Nonbenzenoid aromatic compounds containing a fused four-membered ring. Formation and properties of benzo[3,4]cyclobuta[1,2]cyclohepten-6-one derivatives
Abstract
The ring-enlargement reaction of 1-methoxybiphenylene with dichlorocarbene gives 5-chlorobenzo[3,4]cyclobuta[1,2]cyclohepten-6-one (6) as well as fluorenone derivatives (7) and (8), although in low yields. Similar reactions of 2-methoxybiphenylene and its derivatives give the corresponding benzocyclobutacycloheptenones (11), (12), (14), (15), (17), and (18). The spectral data of the benzocyclobutacycloheptenones suggest that the four-membered ring assumes a tetramethylenecyclobutane (or dimethylenecyclobutene) form, excluding a potential cyclobutadiene form, and the seven-membered ring resembles the tropone ring of benzocycloheptenone.