title: Synthesis, molecular structure, and chiroptical properties of dibenzylidene derivatives of bicyclo[3.3.1]nonane and brexane.
abstract: 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.
authors.affiliation: Department of Organic Chemistry, Vilnius University, Vilnius, Lithuania.
authors.forename: Sigitas
authors.initials: S
authors.lastname: Stončius
authors.affiliation: Department of Organic Chemistry, Vilnius University, Vilnius, Lithuania.
authors.forename: Algirdas
authors.initials: A
authors.lastname: Neniškis
authors.affiliation: Centre for Analysis and Synthesis, Department of Chemistry, Lund University, Lund, Sweden.
authors.forename: Nagarajan
authors.initials: N
authors.lastname: Loganathan
authors.affiliation: Centre for Analysis and Synthesis, Department of Chemistry, Lund University, Lund, Sweden.
authors.forename: Ola F
authors.initials: OF
authors.lastname: Wendt
mesh_terms: D000473:Alkanes / Q000737:chemistry*; D001597:Benzylidene Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D060326:Chemistry Techniques, Synthetic; D008958:Models, Molecular; D008968:Molecular Conformation; D011789:Quantum Theory; D013237:Stereoisomerism
chemical_list: D000473:Alkanes; D001597:Benzylidene Compounds; C017573:nonane
keywords: CD spectroscopy; TDDFT calculations; enones; exciton coupling; styrene chromophore