Studies in the cycloproparene series: oxygen-containing 1H-cyclopropa[b]naphthalenes and their methylidene derivatives

3,6-Dimethoxy-1H- cyclopropa[b]naphthalene 4 is available from 1,4-benzoquinone in four steps in 27–28% overall yield. The diether 4 provides a range of methylidene derivatives 15a–e by way of the disilyl compound 14, and is efficiently demethylated by cerium(IV) ammonium nitrate to provide 1H-cyclopropa[b]naphthalene-3,6-dione 16 (85%) whose crystal structure is reported. Quinone 16 is the first stable cyclopropaquinone but it resists conversion into a 1-C exocyclic olefin. The chemistry of the compounds is described, their spectral data are discussed, and the cyclic voltammetry of 16 is provided.