Neue Wege zu Pentalen‐Vorstufen

New Pathways to Precursors of Pentalene Pentalene dimers 2 and 3 are easily available in moderate yields by CuCl 2 ‐induced oxidative coupling of dilithium‐pentalenediide ( 5 ) ( Scheme 1 ). On the other hand, NBS bromination of 1,5‐dihydropentalene ( 4 ) or of 1,2‐dihydropentalene ( 8 ) gives unstable 1‐bromo‐1,2‐dihydropentalene ( 9 ), while subsequent in ‐ situ elimination with Et 3 N exclusively gives syn ‐ cis ‐pentalene dimer 2 in moderate yields ( Scheme 3 ). NMR‐Spectroscopic evidence for compounds 2 , 3 , and 9 is presented, and mechanistic alternatives for the formation of pentalene dimers 2 and 3 are discussed.