Asymmetric Cyclization Reaction of Diarylethene Derivatives:Specific Behavior in Bulk Amorphous Phase

概要

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Diarylethene derivatives having one or two chiral l-menthyl substituents were synthesized for the examination of an asymmetric photocyclization reaction. The compounds have been prepared from the corresponding carboxylic derivatives and l-menthol in the presence of dicyclohexylcarbodiimide. Upon irradiation with UV light these open form diarylethenes were converted into the corresponding closed-ring forms. Two diastereomers of the closed-ring form were separated by HPLC equipped with a silica-gel column, and their absorption spectra and CD spectra were measured. The two diastereomers gave the same absorption maximum and coefficient. The absolute stereochemistry of one of the diastereomers was determined by the CD spectrum. These compounds were found to undergo diastereoselective photocyclization reactions in the amorphous state. The product distribution between the diastereomers was almost 1 : 1 in a solution, but it deviated from 1 : 1 in the amorphous state. The predominantly formed diastereomer was (R, R) isomer : in case of the compound having twoBl-menthyl group, a diastereomer excess as large as 37.4% d. e. was obserbed in the amorphous state.
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