Ciclofanos quirais de 1,3-dietinilalenosíntese, caracterización e estudo das súas propiedades quiropticas

Resumo

A new (2,6)pyrido[14_2]allenoacetylenyc cyclophane MC[14_2] was prepared by two routes: The first route involved the synthesis of MC[14_2] from the diethynyallene (±)-DEA-TIPS. This allenophane was obtained as a mixture of two pairs of enantiomers (P,P,P,P)/(M,M,M,M)-MC[14_2] and (P,P,M,P)/(M,M,P,M)-MC[14_2] and three achiral isomers (P,M,M,P)-MC[14_2], (P,M,P,M)-MC[14_2] and (P,P,M,M)-MC[14_2] in a 1:4:1:1:1 predicted statistical distribution. This mixture was resolved by HPLC and the relative configuration of the different stereoisomers could be assigned thanks to their symmetry and chirality by NMR, HPLC in a chiral stationary phase, dichroism circular spectroscopy X-Ray analysis and theoretical calculations. The second route involved the resolution of the starting material, the diethynylallene DEA-OH, by HPLC in a chiral stationary phase. Subsequent reactions and the conservation of the enantiomeric purity provided the macrocycle (P,P,P,P)-MC[14_2] and its enantiomer enantiomerically pure. (P,P,P,P)-MC[14_2] can present three possible conformations: cis, trans and twist. In solid phase, this macrocycle presents a geometry close to the theoretical twist conformation. To discern which conformation is present in solution or if the allenophane is better described as an average of them, it was carried out an experimental and theoretical study (CAM-B3LYP 6-31G(d) level of theory) of its chiroptical propertiers (ECD, VCD and ORD). The comparison of experimental and theoretical ECD and ORD spectra strongly suggests the twist conformation as the predominant in solution. The study of the solvent effect in this system show that chloroform solvent molecules can establish weak hydrogen bonds with the pyridine ring of the macrocycle. The chiral macrocycle presents bistability. The two possible states reversibility exchanged by addition of TFA or Et3N and present very different quiroptical responses, therefore opening access to novel chiral molecular switches. Finally, incorporation of new aromatic spacers into the macrocycle, such as idolizinyl moieties, offers the possibility of new systems with fascinating properties. The indolizinyl aromatic spacer was synthesised from 2-enynylpyridines. To shed light about this process computational and experimental reactivity studies were performed. These studies support that a nucleophile assisted E-Z isomerization followed by a pseudocoarctate cyclization that leads to a nucleophilic singlet carbene is responsible for the transformation of (E)-enynylpyridines into the corresponding indolizines.