Syntheses of dithienylcyclopentene optical molecular switches

Article abstract of DOI:10.1002/1099-0690(200301)2003:1<155::AID-EJOC155>3.0.CO;2-S

Properly functionalized dithienylethenes show promise for light-induced switching processes. To prevent cis/trans isomerization from competing with conrotatory 6π-electron ring closure, the ethene segment is usually incorporated in a (perfluorinated) cyclopentene. In the present article syntheses of perhydrocyclopentene 1 and perfluorocyclopentene 2 are described, which are amenable for large-scale conversions. Both compounds have chloro substituents at the 5-position of the thiophene rings to allow further functionalization. The conversion of the chloro substituents of 1 to formyl, carboxylate, boronyl, and hydrogen groups by halogen/lithium exchange at room temperature is described, and examples are given of further elaboration of 1 and 2 by attachment, both in a symmetrical as well as unsymmetrical fashion, of additional functionality by condensation, Friedel-Crafts or Suzuki reactions. The newly prepared thienylperhydrocyclopentene derivatives show reversible photochromism if the substituents at the 5-postions allow for conjugation with the thiophene π-system. Wiley-VCH Verlag GmbH & Co KGaA, 69451 Weinheim, Germany, 2003.