Flow-vacuum pyrolysis of three dibenzocycloalkanones

The flow-vacuum pyrolyses of 10H-dibenzo[a,d]cyclohepten-10-one (9), 5H-11, 12-dihydrodibenzo[a,d]cycloocten-10-one (10) and 11,12-dihydro-6H-dibenzo[a ,e]cycloocten-5-one (11) were studied by GC/MS at 1.33 mbar and temperature s between 600 and 900 degreesC. The ketone 9 affords anthracene and small a mounts of anthrone. The product distributions of ketones 10 and 11 are very similar: besides anthracene (major product) and 9-methyl-anthracene (minor product) the 5H-10,11-dihydro-dibenzo[a,d]cycloheptene (2) was formed as a n isolable intermediate. Trahanovsky's pyrolysis mechanism (including spira nes and bridged diradicals) suggested for dibenzosuberones and dibenzocyclo octanes can be extended to ketones 9-11 las well as to hydrocarbon 2). Cons ideration of enantiomeric spiranes as intermediates can conduct to a better understanding of the reaction mechanism. (C) 2001 Elsevier Science B.V. Al l rights reserved.