Synthesis and properties of photochromic furofurans

476-484The deep blue-violet bis-o-quinonemethide 3 cyclizes thermally in a [4s+4a]cycloaddition reaction, yielding the colourless [3,2- b]furofurane 1a. The latter is re-opened by irradiation with UV light back to the methide in its Z,Z- configuration 2a. By metallation of 1a, the highly photoreactive acetylene 8a is obtained which again forms a methide under irradiation, but now in its E,E-configuration 3. The properties of this unique new photochromic system and related furofurans and alkyneshave been investigated