REARRANGEMENT OF CYCLOHEPTATRIENYLIDENES IN SOLUTION

Factors that could promote the rearrangement of cycloheptatrienylidene to phenylcarbene in solution were studied. Simple dilution and increase of the temperature to 240 °C were not sufficient for the rearrangement of the parent cycloheptatrienylidene to be competitive with dimerization to heptafulvalene. Rearrangement did appear when dimerization was retarded by 2, 7-disubstitution. 2, 7-Diphenylcycloheptatrienylidene was thermally and photolyti-cally generated from the corresponding tosylhydrazone salt and gave exclusively 9-phenylfluorene, the product expected from carbene-carbene rearrangement. 2, 7-Dimethyltropone was synthesized next, but could not be converted to its tosylhydrazone. 2, 7-Dimethylcycloheptatrienylidene was therefore generated by dehydrochlorination of 2-chloro-1, 3-dimethylcycloheptatriene. At 100 °C, tetramethylheptafulvalene was exclusively formed, but at 150160 °C, in addition to 37% of dimer, 31% of o-methylstyrene (from the rearrangement) was isolated. Finally, attempts were made to generate 2, 7-diethylcycloheptatrienylidene by dehydrochlorination of 2-chloro-1, 3-diethylcycloheptatriene. Conditions could not be found in which base-induced elimination was competitive with thermal aromatization. © 1978, American Chemical Society. All rights reserved.