Cycloallene, 7 Ein Siebenringallen‐Dimer: Darstellung aus einem 7,7‐Dibromnorcaran‐Derivat und Thermolyse

Cycloallenes, 7. – A Seven‐Membered‐Ring Allene Dimer: Preparation from a 7,7‐Dibromonorcarane Derivative and Thermolysis Prepared by addition of dibromocarbene to 1,2‐dihydro‐3‐phenylnaphthalene, the 7,7‐dibromonorcarane derivative 6 gave the tetra‐ and pentacyclic hydrocarbons 7 and 8, respectively, on treatment with n‐butyllithium. The formation of 8 is considered to proceed via the 1,2‐cycloheptadiene derivative 15, which undergoes a dimerisation with the tetramethyleneethane diradical 16 as intermediate. Diradical 16 is also believed to be the intermediate in the thermal rearrangements of 8 to the penta‐ and hexacyclic hydrocarbons 12 and 13 and of 12 to 13. The structures of 8 and 13 have been determined by X‐ray structure analyses. Of special interest is the unusual length (165 pm) of the C‐12a – C‐12b bond (C‐1 – C‐22 in Figure 1) in 8.