Аннотация:The 2-(XC6H4)-substituted phenylcarbenes in which X = CH2, NH, O and S have been generated and pyrolysed in the gas phase at low pressure. When X = CH2 or NH, the main reaction is simple insertion into the adjacent o-position of the XC6H5 ring to give dihydroanthracenes and dihydroacridines respectively. The use of substituents shows that no spiro diene rearrangement is involved in the case X = NH. For X = O or S, on the other hand, the carbene inserts into the π-system ofthe XC6H5 ring and expansion occurs to give benzo[b]cyclohepta[d]furans and thiophens.
