FLASH VACUUM THERMOLYSIS OF 5-(1-CHLOROETHENYL)ACENAPHTHENE - A SHORTSYNTHESIS OF PYRACYLENE AND ITS BEHAVIOR UNDER HIGH-TEMPERATURE CONDITIONS

Flash vacuum thermolysis (FVT) of 5-(1-chloroethenyl)acenaphthene (4) has been found to give rise to pyracylene (1). Pure 1 can be isolated from the 1100 degrees C pyrolysate by recrystallization at -20 degrees C. The temperature conversion data reveal that 1 decomposes and rearr anges at T greater than or equal to 1000 degrees C; acenaphthylene (11 ), 1-ethynyl- (23) and 3-ethynyl-acenaphthylene (24) have been identif ied. The formation of 23 and 24 indicates that 1 rearranges to the tra nsient cyclopent[bc]acenaphthylene (20) via a single ring-contraction- ring-expansion mechanism under FVT conditions. The experimental data a re supported by semiempirical AM1 calculations of the C14H8 potential energy surface.