Formation of biphenylene by elimination of C2 from 9,10-didehydrophenanthrene at 1100°C

Abstract Flash vacuum pyrolysis of phenanthrene-9,10-dicarboxylic anhydride 5 and of 2,2-dimethyl-5-(9′-fluorenylidene)-1,3-dioxan-4,6-dione 8 at 1100°C/0.03–0.04 mm Hg gave pyrolysates which were analysed by 1 H NMR spectroscopy and shown to contain phenanthrene 9 as a major constituent and biphenylene 2 as a minor one.