Construction of Chiral Photochromic System Controlled by Steric Factors

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A sterically demanding and thermally irreversible bisthienylfulgides, 3,4-bis[1-(2,5-dimenthyl-3-thienyl) ethylidene]-3,4-dihydro-2,5-furandione, was synthesized by Pd-catalyzed carbonylation of the corresponding 2-butyne-1,4-diol derivatives and their photochromic bihaviers were studied.Treatment of trichloroethene with butyllithium followed by reaction of 3-acyl-2,5-dimenthylthiophene gave the acetylenediol in 45% yield. Reaction of acetylenediol with carbon monoxide in the presence of Pd(Oac)ィイD22ィエD2 afforded bisthienylfulgides as a mixture geometric isomers. These isomers were separated by silica gel column chromatography to obtain EE, EZ, and ZZ in 4, 3, and 1% yields, respectivity. The identification f geometric isomers was done by ィイD11ィエD1H NMR and their photochromic behaviors were studied. 366-nm light irradiation to the toluene solution of ZZ afforded EZ, EE, and two colored closed forms(CィイD2EEィエD2, CィイD2EZィエD2). Two colored closed forms changed EE and EZ upon 554-nm light irradiation. Two colored forms(CィイD2EEィエD2, CィイD2EZィエD2)obtained from EE and EZ were diastereomeic with each other. At photostationary state o 366-nm light irradiation, the ratio of concentration of the isomers, EE/EZ/ZZ/CィイD2EEィエD2/ CィイD2EZィエD2, was 17/14/8/58/3. The most notable feature is the highly diastereoselective formation of CィイD2EEィエD2 (90% de).