| Summary: | The dehydrobenzannulene (E,E)-1,3-(3,4:9,10-dibenzododeca-1,11-diene-5,7-diyne-1,12-diyl)benzene, C26H16, was successfully synthesized via photocatalyst-assisted stereoselective reductive desulfonylation of 1,3-bis{1-phenylsulfonyl-2-[2-(trimethylsilylethynyl)phenyl]ethenyl}benzene, C44H42O4S2Si2, and subsequent desilylative cyclization of the resulting (E,E)-bis-silyl-protected dienyne, C32H34Si2. The structure of the dehydrobenzannulene thus obtained was confirmed by single-crystal X-ray analysis; three benzene rings are connected to one another by a 1,3-butadiynylene and a pair of ethenylene arrays. Although the π-system expanded efficiently in the dehydrobenzannulene, it was observed that the butadiynylene and ethenylene arrays were strained, showing smaller [171.3 (2)–172.6 (2) °] and larger bond angles [122.5 (2)–131.9 (2)°] than the conventional bond angles, respectively. In CHCl3, the dehydrobenzannulene showed the longest absorption band at 377 nm. When irradiated by UV light, it emitted fluorescence at 468 nm (ΦF = 0.26) and 504 nm (ΦF = 0.24) in CHCl3 and in the powdered state, respectively.
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