Naphthoannelated Cycloheptatrienylidene and Cycloheptatetraene: Generation and Properties

Article abstract of DOI:10.1021/jo00147a028

A naphthoannelated cycloheptatrienylidene-cycloheptatetraene intermediate has been generated from both the corresponding tropone tosylhydrazone and a mixture of bromocycloheptatrienes.Thermolysis of the tosylhydrazone salt in cyclohexene or benzene gave only a mixture of naphthoannelated heptafulvalenes.Thermolysis of the tosylhydrazone salt in dimethyl fumarate gave the same two dimers-along with the expected spirocyclopropane adduct.Thermolysis of the tosylhydrazone salt or dehydrobromination of the mixture of bromocycloheptatrienes (21 and 22) with potassium tert-butoxide in the presence of diphenylisobenzofuran gave, in addition to the heptafulvalene dimers, an adduct that is believed to have arisen from rearrangement of an initially formed allene adduct.On the basis of the chemistry reported here as well as INDO calculations on a number of cycloheptatrienylidene-cycloheptatetraene pairs (and the triplets of the carbenes) it is suggested that initially formed singlet carbenes either intersystem cross to their triplet forms and show triplet chemistry (carbenes 12, 32, and 34) or drop to allene ground states to show at least some allene chemistry.The principal unanswered question is whether any bimolecular chemistry originates from any of the singlet carbenes.Calculations of Waali argue for all chemistry coming from the allene while some of the experimental observations are consistent with a carbene.