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'-H-2(2)] and [1-C-13] isotopomers have been prepared and py rolysed. Argon matrix infrared spectroscopy showed nu(2) bands at 2207.7, 2 207.0, and 2168.5 cm(-1) respectively for the three pentatetraenone isotopo mers. 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 b ut also yielded 9,10-dihydro-9,10[1',2']-benzenoanthracene.