, August 21, 2007 BCEC -- Exhibit Hall - B2, Poster
Division of Organic Chemistry |
