3.On the other hand, the rearrangement of the tricycle 1 could take place via retro-Diels-Alder reaction or via diradicals as intermediates. The conversion into 3 might be initiated by rupture of the C2-C3 and/or C1-C6 bonds.Hydrogenation (Pt/C, pentane) of 1 affords 4-and 5methyl-2,3-benzobicyclo[3.1 .O]hex-2-ene in 55 and 25% yield, respectively, whereby the C1 -C2 and C2-C3 bonds of one three-membered ring of the spiropentane moiety are broken. German version: Angew. Chem. 95 (1983) 892 The complete version of this communication appears in: Angew. Chem. Suppl. [5] a) Thermolyses in sealed NMR tubes in a thermostat (+O.0SoC), recording of the ' H -N M R spectra at ca. 0°C; b) standard deviations according to the least squares method. [6] 5-Methylene-l,3-~yclohexadiene, a structural subunit in 3, undergoes the ene reaction with TCNE at RT: D. Hasselmann, K. Loosen, Angew. Chem. 90 (1978) 641; Angew. Chem. lnt. Ed. Engl. 17 (1978) 606.