Petrosamine (1) is an alkaloid isolated from the marine sponge Petrosia sp. collected at Belize. The colors of petrosamine solutions vary significantly with solvent; The bis adduct 4 of anthracene diendoxide 1 and tetraphenylcyclone is a synthetic equivalent for linear benzodifuran 2; it reacts thermally with dienophiles including some exceedingly weak ones to give linear acene derivatives (Table I).