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Synthesis and photochemical investigations of tetrasubstituted alkenes as molecular switches--the effect of substituents.

Molecular switches based on helical tetrasubstituted alkenes, substituted with either electron-withdrawing (CF(3), F, CN; 2a-c, 3a,c) or -donating substituents (Me, OMe; 2d,e), have been synthesized from acyclic precursors 4 and 5 in a domino carbopalladation/Stille reaction. This palladium-catalyzed process allowed the rapid assembly of two C-C bonds, two six-membered rings, and the tetrasubstituted double bond in a completely diastereoselective fashion. The electronic effects of the substituents on the overall switching process were investigated by alternating irradiation of two different wavelength regions. Although the substituents had only a small influence on the absorption maxima, drastic differences in the switching behavior were observed.