화학공학소재연구정보센터
Journal of the American Chemical Society, Vol.125, No.19, 5741-5744, 2003
Stereochemical memory versus Curtin-Hammett behavior in the rearrangement of 1,3-cyclopentanediyl radical cations derived from housanes through structural effects on conformational control
The electron-transfer-catalyzed rearrangement of the housanes 1 affords regioselectively the two cyclopentenes 2 and 3 by 1,2-migration of a group at the methano bridge. Appropriate ring annelation in the intermediary cyclopentane-1,3-diyl radical cation 1(.+) changes the stereochemical course of the rearrangement from complete stereoselectivity (stereochemical memory) for the structurally simple housane 1b to partial loss of stereoselectivity through competing conformational interconversion for the tricyclic housane 1c. Additional cyclohexane annelation, as in the tetracyclic housane 1a, results in complete loss of stereocontrol through Curtin-Hammett behavior, as substantiated by the viscosity dependence on the product ratio of the rearrangement. Whereas in the radical cations 1b(.+) and 1c(.+) the 1,2-shifts (k(2) and k(3)) are faster than the conformational anti reversible arrow syn change (k(1), k(-1)), the reverse applies for the radical cation 1a(.+). Such structural manipulation of conformational effects in radical cation rearrangements has hitherto not been documented.