Darstellung und Photochemie eines (Anthrylvinyl)thiophenfulgids

The base-catalyzed reaction of isopropylidenesuccinate 2 with phenylthienylpropenone 1a does not give a Stobbe condensation to 3a but results in an 1,4-addition to 7 which under the basic conditions reacts further to 8 by an intramolecular condensation. The (anthrylvinyl)thiophene fulgide 4c is obtained, however, from 3-glyoxyloyl-2,5-dimethylthiophene hydrate (11) via the 2H-pyran 14: Wittig olefination of 14 with the phosphonium salt 16 leads to the diester 3c which easily is converted to Z,E-4c. - Irradiation of Z,E-4c gives a mixture of all four possible E,Z isomers of 4c and the ring-closed valence tautomers Z- and E-17. All isomers could be separated and characterized. Compound 18, formed irreversibly in a thermally-induced reaction, is enriched during irradiation.