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π-Expanded alkynes and alkenes are promising as organic materials like semiconductors, light-emitters, and dyes for photoelectric conversion. So far a number of π-expanded compounds were synthesized, and their optical and physical properties were investigated for future reference. We describe herein synthetic protocols of functionalized diarylethynes and ethenes by using benzyl sulfones and aldehydes as starting compounds. Both diarylethynes and ethenes were synthesized through diarylethenyl sulfones which were prepared by the consecutive base-assisted aldol-type reaction of benzyl sulfones with arylaldehydes, phosphorylation (acetylation), and base-assisted elimination of phosphoric (acetic) acid. When the ethenyl sulfones were treated with sterically hindered base like lithium hexamethyldisilazide (LiHMDS), sulfinic acid eliminated to give the desired ethynes. This synthetic protocol could be applied to the syntheses of highly strained cyclic diynes (Sondheimer-Wong diynes). The strained cyclic diynes were successfully transformed to diaminopentalenes through amination and transannulation by treatment with an excess amount of lithium amide/amine. On the other hand, when the ethenyl sulfones were subjected to perylene/blue LEDs-promoted reductive desulfonylation, the desired diarylethenes (stilbenes) were successfully synthesized. We also developed 1,3,6,8-tetra(4-alkoxyphenylethynyl)pyrene as visible-light driven photocatalyst. The pyrene photocatalyst accelerated the desulfonylation of ethenyl sulfones by irradiation of green light with LEDs, and afterwards the catalyst was successfully separated from the desired ethynes by column chromatography on silica gel.
Research papers (academic journals)
