Synthesis of Precursors for the Pyrolytic Formation of Pentatetraenones

3-(9',10'-Dihydro-9',10'-ethanoanthracen-11'-ylidene)prop-2-enoyl chloride and its [12',12'- 2 H2] and [1- 13 C] isotopomers have been prepared and pyrolysed. Argon matrix infrared spectroscopy showed ?2 bands at 2207 . 7, 2207 . 0, and 2168 . 5 cm-1 respectively for the three pentatetraenone isotopomers. The pyrolysate of the 12'-methyl substituted precursor showed a band at 2205 cm-1 which was tentatively assigned to methylpentatetraenone. The 12'-ethenyl substituted precursor gave a pyrolysate showing ketene bands but also yielded 9,10-dihydro-9,10[1',2']-benzenoanthracene.