Synthesis and characterization of novel BINOL-based symmetrical and asymmetrical axially chiral dendrimers

• Main Author: Gobouri, Adil Abdullah H.
• Other Authors: Gardiner, John
• Published: University of Manchester 2012
• Subjects: 668.9; BINOL Dendrimers - Axially Chiral Dendrimers
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.553383

Synthesis of optically active dendrimers based on 1,1'-bi-2-naphthol enantiomers and their derivatives as core units is growing rapidly due to the unique behavior and properties of the new compounds and their various valuable applications in several fields such as asymmetric catalysts, enantioselective fluorescent sensors and in chiral molecular recognition. To the best of our knowledge, the synthesis of binaphthyl-based symmetrical and asymmetrical axially chiral dendrimers via 1,3-cycloaddition reactions ["Click" chemistry] using Fréchet-type dendrons and their azido-analogues has not been studied yet. The principal aim of this project was the synthesis and characterization of a novel series of binaphthyl-based symmetrical and asymmetrical axially chiral dendrimers via "Click" and etherification reactions, and then determination of the specific and molar rotation of the new dendrimers to investigate the influence of linkage nature between the dendritic wedges and the core units on the optical properties in presence of the triazole ring by comparing of the properties of the new dendrimers with the dendrimers reported in literature, in addition to study the influences of different chemical groups near the dendritic wedges on the optical properties of the novel synthesized dendrimers. In conclusion, several families of novel BINOL-based symmetrical and asymmetrical axially chiral dendrimers have been synthesized by the reaction of well-known BINOL derivatives as core units with Fréchet-type dendrons and their azido-analogues via "Click" and etherfication reactions for the first time. All new dendrimers were obtained in very good yields which confirm the effectiveness of "Click" reaction in this type of synthesis. The new dendrimers were fully characterized by 1H, 13C and HMQC NMR spectroscopy, mass spectrometry, IR spectroscopy and UV-Vis spectrometry. All new dendrimers show moderate optical activity. Changes in the specific and molar rotation are characterized by a general decrease in the specific rotation and a general increase in the molar rotation with the increase in the dendritic wedges generation in each series of the synthesized dendrimers. By our current knowledge, the increase in the specific rotation as generation increases of (S)-358, (S)-359 and (S)-360 observed in this research is the first such observation. The presence of the triazole ring in the linkage between the core unit and the dendritic wedges plays an important role in reducing of the steric repulsion between the two naphthyl units and in reducing of the effect of the dendritic wedges generation on the torsional angle by making the wedges far away from the attachment point of the two naphthyl units.