Stončius Sigitas, Neniškis Algirdas, Loganathan Nagarajan, Wendt Ola F
Department of Organic Chemistry, Vilnius University, Vilnius, Lithuania.
Centre for Analysis and Synthesis, Department of Chemistry, Lund University, Lund, Sweden.
Chirality. 2015 Oct;27(10):728-37. doi: 10.1002/chir.22480. Epub 2015 Jul 17.
Synthesis of several enantiomerically pure unsaturated bicyclo[3.3.1]nonane and related brexane (tricyclo[4.3.0.0(3,7) ]nonane) derivatives bearing exocyclic benzylidene substituents from readily available (+)-(1S,5S)-bicyclo[3.3.1]nonane-2,6-dione was accomplished. Molecular geometry and chiroptical properties of compounds with enone and styrene chromophores were studied by X-ray diffraction analysis, molecular modeling, and circular dichroism (CD) spectroscopy. Difunctional 3,7-dibenzylidenebicyclo[3.3.1]nonanes, such as and , exhibited intense CD couplets, arising from the exciton coupling between the two unsaturated chromophores. The observed negative sign of the exciton couplets is congruent with the negative twist (negative chirality) defined by the two interacting transition dipoles. The sign of the Cotton effect corresponding to the π→π* transitions in the CD spectra of monoenone and tricyclic brexane acetate was correlated with the intrinsic dissymmetry (helicity) of the styrene chromophore.
以易于获得的(+)-(1S,5S)-双环[3.3.1]壬烷-2,6-二酮为原料，合成了几种对映体纯的不饱和双环[3.3.1]壬烷及相关的布雷烷（三环[4.3.0.0(3,7)]壬烷）衍生物，这些衍生物带有环外亚苄基取代基。通过X射线衍射分析、分子建模和圆二色性（CD）光谱研究了具有烯酮和苯乙烯发色团的化合物的分子几何结构和手性光学性质。双官能团的3,7-二亚苄基双环[3.3.1]壬烷，如和，表现出强烈的CD偶合，这是由两个不饱和发色团之间的激子耦合引起的。观察到的激子偶合的负号与两个相互作用的跃迁偶极所定义的负扭转（负手性）一致。单烯酮和三环布雷烷乙酸酯的CD光谱中对应于π→π*跃迁的科顿效应的符号与苯乙烯发色团的固有不对称性（螺旋性）相关。
