| Summary: | 博士 === 東海大學 === 化學系 === 103 === In part one, an efficient base-mediated three-component reaction of 4-hydroxycoumarin, acetone, and amine (or enamine) for the synthesis of various substituted pyranocoumarins was described. This methodology was further applied to the design and synthesis of a potential thermochromic colorant.
In part two, 3-benzoyl-4-benzylamino-7-dimethylaminocoumarin was synthesized and its conformation in solid state and solution was determined. While the X-ray crystal analysis showed an aromatic - stacking interaction in solid state, the proton NMR studies suggested the presence of an intramolecular hydrogen bonding in solution. Adjacent functional group modifications through N-methylation, reduction of carbonyl group, or replacing the coumarin moiety to dimedone, all resulted in disrupting the - aromatic stacking conformation. Upon UV irradiation, the 7-methylamino group can be oxidized by molecular oxygen to the corresponding formamide in the absence of any external photosensitizers. Further, two coumarin/pyrrole-fused heterocycles were synthesized to explore their photochemical and redox-switching properties. Photooxidation of the prepared colorless pyrrolocoumarin resulted in a distinct change to red and a sharp decrease in fluorescence intensity. The photooxidized product can be swiftly reverted to the original form by either NaCNBH3 reduction or hydrogenation.
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