Solvent- and Wavelength-Dependence of the Photocleavage of the Cyclobutane Ring in<i>N</i>,<i>N</i>′-Dibutyl-<i>c</i>-3,<i>c</i>-4-bis(2-hydroxyphenyl)-<i>r</i>-1,<i>c</i>-2-cyclobutanedicarboxamide
The ratio between two photocleavage directions of the cyclobutanering in the title compound varies with the solvent polarity and the irradiation wavelength, and the effect of the solvent polarity appears much larger in protic solvents than aprotic ones.
investigated. Though the lactone rings in coumarin dimers are very susceptible to nucleophilic ring-opening, heating these derivatives reformed six-membered lactone rings except for certain imide and diamide derivatives. The large neiboring group effect allowed the relactonization by the attack of hydroxyphenyl group to carbonyl carbon in preference to the scission of cyclobutanering.